It was a set-up. The friends played a joke on the new kid, and as a result, he accidentally killed the teacher. He is taken down to the police station, but they let him go, because the police say that the teacher killed was the one that killed Becky at the start - the gun in his drawer used to shoot him was the one used to kill her. Dodger shows up, and says sorry. He figures out that she convinced the others to play the prank, and also figures out that the whole thing was a set-up, as Dodger killed Becky, and wanted the teacher dead for his betrayal too. She sort of admits it, but he has no proof.