The reason all those FBI agents are swarming all over David Copperfield's warehouse in Las Vegas is that he has been accused of rape by a Seattle woman. She alleges that David Copperfield raped her while both were in the Bahamas, but didn't report it until she got back to Seattle. Because of that, Seattle police called in the FBI.
Rape is a horrendous crime and should be investigated thoroughly. However, there were 12 FBI agents who participated in the raid on the warehouse. Twelve federal agents accompanied by local police means either there is a bunch more going on here than a rape charge, or the Las Vegas FBI office had nothing better to do and thought they could all pay a visit to the warehouse known as the International Museum & Library of the Conjuring Arts which very few people have ever got to visit.
It seems that if this were strictly a rape case, you wouldn't even need to raid the warehouse unless the rape involved something from his act.