Other mistake: The FBI agents call for a taxi and official transportation from the Evans apartment and gave the address of 963 North Gilbert. However, the Evans lived at 921 North Gilbert. Since the FBI was at their apartment, you would think that they would know the address or exactly where they are in a Chicago project. (00:13:03 - 00:28:29)
Other mistake: JJ says that everybody else in the office just has to look at their watch when the boss asks them the time but he has to go outside down the block because he can't afford a watch. Throughout the whole scene, you can see a wristwatch on his right wrist. He even raises his arm where his sleeve moves to his elbow to show it. It looks like a pretty expensive watch too. (00:05:00)
Answer: Could have very well been that he did have a speaking part, but ended up on the cutting room floor, and they just didn't fix the credits.
ckbyers