Continuity mistake: When Olivia says "Freshman", Peter and Walter are seen screw driving wires into Roy's head. In the next shot, the wires are gone and they are drilling in his head. Later on, they use the screwdrivers again. (00:36:30)
Trivia: Olivia walks past an observer on the train while looking for the suspect. (00:42:05)
Answer: In the time line of Season 4, William Bell is trying to destroy both universes to create a new one, and he needs Olivia to power the collapse. So he helped her escape. But the real question is, if not in search of Peter, why Olivia has to travel to the alternate universe to be captured and replaced?
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