On the afternoon of February 4, 1997, an eight month old child, Matthew Happen, was rushed to Children’s Hospital in Boston with a severe head injury. Despite emergency treatment, Matthew’s condition deteriorated, and he died on February 9, 1997. On March 5, 1997, a Middlesex County grand jury returned an indictment against the defendant, Louise Woodward, for the murder of Matthew. She subsequently was ordered held without bail. Woodward had worked as an au pair for the Happen family since November, 1996. Matthew was in Woodward’s sole care from the morning of February 4, on the departure of Matthew’s mother for work, until he was taken to the hospital.
Trial on the murder charge against Woodward commenced on October 6, 1997. After a three-week trial, the judge gave the jury instructions on murder in the first and second degrees. At Woodward’s request and over the Commonwealth’s objection, the judge did not instruct the jury on manslaughter.1 On October 30, 1997, the jury returned a guilty verdict of murder in the *661second degree. On the following day, the judge imposed the statutorily mandated term of life in prison.
On November 10, 1997, after hearing argument on Woodward’s motion for postjudgment relief, the judge reduced the jury’s verdict from murder to involuntary manslaughter, acting pursuant to Mass. R. Grim. R 25 (b) (2), 378 Mass. 896 (1979), and vacated the life sentence. He denied Woodward’s request for a required finding of not guilty or for a new trial. In a hearing that same afternoon after release of his memorandum and order reducing the verdict and vacating Woodward’s sentence, the judge imposed a sentence of 279 days for Woodward’s manslaughter conviction, that sentence being deemed served by Woodward while incarcerated awaiting trial and while awaiting action on her postconviction motion.
The Commonwealth and Woodward filed cross appeals. The Commonwealth then sought relief before a single justice, pursuant to G. L. c. 211, § 3.* 2 The single justice reserved and reported the case without decision to the full court, and ordered the parties’ respective cross appeals be consolidated with that reservation and report and entered in this court. The Commonwealth here seeks reinstatement of the jury’s verdict of murder in the second degree. In the alternative, the Commonwealth asks that we exercise our general superintendence power, G. L. c. 211, § 3, and resentence Woodward ourselves or remand the case to the Superior Court for reconsideration of Woodward’s rule 25 (b) (2) motion or for resentencing by another judge. Woodward appeals from the judge’s refusal to dismiss the indictment and his denial of her motion for a required finding of not guilty. She also raises a number of other claimed trial errors, but waives them if we should uphold the judge’s reduction of the verdict from murder to involuntary manslaughter, and the sentence he imposed.
*662I. The Commonwealth’s Appeal
The Commonwealth argues that the judge abused his discretion in reducing the jury’s verdict from murder to a manslaughter conviction. It points out that he should not have declined the Commonwealth’s request for a manslaughter instruction. It argues that these errors,3 in combination, impaired the integrity of the justice system and require that, pursuant to our extraordinary power of superintendence over the lower courts, we vacate the judge’s postverdict order and restore the jury’s verdict of murder in the second degree and the resulting mandated life sentence.
1. The jury instructions. The Commonwealth presented evidence that the cause of Matthew’s death was severe head trauma inflicted on February 4, 1997, while he was in the sole custody of Woodward.4 The Commonwealth sought jury instructions on murder in the first degree on a theory of extreme atrocity or cruelty,5 murder in the second degree, and on the lesser included offense of involuntary manslaughter. Woodward objected to the last request, and asked that the jury be limited to considering the offense of murder. The judge acceded to her request.6 This was error. We have stated repeatedly that, “[wjhen the evidence permits a finding of a lesser included offense, a *663judge must, upon request, instruct the jury on the possibility of conviction of the lesser crime.” Commonwealth v. Gould, 413 Mass. 707, 715 (1992). See Commonwealth v. Hobbs, 385 Mass. 863, 871 (1982); Commonwealth v. Richmond, 379 Mass. 557, 562 (1980); Commonwealth v. Campbell, 352 Mass. 387, 392 (1967). We have never limited this rule to requests made by the defendant, nor have we ever held that the Commonwealth is not entitled, evidence permitting, to such an instruction on request.* *****7
This issue has arisen on appeal most often in cases in which the defendant requested an instruction on a lesser included offense. In the only case of which we are aware concerning the Commonwealth’s request for a lesser included instruction, which presented the converse of the question here, we affirmed a judge’s allowance of the request over the defendant’s objection. Commonwealth v. Thayer, 418 Mass. 130, 132-133 (1994). See Commonwealth v. Matos, 36 Mass. App. Ct. 958, 962 (1994) (defendant does not have absolute right to make tactical decisions that determine which theories of criminal liability are submitted to jury); Commonwealth v. Vasquez, 27 Mass. App. Ct. 655, 660 (1989) (test to determine if instruction on lesser included offense required does not depend on whether defendant or Commonwealth objects, but rather whether evidence supports *664such instruction). Here, a disputed element — malice — distinguishes murder, the greater offense, from manslaughter, the lesser offense, and an instruction should have been given. Consideration of lower court denials of prosecutors’ requests for instructions on lesser included offenses would not reach us except in the unlikely procedural circumstances of this case, because the Commonwealth has no reason to appeal from a conviction, and is barred by double jeopardy principles from appealing from an acquittal. See Commonwealth v. Therrien, 383 Mass. 529, 532 (1981). Authorities elsewhere hold overwhelmingly that the prosecution has a right to jury instructions on lesser included offenses, on request, if the evidence so warrants, in spite of a defendant’s objection.8 As far as we are aware, no jurisdiction that has considered the issue has allowed a defendant to veto a lesser included offense instruction properly requested by the prosecution.
