record below amply supports the trial judge's finding that the pennies were not true mint errors but had been artificially altered to appear multi-struck after they left the mint. The chief government witness, an Assistant Technical Consultant to the Director of the Mint, demonstrated in detail that it would have been physically impossible for the federal mint machinery to have produced the type of multiple impressions found on the Piacentile pennies. In addition, he testified that the coins were too large in diameter to have come from the mint but might have been enlarged by being restruck on some other press, and that the bulge on the tail side of the coins would be a natural result of striking the head after the coin had been removed fromits original die, but could not have been caused by multi-striking in the original. Although the defendants, neither of whom took the stand, produced four expert witnesses who testified that they thought the coins were genuine mint errors, none offered a satisfactory explanation of how the mint equipment could have produced the multiple strikes.


6
Piacentile argues that the conclusion that the coins were artificially altered was merely an "inference" and was impermissibly based on the opinions of the Government's witnesses, rather than on established facts. A persuasive showing that the multi-striking could not have been caused by the mint machinery, however, is substantial proof that they were tampered with after leaving the mint. The Government's expert witness presented a description of the technical operation of the mint as a