Defendant David Powell was convicted on three counts of violating 18 U.S.C. § 2314 and on six counts of falsely certifying automobile odometer readings in violation of § 15 U.S.C. §§ 1988(b) & 1990c, and 18 U.S.C. § 2 (the “false certification” counts). On appeal he argues that the trial court erred in admitting certain evidence and in not entering a judgment of acquittal on the false certification counts. We conclude that if the trial court erred in its evidentiary rulings, the error was harmless and insufficient to justify reversal on any count. But we agree with the defendant that he was entitled to an acquittal on the false certification counts. We thus affirm all the defendant’s convictions under § 2314 and reverse his convictions on the false certification counts.
I.
The relevant facts can be simply stated. Powell was the sales manager of Colonial Car Company, a sole proprietorship owned by Robert Lyons. Colonial Car Company was engaged in the business of purchasing used automobiles from “Dealer” auto auctions and reselling them to used car retailers. All the counts alleged that Powell arranged the sale of various used cars, knowing that the odometers on the cars had been rolled back, and that he falsely certified that the odometer readings were accurate. The § 2314 counts involved the sale of used cars to an out-of-state car dealer, who paid for the cars by checks that traveled interstate. The false certification counts involved separate consignments of used cars to auto auctions. For each false certification count, the evidence showed that Powell signed, in the space designated “transferor’s signature (seller),” sales invoices showing false mileage readings. A jury convicted Powell on all counts.
II.
Powell first argues that the trial court committed reversible error by admitting a witness’ prior consistent statement and false odometer certifications that Powell signed subsequent to those for which he was indicted. We do not reach the issue of whether the rulings were erroneous because, even if they were, the error was harmless. If “it is more probable than not that the error did not materially affect the verdict,” then reversal is not required. United States v. Valle-Valdez, 554 F.2d 911, 915 (9th Cir.1977) (emphasis omitted). Here, the other evidence of Powell’s intent in the record is overwhelming. Moreover, the government introduced into evidence six false mileage certifications directly relating to the indictments; the chance that the jury might have been improperly influenced by the ones Powell objects to is remote. As Powell’s evidentiary challenges are the only grounds raised on ap*1423peal concerning the § 2314 counts, we affirm his convictions under § 2314.
III.
A person cannot violate § 1988(b), even if he willfully provides false mileage information to a transferee, unless he is a “trans-feror.” The regulations define a transfer- or as “any person who transfers his ownership in a motor vehicle.” 49 C.F.R. § 580.-3. Powell argues that he was not a trans-feror, and thus cannot be convicted under § 1988(b), because he never had an ownership interest in any of the cars sold with false mileage readings.
We agree with the defendant. Powell had held himself out as the owner of the vehicles at issue, arranged the sales, and signed the sales certificates as transferor, but was at all times merely an agent for the true owner, Colonial Car Company. He never had any legal or beneficial ownership interest in the vehicle. It is true that defendants have at times been held liable as transferors even if under the relevant state law they might not have been deemed to be the legal owners or to be transferring their ownership. See United States v. Ellis, 739 F.2d 1250 (7th Cir.1984); Tusa v. Omaha Auto Auction, Inc., 712 F.2d 1248 (8th Cir.1983); Goeman v. Keating, 498 F.Supp. 700 (D.S.D.1980). In all these cases, however, the transferors had some legal or beneficial ownership interest in the vehicles at issue. See Ellis, 739 F.2d at 1253 (legal title); Tusa, 712 F.2d at 1251-52 (legal title); Goeman, 498 F.Supp. at 701-02 (beneficial owner). These cases largely reflect the view that interpretation of §§ 1988 and 580.3 should be guided by a uniform nationwide standard of “ownership” that does not vary state by state depending upon what that state deemed to be the relevant indicia of ownership. See Ellis, 739 F.2d at 1254; Tusa, 712 F.2d at 1252. The cases thus merely stand for the proposition that persons who had certain legal or beneficial ownership interests in cars can be considered transferors for purposes of § 1988 even if they would not have been considered owners or transfer-ors at state law. The eases do not go so far as to include those who, like Powell, never had any legal or beneficial ownership interest in a transferred car.