Our conclusion that the Commonwealth was entitled to a manslaughter instruction is fortified by the policy favoring instructing juries on lesser included offenses. The doctrine serves the public purpose of allowing the jury to convict of the offense established by the evidence, rather than forcing them to choose *665between convicting the defendant of an offense not fully established by the evidence or acquitting, even though the defendant is guilty of some offense. Commonwealth v. Walker, 426 Mass. 301, 305 (1997).9 Here, it was peculiarly inappropriate for the judge to refuse to charge the jury on manslaughter when, as revealed by his subsequent order reducing the jury’s verdict, in his view the evidence was not consonant with a conviction of murder. The jury, in reaching their verdict, surely must have concluded that the Commonwealth had proved beyond a reasonable doubt the element of causation — that Woodward’s acts caused Matthew’s fatal injury. By refusing to accede to the Commonwealth’s request for a manslaughter instruction, the judge impermissibly prevented the jury from considering a lesser degree of culpability for Woodward.
The judge’s error, however, did not prejudice the Commonwealth’s case against Woodward in the final analysis. The Commonwealth concedes that the jury’s verdict rendered the error harmless. See Commonwealth v. Matos, 36 Mass. App. Ct. 958, 962 (1994) (no prejudice where jury instructed, over defendant’s objection, on involuntary manslaughter and defendant convicted of murder in the second degree). If the judge had honored the Commonwealth’s request and the jury had received the manslaughter instruction but had declined to choose that option, the judge could still have reduced the jury’s murder verdict under rule 25 (b) (2). See, e.g., Commonwealth v. Gaulden, 383 Mass. 543, 552 (1981). Alternatively, had the *666jury been given such a choice and returned a manslaughter verdict, the trial’s outcome would have yielded the same conviction of Woodward as the judge’s postverdict order.
2. Rule 25 (b) (2) reduction in verdict. General Laws c. 278, § 11, provides in part that “the judge may on a renewed motion for a directed verdict of not guilty pursuant to the Massachusetts Rules of Criminal Procedure set aside the verdict and order a new trial, or order the entry of a finding of guilty of any offense included in the offense charged in the indictment or complaint.” Rule 25 (b) (2) incorporates this statutory authority.10 The authority of the trial judge under rule 25 (b) (2) to reduce the verdict or grant a new trial in criminal cases is much like our authority to review so-called capital cases — convictions of murder in the first degree — under G. L. c. 278, § 33E. See Commonwealth v. Carter, 423 Mass. 506, 513 (1996); Commonwealth v. Gaulden, 383 Mass. 543, 553 & n.7 (1981).
The postconviction powers granted by the Legislature to the courts at both trial and appellate levels reflect the evolution of legislative policy promoting judicial responsibility to ensure that the result in every criminal case is consonant with justice. See Gaulden, supra at 553-554 & n.7; Commonwealth v. Brown, 376 Mass. 156, 167-168 (1978); Commonwealth v. Baker, 346 Mass. 107, 109 (1963).11 It is clear that the responsibility may be exercised by the trial judge, even if the evidence warrants the jury’s verdict. “[A] new trial or verdict reduction may be proper even when the evidence can legally support the jury’s verdict.” Commonwealth v. Carter, supra at 512. See Commonwealth v. Ghee, 414 Mass. 313, 321 (1993) (reduction in verdict not based on absence of evidence warranting jury’s *667finding of deliberate premeditation but because more consonant with justice); Commonwealth v. Keough, 385 Mass. 314, 319-321 (1982) (jury’s verdict of guilty of murder warranted by evidence, but reduction to manslaughter upheld because more consonant with justice). The judge’s option to reduce a verdict offers a means to rectify a disproportionate verdict, among other reasons, short of granting a new trial. Gaulden, supra at 556. The judge’s power under rule 25 (b) (2), like our power under G. L. c. 278, § 33E, may be used to ameliorate injustice caused by the Commonwealth, defense counsel, the jury, the judge’s own error, or, as may have occurred in this case, the interaction of several causes. See, e.g., Commonwealth v. Millyan, 399 Mass. 171, 188-189 (1987) (judge’s failure to instruct on intoxication because defendant did not so request and such instruction was inconsistent with defense strategy was nonetheless, in light of evidence on intoxication, appropriate justification for judge to reduce verdict).
Because such broad postconviction authority is vested in the trial judge, we have counseled that a judge should use this power sparingly, Keough, supra at 321, and trial judges have in fact used their rule 25 (b) (2) power infrequently. Since 1979, the Commonwealth has appealed verdict reductions in only ten cases, of which seven were affirmed.12 We see no evidence of any generalized abuse of the power vested in trial judges since the rule’s adoption. Nor do we see any other reason to modify *668case law that we have developed since 1979 following legislative authorization of the rule.
In convictions of murder in the first degree, we are authorized to review a whole case, including the evidence. G. L. c. 278, § 33E. In a noncapital case such as this, we do not conduct an independent analysis when a trial judge reduces a verdict to a lesser offense. Gaulden, supra at 557.13 Our review of a trial judge’s exercise of his authority under rule 25 (b) (2) is more constrained: “In assessing a trial judge’s decision to reduce a verdict under [that rule], ‘we consider only whether the judge abused his discretion or committed an error of law.’ ” Commonwealth v. Millyan, supra at 188, quoting Gaulden, supra. “We defer to the trial judge because he has the advantage of face to face evaluation of the witnesses and the evidence at trial. He is in a far better position than we are to make the judgment required by the rule.” Commonwealth v. Cobb, 399 Mass. 191, 192 (1987), citing Gaulden, supra. We. have made it clear that under rule 25 (b) (2), a judge may review all the evidence, including the defendant’s version of the facts, in deciding whether the verdict comports with justice, even when the evidence warranted the jury’s verdict. See Ghee, supra at 321-322; Keough, supra at 319. Indeed, “the judge is not foreclosed *669from considering the defendant’s testimony . . . and, if he believes it, relying on it.” Keough, supra at 321. The Commonwealth’s complaint in this case, that the judge “substituted” his view of the evidence for that of the jury, is no reason to overrule his decision to reduce the verdict. See Ghee, supra at 321 (Commonwealth’s argument that judge erred in reducing verdict where there was evidence supporting verdict of murder in first degree characterized as “meritless” and “miss[ing] the point”).
