We have on appeal the judgment and sentence of the trial court imposing the death penalty upon Derek Todd Thompson. We have jurisdiction. Art. V, § 3(b)(1), Fla. Const. We affirm the conviction, but vacate the death penalty and remand for imposition of a life sentence with no chance of parole for twenty-five years.
Sometime after midnight, May 3, 1992, Derek Thompson walked into a Subway sandwich shop in Pensacola, conversed with the attendant, Carl Lenzo, and then shot him once through the top of the head. Lenzo lost consciousness immediately and died. Marilyn Coltrain was eating a sandwich in her car in front of the shop and saw Thompson enter the shop and converse with the clerk. When Coltrain looked away briefly, she heard a “pop,” looked up, and saw Thompson standing over the clerk, who had been shot. She and Thompson looked directly at one another, and then she started her car and drove away.
Another witness, Edward Faulk, walked to within a few feet of the store and saw Thompson come out of the shop carrying a gun. Thompson pointed the gun at Faulk and then ran away. Officer James was within several blocks of the shop when he got a call regarding the robbery. He saw Thompson walking down the street, and because he matched the description broadcast over the radio, stopped him. James found $108 and the ammunition clip from a 9-mm pistol in Thompson’s pockets, and found a 9-mm pistol on the ground near where Thompson was standing. Officer James took Thompson back to the sandwich shop, where both Col-train and Faulk identified him.
Thompson was charged, tried, and convicted of robbery with a firearm and first-degree murder. During the penalty phase, the State put on two witnesses: a probation officer, who testified that Thompson was on community control at the time of the crime, and the victim’s mother, who described her son and the effect of his death on the family. The defense put on numerous witnesses, including Thompson’s father, sister, and wife, and many friends and acquaintances. The jury recommended death by a vote of nine to *826three on the first-degree murder count, and the judge imposed the death penalty, finding four aggravating circumstances1 and several nonstatutory mitigating circumstances.2 A consecutive twelve-year sentence was imposed on the robbery count. Thompson appeals his first-degree murder conviction and sentence of death, raising six issues.3
Thompson claims that the trial court erred in failing to grant a mistrial when the prosecutor, during closing argument, commented on the gun, bullet, and shell used in the murder. The prosecutor made the following statement:
[State’s expert] Mr. Love testified that [the] gun that is in evidence that was at the defendant’s feet is the murder weapon. He also indicated that the bullet, the shell and the gun are available for testing, anyone can repeat my test to determine whether or not—
Defense counsel objected, “By saying that, he’s indicating to the jury that we should have had to prove something, we should have had to go and get a ballistics expert, and that’s how they are going to read that.”
The court overruled the objection, but gave a curative instruction stating that Thompson is not required to prove anything. The prosecutor then repeated the gist of his earlier statement: “The expended shell and the gun are available for anyone to see and examine that wants to.” Thompson renewed his objection, which was overruled. Thompson claims that the court should have granted a mistrial. We disagree.
The prosecutor’s statement was not a comment on the defendant’s right to remain silent. The record shows that the prosecutor merely repeated what the State’s ballistics expert had testified to at trial:
Q. The tests that you performed on all these items, can they be reproduced?
A. Certainly.
Q. Another examiner wanted to come in and look at them, could he reproduce your results?
A. Yes, sir.
We note that defense counsel did not object to the expert’s testimony at the time it was originally presented. We find no error.
Thompson claims that the court erred in finding that the murder was committed in a cold, calculated, and premeditated manner. We agree. No one saw the actual shooting. The only witness in the immediate area, Marilyn Coltrain, was eating a sandwich in her car in front of the shop. She watched Thompson enter the store and converse with the clerk. She then looked away, heard a “pop,” looked up, and saw Thompson standing over the victim. A number of scenarios inconsistent with heightened premeditation are possible: The victim may have struggled with Thompson; the victim may have tried to duck and hide from Thompson; or the victim may have tried to escape. The record simply does not show what happened in the brief time span when the witness looked away. We strike this aggravating circumstance.
Thompson next claims that the trial court erred in finding that the murder was committed to eliminate a witness. We agree. ‘We *827have long held that in order to establish this aggravating factor where the victim is not a law enforcement officer, the State must show that the sole or dominant motive for the murder was the elimination of the witness.” Preston v. State, 607 So.2d 404, 409 (Fla. 1992), cert. denied, — U.S.—, 113 S.Ct. 1619, 123 L.Ed.2d 178 (1993). This was not shown beyond a reasonable doubt because again we do not know what happened during the time witness Coltrain looked away. We strike this aggravating circumstance.
Thompson claims that the court erred in finding that he was under sentence of imprisonment at the time of the crime. We agree. The trial court found as an aggravating circumstance that the “[¿defendant was under a community control sentence in two different eases, Number 87-1401 and Number 91-1720, when these offenses were committed.” After Thompson was sentenced to death in the present capital ease, however, the trial court in Case Nos. 87-1401 and 91-1720 granted Thompson’s motion to dismiss an affidavit of violation of community control in those two cases on grounds that the sentences had been erroneously imposed. The sentences in Case Nos. 87-1401 and 91-1720 were illegal.4
‘We have expressly held that a conviction used as an aggravating circumstance, which is valid at the time of the sentence but later reversed and vacated by an appellate court, results in an error in the penalty phase proceeding. The reversal eliminates the proper use of the conviction as an aggravating factor.” Long v. State, 529 So.2d 286, 293 (Fla.1988). We conclude that the same reasoning applies to an aggravating circumstance based on an illegal sentence. We strike this aggravating circumstance.
Having struck three aggravating circumstances, this leaves a single aggravating circumstance to support the death penalty, i.e., the murder was committed in the course of a robbery. We have in the past affirmed death sentences that were supported by only one aggravating factor, but those cases involved either nothing or very little in mitigation.” Songer v. State, 544 So.2d 1010, 1011 (Fla.1989) (citation omitted). The present case, in contrast, involves significant mitigation, as documented in the record.
Accordingly, we affirm Thompson’s first-degree murder conviction, but vacate the death penalty.5 We remand for imposition of *828a life sentence without possibility of parole for twenty-five years.
It is so ordered.
GRIMES, C.J., and OVERTON, SHAW, KOGAN and HARDING, JJ., concur.
WELLS, J., concurs in part and dissents in part with an opinion.