Travis,

Although in this case it appears the big reason the crooks can't be identified is because we don't know who they are, I'd argue if we did it's easy to identify them without fear of slander. Just use the construction "suspected" in mentioning the person and "alleged" in identifying their crime. I.E. "Many chippers suspect John Doe is selling altered brass core chips. Doe was allegedly seen by two chippers selling altered chips at the PS show."