We do expect a judge to state the reasons for a reduction in verdict. Gaulden, supra at 556. In this case, the judge has done so. After “[vjiewing the evidence broadly,” in accordance with his accurate understanding of rule 25 (b) (2) powers, the judge gave as his first reason for the reduction that “the circumstances in which [Woodward] acted were characterized by confusion, inexperience, frustration, immaturity and some anger, but not malice (in the legal sense) supporting a conviction for second degree murder.” See Keough, supra at 320 (affirming judge’s reduction to manslaughter where judge found “that the circumstances in which the defendant acted were characterized by fear, confusion, and anger, and that the necessary element of malice for second degree murder was absent”). We detect no error of law with regard to malice in this conclusion. A fine line distinguishes murder based on the third prong of malice from the lesser included offense of involuntary manslaughter.14 “The difference between the elements of the third prong of malice *670and . . . involuntary manslaughter lies in the degree of risk of physical harm that a reasonable person would recognize was created by particular conduct, based on what the defendant knew. The risk for the purposes of the third prong of malice is that there was a plain and strong likelihood of death. . . . The risk that will satisfy the standard for . . . involuntary manslaughter ‘involves a high degree of likelihood that substantial harm will result to another.’ ” Commonwealth v. Sires, 413 Mass. 292, 303-304 n.14 (1992), quoting Commonwealth v. Welansky, 316 Mass. 383, 399 (1944).
Although evidence of a single blow to a child of tender years may be sufficient to support a jury finding of malice, Commonwealth v. Starling, 382 Mass. 423, 426 (1981), such an inference is not necessarily required by evidence even of repeated blows to a young child. Commonwealth v. Vizcarrondo, ante 392, 397-398 (1998). In all the reported murder and manslaughter convictions in Massachusetts involving the battery of young children there was compelling evidence of multiple injuries from repeated instances of caretaker abuse, not death caused by a single fatal blow. See, e.g., Commonwealth v. Day, 409 Mass. 719, 720-721, 723-726 (1991) (manslaughter conviction reversed on erroneous admission of “profile” testimony); Commonwealth v. Hutchinson, 395 Mass. 568, 573-575 (1985) (murder in the first degree affirmed).15 The Commonwealth did not claim that Woodward had ever abused or injured Matthew prior to the fatal injury.16 Where there was no evidence in this case of repeated caretaker abuse, the judge did not abuse his discretion in concluding that the jury verdict of murder was not proportionate with convictions in other cases, including those cases resulting in convictions of manslaughter rather than murder. See Gaulden, supra at 556 (whether jury verdict is “markedly inconsistent” with verdicts returned in similar cases *671is appropriate consideration in deciding rule 25 [b] [2] motion).17
This jury, of course, were given no option to find a lesser degree of culpability than malice sufficient to support murder. “[W]e have applied § 33E to reduce verdicts (or order new trials) when judges have omitted to charge on critical themes that might have affected juries and brought about different verdicts.” Commonwealth v. King, 374 Mass. 501, 508 (1978). This judge did not charge on an issue that might have brought a different verdict. To correct his own error, he could conclude that a verdict of manslaughter was more “consonant with justice” than letting the murder verdict stand. Keough, supra at 320, quoting Commonwealth v. McCarthy, 375 Mass. 409, 416 (1978).
The judge suggested an alternative basis for reaching a manslaughter conviction, one that credited Woodward’s experts, in part, on the causation of Matthew’s injury. Under this view of reconciling the conflicting evidence on causation, Matthew had a preexisting skull fracture and blood clot, and Woodward handled Matthew “roughly,” which caused the clot to “re-bleed,” leading to his death. Weighing the evidence in such a way would permit the jury, had they been given the option, to find that Woodward committed a battery, fatal because of Matthew’s condition at the time, but not because of a severe blow by Woodward, and thus without malice sufficient for murder. We need not concur with this or any other view of the evidence on causation in order to defer to the judge’s discretion so to weigh the evidence and reach his decision that the evidence as a whole “comported more closely” with manslaughter than with murder.18 Keough, supra at 320, quoting Commonwealth v. McCarthy, 375 Mass. 409, 416 (1978).
*672Finally, we comment on the Commonwealth’s criticism of the judge for overstepping his role. This criticism depends on, but goes beyond, the Commonwealth’s more specific objections to the judge’s refusal of the manslaughter instruction and his verdict reduction. Those actions, in combination, appear to the prosecution to have manipulated the trial’s outcome and marginalized the jury, all to Woodward’s benefit. The Commonwealth’s argument is not frivolous.
Jurors bring the unique perspective of laypersons, representing the wider community’s judgment of a defendant’s degree of culpability, if any, for her actions. “The importance that our system attaches to trial by jury derives from the special confidence we repose in a ‘body of one’s peers to determine guilt or innocence as a safeguard against arbitrary law enforcement.’ Williams v. Florida, 399 U.S. 78, 87 (1970). It is this safeguarding function, preferring the commonsense judgment of a jury as a bulwark ‘against the corrupt or overzealous prosecutor and against the compliant, biased, or eccentric judge,’ that lies at the core of our dedication to the principles of jury determination of guilt or innocence.” Johnson v. Louisiana, 406 U.S. 356, 373-374 (1972), quoting Duncan v. Louisiana, 391 U.S. 145, 156 (1968). The integrity of the process by which we determine guilt may be jeopardized if the special confidence that the public bestows on a jury’s verdict is undermined.
