Dark Knight Question?...?

I suppose the best answer to this question would be "It's just a movie" and that i should suspend my disbelief. but i was just wondering. Near the beginning of The Dark Knight there's a scene in a courtroom where that mob guy pulls a gun on Harvey Dent. My question is, how would he have gotten a gun into a courtroom, you'd think the metal detectors and security guards would have caught him?