[Eric72]

If there's no security footage, here's an idea:

There were probably hundreds of people walking around with their phones. Some of them were likely shooting footage, either for social media or personal use. Others were taking pictures (still shots) for the same reasons.

Net54 has more than a few members (Mike Moynihan, for example) with YouTube Channels and other methods of reaching out to thousands of collectors without too much effort on their part. Have the Net54 community spread the word:

Hey, I'd like to ask my viewers to check on something. If you were at the Philly Show on xxxday and took some pictures or video at around xx o'clock, take a look at what you've got. You might have caught a criminal stealing from one of the dealers. If you've got footage or pictures...

There may be legal nuances involved with this; I don't know. However, I do know that the number of pictures and amount of footage can only go down as time passes. Plus, the show is fresh in people's minds right now. Carpe diem.