We do not penalize the defendant for the error by the judge in this trial. See Commonwealth v. Millyan, 399 Mass. 171, 188 (1987). We uphold this judge’s reduction in verdict because, from our reading of the transcript and our review of all other reported murder and manslaughter convictions involving the battery of young children, we conclude that the judge acted within his discretion in determining that a conviction of manslaughter was more consonant with justice than a conviction of murder.
*673II. The Defendant’s Appeal
Woodward argues eight issues, only two of which need concern us: if we affirm the judge’s verdict reduction and sentence, she waives all claims that seek a new trial, the appropriate relief were we to agree with Woodward on any of her other six claims of error.19 We address and reject her claims seeking dismissal of the indictment or a required finding of not guilty.
1. The loss or suppression of evidence. Woodward requests the “drastic remedy” of dismissing the indictment, Commonwealth v. Lam Hue To, 391 Mass. 301, 314 (1984), due to the claimed failure of the Commonwealth to provide her access to potentially exculpatory evidence, and due to the loss of potentially exculpatory tissue obtained during the autopsy by the medical examiner. Woodward’s defense relied substantially on a theory that Matthew suffered from a previous head injury, incurred some weeks prior to his death, that began to bleed again on the fateful day of his hospitalization.20 The unavailable physical evidence that may have proved useful to this theory *674includes a clot of blood (fatal subdural hematoma)21; the skull fracture22; two sections of dura23; and subgaleal (scalp) tissue.24 Our cases concerning the Commonwealth’s failure to disclose or preserve exculpatory evidence have not considered the special circumstances attendant on a defendant’s request for *675access to, and the Commonwealth’s responsibility for preserving, physical evidence from a homicide victim’s body. We review briefly the circumstances of Woodward’s claims.
Dr. Gerald Feigin conducted an autopsy on February 10, 1997. The body was sent to Worcester for further radiological testing on February 11, and was released to Matthew’s family on February 13. On February 11, Woodward filed a motion in the Newton Division of the District Court Department for an “independent,” second autopsy by her medical experts.25 That motion was denied. A second, contemporaneous motion that “all evidence in the possession, custody, or control of the Commonwealth concerning this case be preserved and that no further scientific testing be performed without first notifying [the defendant]” was allowed in part by the judge; he ordered the Commonwealth to preserve all evidence acquired by the medical examiner, but declined to prohibit further testing without notice to Woodward.26 Woodward challenges the motion denying a second autopsy. She also contends that the Commonwealth suppressed exculpatory evidence when the Commonwealth did not disclose to her the existence of a fracture in Matthew’s skull in a sufficiently timely way to enable Woodward’s expert to investigate the age of the fracture. We first address these issues.
General Laws c. 38, § 4, authorizes the medical examiner to take jurisdiction of a body and perform an autopsy when he is of the opinion that a death was “due to violence.” After investigation or examination by the medical examiner’s office, “the body shall be released to the person with the proper legal authority to receive it, including the surviving spouse, the next of kin, or any friend of the deceased, who shall have priority in the order named.” G. L. c. 38, § 13. While we do not interpret this statute to prohibit in all circumstances a request such as the defendant’s, the statute’s silence on this issue certainly does not support any statutorily based right of a defendant to have access to a victim’s body for an independent autopsy. Rather, the statute’s explicit acknowledgment of a legal right of others to the body after the medical examiner completes his duties indicates that whatever due process right a defendant may claim *676must be balanced against statutory, as well as common-law and constitutional, rights to the body of a victim’s immediate family.
Another consideration also constrains a defendant’s unlimited access for purposes of a second autopsy. Autopsy procedures are inherently destructive, making second autopsies to some extent impracticable. The medical examiner, statutorily independent of law enforcement agencies, is charged with the responsibility of developing objective information as to a cause of death, and must, on request, provide a defendant charged in a death with a copy of the autopsy report. G. L. c. 38, § 7. We conclude that given these considerations, a defendant should show cause and specific need in a motion for access to a victim’s body. Here, the defendant’s written motion on its face did not articulate a specific need for the second autopsy. At the hearing, on questioning from the judge, Woodward did not claim that there was anything wrong with the autopsy performed by the medical examiner.27 She did argue that a second autopsy was needed to give her adequate time to prepare her defense and allow an expert to prepare testimony.28 Offsetting these concerns, the judge appropriately acknowledged the interests of Matthew’s family. Unlike most physical evidence, neither the courts nor the parties, without substantial reasons, may hold a homicide victim’s body for a prolonged period of time. Given the lack of specificity in Woodward’s articulated need for the second autopsy, it was not error for the judge to deny Woodward’s autopsy request.29
Woodward also contends that the Commonwealth should
*677have disclosed to her the existence of a skull fracture before Matthew’s body was released for burial. Woodward’s motion for an evidentiary hearing on missing tissue is silent on the skull fracture and she did not press at oral argument for relief on her contention that release of the skull for burial after completion of the autopsy constituted prejudicial loss or destruction of evidence.30 Unlike her claim on the lost dura tissue, she did not seek preclusion of Commonwealth testimony on the skull fracture, much less the drastic remedy of exhumation that she now proposes to us. Woodward has not established her claim of prosecutorial misconduct in the Commonwealth’s failure to inform her of the skull fracture until her murder arraignment hearing on February 13, 1997. There is nothing that we can detect to suggest that the Commonwealth had considered what forensic pathology evidence was critical for either the prosecution or the defense before the arraignment. In any event, we need not resolve this issue where it was not “fairly raised” below. Commonwealth v. Garcia, 409 Mass. 675, 678-679 (1991), and cases cited. These same considerations apply to her claims concerning the failure of Dr. Feigin to preserve any of the tissué evidencing hemorrhage in the scalp close to the fracture site: they were not “fairly raised” below.