Indeed, in the only case presenting a fact pattern similar to the case at bar, it was held that the president of a car dealership could not be the transferor of a car, despite the fact that he signed as the seller, because he never had any actual ownership interest in the car. Cwiakala v. Economy Autos, 587 F.Supp. 1462, 1465 (N.D.Ind.1984). Being the apparent owner and seller of a car is not enough to make one a transferor — one must have some legal or beneficial ownership interest in the car. See McGinty v. Beranger Volkswagen, 633 F.2d 226, 230 (1st Cir.1980); Ryan v. Edwards, 592 F.2d 756, 762 (4th Cir.1979).
The government argues that even if Powell was not a transferor he could be convicted under 15 U.S.C. § 1990c(a). That section criminalizes intentional violations of § 1988, among others, providing criminal penalties for “[a]ny person who knowingly and willfully commits any act or causes to be done any act that violates any provision of this subchapter.” The government reasons that Colonial Car Company, the transferor, violated § 1988(b) by furnishing false mileage certificates to the transferee through its agent, Powell. By intentionally furnishing mileage certificates he knew to be false, Powell thus “knowingly and willfully ... cause[d] to be done [an] act that violate[d]” § 1988, even though Powell could not, as a non-owner, have himself violated § 1988. Although certainly a viable theory, this argument was raised for the first time on appeal, and no basis for raising the argument appears anywhere in the record. The indictment and jury instructions refer to Powell as a transferor, with § 1990c included only as the provision that allows criminal penalties.
Alternatively, the government contends that the defendant could be convicted under 18 U.S.C. § 2 for aiding and abetting a crime against the United States. Powell contends that an aiding and abet*1424ting conviction cannot stand because the government has not introduced sufficient evidence to show that a principal committed a crime. The government correctly points out that a defendant can be convicted of aiding and abetting even if a principal is never identified or convicted. See United States v. Mehrmanesh, 689 F.2d 822, 835 (9th Cir.1982); United States v. Chenaur, 552 F.2d 294, 300 (9th Cir.1977); Feldstein v. United States, 429 F.2d 1092, 1095 (9th Cir.), cert. denied, 400 U.S. 920, 91 S.Ct. 174, 27 L.Ed.2d 159 (1970). Nonetheless, a defendant cannot be criminally convicted absent proof that a principal criminal offense was committed. See, e.g., United States v. Hurd, 642 F.2d 1179, 1182 (9th Cir.1981); United States v. Jones, 425 F.2d 1048, 1056 (9th Cir.), cert. denied, 400 U.S. 823, 91 S.Ct. 44, 27 L.Ed.2d 51 (1970); United States v. Ruffin, 613 F.2d 408, 412 (2d Cir.1979); United States v. Barker, 542 F.2d 479, 484 (8th Cir.1976). The fact that the principal need not be identified or convicted has never been thought to obviate the need for proof showing that an underlying crime was committed by someone. See United States v. Hudson, 717 F.2d 1211, 1214 (8th Cir.1983); United States v. Campa, 679 F.2d 1006, 1013 (1st Cir.1982); United States v. Perry, 643 F.2d 38, 45 (2d Cir.), cert. denied, 454 U.S. 835, 102 S.Ct. 138, 70 L.Ed.2d 115 (1981); United States v. Barfield, 447 F.2d 85, 89 (5th Cir.1971). Rather, courts in this circuit, as in others, continue to require evidence showing that a principal offense has been committed — including requiring evidence that some principal had the requisite intent — despite acknowledging that identification or conviction of the principal is not per se necessary. See United States v. Barnett, 667 F.2d 835, 841-42 (9th Cir.1982); Chenaur, 552 F.2d at 299-300. In this case, the prosecution has demonstrated that Powell had the requisite intent but made no showing that any person other than Powell, identified or otherwise, had the necessary intent to violate § 1990c.
AFFIRMED IN PART AND REVERSED IN PART.