Continuity mistake: In the first basketball game in Venice Beach, Edward Furlong leans up on a fence and his school bag's strap slips off his shoulder. In the next shot, the strap is back up on his shoulder. Yet he had no time to fix it.
Continuity mistake: In the dinner scene with the whole family and the mother's new date they are talking about the LA riots when Edward Norton puts down his fork. It cuts to a shot behind him and he's still holding the fork up.
Continuity mistake: When Edward Furlong is called into the principal's office in the beginning of the film he picks up his school bag with his right arm, and then enters the office with it on his left arm. And there is no time in between for him to change arms.
Audio problem: At Cameron's party, when Derek is about to leave and Seth comes at him with a gun you can see Danny running down the stairs screaming at Seth, but his mouth doesn't move.
Visible crew/equipment: When Derek is running into the bathroom after Danny has been shot, as he is running through the crowd of students, it cuts to a shot from the side of the hallway, it's very quick, but you can see a camera, a cameraman, and the boom mike and its operator.
Answer: It's quite simple: He was one of them, a fellow skinhead. In prison different groups stick together for mutual protection and comradeship, and as neo-nazis/skinheads would be fairly unpopular with the colored inmates, all the more reason for them to protect each other.
Twotall