Woodward also claims relief from the loss of potentially exculpatory evidence obtained during the autopsy. We focus on the “missing” sections of dura.31 When Dr. Jan Leestma, an expert for Woodward, examined the dura, he discovered that sections of the dura were missing. The judge held a pretrial *678hearing on this issue.32 Dr. DeGirolami, the Commonwealth’s neuropathologist, testified that he had not been informed by the medical examiner’s office or anyone else of the physical evidence preservation order. Following this hearing, the judge made a finding that the tissue had been lost, but that the loss was not an act committed in bad faith in an attempt to suppress evidence. He ruled that the loss did not justify dismissal of the case because it was not “so critical to the defense as to make a criminal trial fundamentally unfair.” Commonwealth v. Henderson, 411 Mass. 309, 311 (1991), quoting Arizona v. Young-blood, 488 U.S. 51, 61 (Stevens, J, concurring). We find no error in the judge’s ruling.
The Commonwealth’s obligation to preserve exculpatory evidence “grows out of [its] duty to disclose ‘evidence favorable to an accused upon request . . . where the evidence is material either to guilt or to punishment.’ ” Commonwealth v. Sasville, 35 Mass. App. Ct. 15, 19 (1993), quoting Brady v. Maryland, 373 U.S. 83, 87 (1984). A defendant is entitled to relief “for the Commonwealth’s failure to preserve [evidence] if [she] establishes a ‘reasonable possibility, based on concrete evidence rather than a fertile imagination,’ that access to the [evidence] would have produced evidence favorable to [her] cause.” Commonwealth v. Neal, 392 Mass. 1, 12 (1984), quoting State v. Michener, 25 Or. App. 523, 532 (1976). We have no doubt that Woodward met the threshold showing that there was a “reasonable possibility” that the missing evidence would be favorable to her.33
“[W]hen potentially exculpatory evidence is lost or destroyed, a balancing test is employed to determine the appropriateness and extent of remedial action. The courts must weigh the culpability of the Commonwealth, the materiality of the evidence and the potential prejudice to the defendant. . . . Our *679test does not require the Commonwealth to prove good faith or earnest efforts to preserve the evidence.” Commonwealth v. Olszewski, 401 Mass. 749, 755 (1988), S.C., 416 Mass. 707 (1993), cert. denied, 513 U.S. 835 (1994), quoting Commonwealth v. Willie, 400 Mass. 427, 432 (1987). On the first prong of this test, evaluation of the Commonwealth’s culpability for loss of potentially exculpatory evidence, had Dr. DeGirolami been made aware of the judicial order on evidence preservation, he could have ensured conscientious compliance to the extent feasible, in one way or another. Dr. DeGirolami is not at fault for any loss. But the failure to communicate to Dr. DeGirolami the importance of preserving tissue obtained from the body, in light of the very specific court order,34 is a failure of duty amounting to negligence by the medical examiner.
We recognize that the prosecutor’s responsibility for the negligence of the medical examiner’s office is more attenuated than its responsibility for loss or suppression of evidence by law enforcement personnel.35 “Ordinarily the prosecutor’s obligation to disclose information is limited to that in the possession of the prosecutor or police.” Commonwealth v. Donahue, 396 Mass. 590, 596 (1986), quoting Commonwealth v. Liebman, 379 Mass. 671, 675 (1980), S.C., 388 Mass. 483 (1983). But “[t]he prosecuting attorney’s obligations . . . extend to material and information in the possession or control of members of his staff and of any others who have participated in the investigation or evaluation of the case and who either regularly report or with reference to the particular case have reported to his office.” Commonwealth v. St. Germain, 381 Mass. 256, 261-262 n.8 (1980), quoting ABA Standards for Criminal Justice, Standards Relating to Discovery and Procedure Before Trial 2.1(d) (Approved Draft 1970). The medical examiner is such a person. The Legislature contemplated coordination of efforts between the medical examiner and the district attorney in investigation of deaths where criminal violence appears to have taken place. See G. L. c. 38, §§ 1, 4, 5. Particularly in light of the court order, the medical examiner, a Commonwealth agent, was accountable for preserving the dura tissue samples.
*680On the second prong of the test -— materiality of the lost evidence — we conclude that the missing right side section of dura was material to Woodward’s theory of the cause of Matthew’s death. As for the third prong of the test — the prejudice to the defendant from the loss of evidence — we are not persuaded that the degree of prejudice is so great as to warrant dismissal of the indictment. The jury heard an abundance of evidentiary detail on, and medical opinion endorsing, Woodward’s theory from Dr. Leestma, based on his examination of sections of dura covering areas other than that over the fatal hematoma. The jury also heard from Woodward’s other expert medical witnesses, relying on a significant amount of other medical and autopsy data, who gave opinions endorsing Woodward’s theory of the cause of death. The lost right side section of dura was an important piece of potentially exculpatory evidence, but may well have been cumulative of other forensic evidence marshaled by Woodward’s experts. The loss of evidence in this case was not so overwhelmingly prejudicial as in other cases in which lost evidence was uniquely critical. See, e.g., Commonwealth v. Henderson, supra at 311 (police officer’s writing of victim’s description of assailant lost); Commonwealth v. Olszewski, supra at 752-753 (numerous items lost from crime scene, victim’s autopsy, and victim’s vehicle); Commonwealth v. Gliniewicz, 398 Mass. 744, 748 (1986) (pieces of boots, showing minute traces of blood linking defendant to murder, destroyed during serological testing); Commonwealth v. Sasville, supra at 18, 29 (fetal tissue from rape complainant’s abortion, available for genetic marker testing as evidence of identity of rapist, destroyed at Commonwealth’s direction). Of these cases, we affirmed dismissal of an indictment in Henderson, supra at 310. The Appeals Court in Sasville, ruling that the culpability of the Commonwealth “amounted to a rare case of gross negligence and, in fact, comes perilously close to supporting an inference of bad faith,” reversed the judgment below and ordered the indictment dismissed. Sasville, supra at 24, 29. In Olszewski, supra at 750, and in Gliniewicz, supra at 745, we did not order dismissal of the indictments, but remanded for new trials. Neither the Commonwealth’s culpability nor the prejudice to the defendant is as great here as in those cases.
