Other mistake: When Peter is watching Richard Steig in the interrogation room and gets up to go in there himself, he tells Walter to stay there. On the live video screens behind him, you can see Peter enter the room before he actually does. (01:03:50)
Visible crew/equipment: When Olivia spots John taking off in his SUV, the reflection of a crew member's head is visible when she opens the driver's side door. (01:13:35)
Continuity mistake: The front license plate on John's SUV falls off during the chase with Olivia. It reappears seconds later. (01:15:30)
Factual error: When the 747-aircraft of the fake German airline is being shown, you can see the German flag on the plane. But you also see an "N-xxxxx" registration which stands for USA. If it were a real German plane, it would have a "D-xxxx" registration.
Answer: He helped his father evade capture, impeding the investigation.