Shaq: Tom Brady's Jersey Steal Was Inside Job ... Trust Me, I'm a Cop!!

Detective Shaq has joined the Tom Brady Super Bowl jersey investigation ... and he already has a theory -- INSIDE JOB!!!

FYI, Shaq has been a sworn reserve police officer with real law enforcement agencies in several states including California, Florida and Arizona. He even did some work with the Dept. of Justice.

So, with TB12's jersey still M.I.A. ... we asked Officer O'Neal (who was leaving the Oreo Dunk Challenge) if he had a hunch on who may have jacked the piece of Super Bowl history.

There's more ... Shaq also sets the record straight on his beef with his "Inside the NBA" co-star, Charles Barkley, and how things went down off camera following their heated exchange last week.