We agree with the judge that the loss of the dura evidence did not justify dismissal of the indictment against Woodward. “Absent egregious misconduct or at least a serious threat of *681prejudice, the remedy of dismissal infringes too severely on the public interest in bringing guilty persons to justice.” Commonwealth v. Cinelli, 389 Mass. 197, 210, cert. denied, 464 U.S. 860 (1983). In light of Woodward’s request that we not remand for retrial, we need not reach the question whether the judge’s failure to exclude testimony presented by the Commonwealth relevant to the missing dura tissue would be ground for reversing the manslaughter conviction and remanding for retrial. For similar reasons we conclude that the medical examiner’s negligence in failing to produce in a timely way the two closer, more sharply focused photographs of the skull fracture and the prejudice from their belated availability to Woodward were not so great as to justify dismissing the indictment. In response to the admittedly belated delivery of the photographs to Woodward, she requested only that she be allowed to recall two of her experts, relief that the judge granted in part.36 Her expert testified that the photographs provided important confirming evidence that the skull fracture was weeks old. In his ruling on Woodward’s posttrial motion, the judge noted that this testimony was “the last word on the photographs and the conclusions to be drawn from them,” and correctly determined that Woodward had not been prejudiced by the late disclosure.
2. Conclusiveness of scientific evidence on healing. Woodward also asks that we reverse her conviction and remand for a required finding of not guilty. We consider this request in two ways: as a request for review of the judge’s denial of her motion for a required finding of not guilty and, as Woodward urged in oral argument, a claim that her expert’s testimony at trial — evidence of healing processes37 — unrebutted by the Commonwealth, conclusively establishes that Matthew’s fatal *682injury occurred weeks before the day of his hospitalization and precludes a guilty verdict.
Our standard of review on motions for a required finding of not guilty is, considering the evidence in the light most favorable to the Commonwealth, “whether any rational trier of fact could have found the essential elements of the crime beyond a reasonable doubt.” Commonwealth v. Cordle, 412 Mass. 172, 175 (1992). As the judge pointed out, to reach a guilty verdict the jury had to conclude that the Commonwealth had proved its case beyond a reasonable doubt and, considering Woodward’s defense, “spumed as not worthy of belief, professional opinions emanating from a corps of highly-qualified, authoritative experts, [but] such dismissal is unquestionably within the jury’s province.” The Commonwealth presented its own qualified experts, including many of the treating physicians, who concluded that Matthew’s fatal injury was caused on the day of his hospitalization. The Commonwealth also effectively cross-examined Woodward’s medical experts. Viewing this evidence, as we must, in the light most favorable to the Commonwealth, the judge did not err in denying Woodward’s motion. See Cordle, supra; Commonwealth v. Latimore, 378 Mass. 671, 676-679 (1979), S.C., 423 Mass. 129 (1996).
Woodward also presses us to take judicial notice of the validity of and conclusive proof inferred from Dr. Leestma’s “crucial finding of periosteum dislodged from the fracture in the dura.” This finding “alone,” she argues, “proved” that the skull fracture was weeks old.38 Woodward did not ask the judge to take judicial notice of this “conclusive” scientific evidence. She did, however, argue that the judge consider this issue as grounds for her postverdict motion for a required finding of not guilty. Because the claim for judicial notice was not seasonably raised below, we need not reach it here. We decline, in any event, either on review of the judge’s denial of a required finding of not guilty, or based on taking judicial notice ourselves of scientific evidence of the age of Matthew’s head injury,39 to set aside Woodward’s conviction. She cites us no other similar case *683in which a lower court judge, much less an appellate court, has so credited such evidence.
III. The Sentence
Because we decline to grant the principal relief requested by the Commonwealth — reinstatement of the jury verdict — we consider the Commonwealth’s request that we set aside the sentence imposed, and resentence Woodward ourselves or remand the case to the Superior Court for resentencing by another judge. The Commonwealth seeks to avail itself of these remedies under G. L. c. 211, § 3, our general superintendence power. The relief requested has no precedent. It is settled law that the task of imposing the sentence on a defendant convicted of a crime rests with a judge in the trial court. It is not our role to enter an order modifying or adjusting a sentence. If a sentence is unlawful, we set aside the imposed sentence and remand the case to the trial judge for appropriate resentencing. See Commonwealth v. Coleman, 390 Mass. 797, 804 (1984); Commonwealth v. Franks, 365 Mass. 74, 81-82 (1974). The Commonwealth, in its request for one form of alternative relief — that we take it upon ourselves to resentence Woodward — provides no reason why we should depart from this well-settled principle.
