There is never any harm in asking. The one he had can be tracked by the serial number and it can easily be found. It may have been re-sold, but at least you checked. Perhaps someone noticed it and took it out. Who knows. The point is, it's worth checking. I highly doubt there will be any sort of law enforcement agents awaiting your return. That's just getting silly now.
On top of that, flash cards are legal in the US. The contents of the SD card, however, not usually.