Continuity mistake: At the very end of the episode when Nina Sharp exits the elevator, she mostly steps out of the elevator completely before the masked men come and shoot her. However, when they review the security footage of the attack in the next episode, "There's More Than One of Everything," you see that she barely takes a step before being shot. (00:49:15)
Continuity mistake: When Olivia crosses over to the other side you see people wearing FBI jackets. But according to later episodes that had changed to Fringe Division on the other side years earlier.
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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