As a second form of alternative relief, the Commonwealth asks that we remand the case for resentencing of Woodward by another judge in the Superior Court. That relief is also not available to the Commonwealth for multiple reasons that the dissent ignores. To begin with, our review of criminal sentences is limited. “We recognize that it is not within the power of this court to review an otherwise lawful sentence. This authority is delegated to the Appellate Division of the Superior Court . . . .” Commonwealth v. Coleman, supra. See Commonwealth v. Franks, supra at 81 (lawful sentence is one “which is within the limits of the applicable statutory provisions”).
*684Our review of a defendant’s sentence at the request of the Commonwealth is exceedingly rare.40 We have allowed such appeals and remanded for resentencing only in the procedural circumstances when a judge has granted a defendant’s post-sentencing motion, pursuant to Mass. R. Crina. R 29, 378 Mass. 899 (1979), to revise or revoke a sentence originally imposed, and the Commonwealth has sought reimposition of the original sentence. See Commonwealth v. Barclay, 424 Mass. 377, 379-380 (1997); Commonwealth v. Cowan, 422 Mass. 546, 547 (1996); Commonwealth v. Amirault, 415 Mass. 112, 115 (1993).41 We have found statutory authority for Commonwealth appeals in that Une of cases by broadening our construction of G. L. c. 278, § 28E (appeals by Commonwealth). Amirault, supra at 113-115. That statute, section 28E, until amended by St. 1979, c. 344, § 45, and construed in Commonwealth v. Therrien, 383 Mass. 529, 534 (1981) (upholding Commonwealth’s right to appeal from a postverdict finding of not guilty pursuant to Mass. R. Crim. P. 25 [b] [1], 378 Mass. 896 [1979]), and in Commonwealth v. Gaulden, 383 Mass. 543, 550 (1981) (upholding Commonwealth’s right to appeal from verdict reduction pursuant to rule 25 [b] [2]), had been interpreted to authorize the Commonwealth’s appeals only from pretrial motions. See Commonwealth v. McCarthy, 375 Mass. 409, 413 (1978). In Therrien, supra at 535, we sounded a note of caution that double jeopardy principles require that the allowance of certain post-*685trial defense motions “must be treated as terminating the criminal prosecution without any right to appeal.” General Laws c. 278,-§ 28E, of course, provides no basis on which the Commonwealth can appeal from a sentence that has not been revised or revoked at the request of a defendant, and there is no rule of criminal procedure that permits the Commonwealth to take such an appeal.
We may not vacate a sentence such as we have here, that was within statutory limits, because it appears too lenient or too harsh.42 We do not vacate a sentence unless we have been able to identify clear legal error in the sentence, and certainly not because of a “sense of unease that permeated the proceedings.” Post at 691. When asked to remand cases to increase defendants’ sentences, our jurisprudence confines us to cases of clear and identifiable error in the sentence itself, for the most substantial reason — our fundamental common-law traditions and constitutional principles of double jeopardy.
Under the common law, as recognized by our cases for more than one century, a trial judge, and a trial judge only, could increase a defendant’s sentence if, and only if, “no action had been taken under the original sentences, such as delivering [the defendants] to the house of correction to commence their terms,” in other words, “so long as it remained unexecuted . . . .” District Attorney for the N. Dist. v. Superior Court, 342 Mass. 119, 121, 123 (1961) (clarifying common-law rule to allow reduction of a defendant’s sentence after execution), relying on Commonwealth v. Weymouth, 2 Allen 144, 147 (1861).43 A common-law rule is not absolute, and this rule has been *686qualified by statutory developments.44 See Commonwealth v. Therrien, 383 Mass. 529, 532 (1981); Fine v. Commonwealth, 312 Mass. 252, 255-256 (1942). It nonetheless has been important in constitutional interpretation of double jeopardy principles.45
In Federal criminal cases, constitutional double jeopardy principles limit the prosecution’s right to appeal sentences to those cases explicitly authorized by statute; such statutes limit the scope of and narrowly focus such prosecution appeals. United States v. DiFrancesco, 449 U.S. 117, 136 (1980); United States v. Scott, 437 U.S. 82, 84-85 (1978). States risk offending the double jeopardy clause of the Fifth Amendment to the United States Constitution, made applicable to the States through the Fourteenth Amendment to the United States Constitution, see Benton v. Maryland, 395 U.S. 784, 795-796 (1969), if State appellate courts, absent explicit and properly limited statutory authority, review otherwise lawful sentences appealed by prosecutors. See Pennsylvania v. Goldhammer, 474 *687U.S. 28, 30-31 (1985); DiFrancesco, supra at 138-139. “It is clear from DiFrancesco and Goldhammer that when a sentence is increased in a second proceeding ‘the application of the double jeopardy clause . . . turns on the extent and legitimacy of a defendant’s expectation of finality in that sentence. If a defendant has a legitimate expectation of finality, then an increase in that sentence is prohibited ....’” Jones v. Thomas, 491 U.S. 376, 394 (1989) (Scalia, J., dissenting), quoting United States v. Fogel, 829 F.2d 77, 87 (D.C. Cir. 1987). DiFrancesco, supra, makes clear that the “extent” of a defendant’s expectation of finality is limited only when a statute specifically authorizes prosecution appeals of sentences. Our authority under G. L. c. 211, § 3, contains no explicit statutory authority to review sentences at the request of the Commonwealth, and no other statute otherwise authorizes review in these circumstances.
The “legitimacy” of a defendant’s expectation of finality in a sentence is, of course, undercut when a sentence is unlawful. Contrary to the dissent’s characterization, the Commonwealth makes no claim that the sentence imposed on Woodward is unlawful. The Commonwealth concedes that the sentence imposed falls within the broad range of punishment established by statute for a manslaughter conviction. See G. L. c. 265, § 13. Pressed several times at oral argument, the Commonwealth refused, perhaps out of respect for our jurisprudence on sentencing, to argue for consideration of the lawfulness of the sentence on any ground independent from its claim of error on the judge’s postverdict reduction of Woodward’s crime to manslaughter. In the procedural posture of this appeal, the only legitimate way to arrive at an increase in Woodward’s sentence is to conclude that error prejudicially infected the judge’s decision to reduce the verdict, reinstate the original conviction of murder in the second degree, and remand the case to the Superior Court for imposition of the statutorily mandated sentence.46 But, the dissent finds no error in the judge’s postverdict reduction of Woodward’s crime to manslaughter.
*688The dissent suggests that the sentence should be reconsidered because it is “tainted by legal error.” Post at 694. Remanding on such a basis to increase a sentence would mark a dramatic departure from our case law and the constitutional principles relevant to increasing sentences on the Commonwealth’s appeal. We have never vacated a sentence for the procedural “taints” identified by the dissent: an expedited sentencing hearing and the possible resulting unavailability of the victim’s family to provide a second set of victim impact statements, time constraints on yet further prosecution argument, or the failure of the record to reflect factors and sentencing goals considered by the judge in deciding Woodward’s sentence. Sentencing proceedings not infrequently have some or all of these features, as the dissent recognizes. Post at 692 n.2. Here, the Commonwealth acceded to the hearing as scheduled, as the dissent also recognizes, did not ask for a continuance for its own sake or in order for Matthew’s family to be in attendance,47 and articulated sufficient reasons for the sentence that it recommended. The Commonwealth’s time to prepare for argument on sentencing was not limited to the hours between the morning release of the judge’s order reducing the verdict and the sentencing hearing scheduled for that afternoon. It had ample opportunity to prepare during the six-day interim between the hearing on the posttrial motion and the release of the judge’s order, when the only remaining matter to be addressed was resentencing, in the event that the Commonwealth lost on Woodward’s posttrial motion. Nor can one conclude from the expedited sentencing hearing that the judge had failed to deliber*689ate fully his sentencing decision in light of the abundant information available to him concerning the defendant and the victim’s family before and during the course of this most amply explored case. We also do not draw any adverse conclusion from the sparseness of the record of the sentencing decision: we do not require a judge to give reasons for a sentence. See Commonwealth v. Banker, 21 Mass. App. Ct. 976, 979 (1986). None of the alleged flaws in the sentencing proceeding vitiates the sentence singly. Only by the addition of something ineffable to the sum of these alleged flaws does the dissent suggest impropriety of the sentence, but that ineffable something is not identified.
The dissent also intimates that, because Woodward asked that the jury not receive a manslaughter instruction, the sentence for manslaughter imposed by the judge is inappropriate. We do not limit, a judge’s postverdict discretion to correct injustice because it may have been brought about due to a defendant’s trial strategy, unsuccessful in hindsight. See, e.g., Commonwealth v. Millyan, 399 Mass. 171, 188-189 (1987) (failure of defendant to request intoxication instruction because it was inconsistent with trial strategy did not preclude verdict reduction, in light of evidence of intoxication); Commonwealth v. Franks, 365 Mass. 74, 82 (1974) (failure of defendant to except to judge’s charge to jury does not preclude court from vacating sentence imposed for crime not committed).
Finally, we have criticized the judge for his error in acceding to Woodward’s request not to give a manslaughter instruction. His ruling did have a basis in our cases, for we have declined to penalize defendants who adopt an “all-or-nothing” strategy.48 His ruling does not suggest, nor does the dissent imply, that the judge committed a legal error purposefully to favor Woodward. There is no complaint about his day-to-day handling of this lengthy and complex trial.
The Commonwealth’s only argument that conceivably could be interpreted as grounds for revisiting Woodward’s sentence is that, in reducing Woodward’s verdict and sentence, the judge must have found that Woodward had committed “no crime,” and that the judge “converted” her conviction of murder to an “acquittal.” That interpretation of the judge’s actions is not convincing. We have noted that the judge on a rule 25 (b) (2)
*690motion need not draw the same conclusions from the evidence as did the jury. See Commonwealth v. Keough, 385 Mass. 314, 319-320 (1982); Commonwealth v. Gaulden, 383 Mass. 543, 555 (1981). But this judge, in reducing this jury’s verdict to manslaughter, must have accepted the jury’s finding that Woodward’s actions caused Matthew Happen’s death; he had the option to, but did not, order the entry of a finding of not guilty. Mass. R. Crim. R 25 (b)' (2). Having had the opportunity to view all the witnesses face-to-face, including Woodward who testified, he concluded that Woodward was guilty of a most serious crime — for manslaughter is such a crime. We do not view the judgment against Woodward as a light matter. She stands guilty of causing an infant’s violent death. The outcome of this criminal trial most assuredly was not an “acquittal.”
The dissent claims that this case is exceptional. It is not. Judges do reduce jury verdicts to some lesser degree of crime. The law permits them to do so. Judges regularly sentence defendants to time served. The law permits them to do it. What would be exceptional is the disposition urged by the dissent. Whatever the scope of our powers, it does not allow us to act on the basis of impressions and characterizations that have no correlate in acknowledged rules or doctrines. It is the essence of the rule of law that exceptions that burden defendants not be made unless justified by some rule or principle that we would be willing to follow in other cases.
Because the sentence imposed by the judge is lawful, we decline to remand the case for consideration of an increase in the defendant’s sentence. The conviction of manslaughter, together with the sentence imposed, shall stand. The Commonwealth’s petition for G. L. c. 211, § 3, relief and the defendant’s motion to dismiss the Commonwealth’s petition are remanded to the county court for entry of an order denying the relief sought by each. The actions of the Superior Court judge in reducing the conviction of the defendant and sentencing her to the time deemed served are affirmed.
So ordered.