Day 4: 8:00 A.M.-9:00 A.M. - S4-E2
Continuity mistake: When Agent Lobell tries to stop a car from leaving the train station, the terrorist in the car shoots at him through a window, shattering it. When the camera cuts to a shot of Lobell falling to the ground, the window in the car is gone, but no fragments of it are on the car or the ground under it.
Answer: According to Jack in season 5, Nina was "deep cover" before the pair ever met, so it's safe to assume she was recruited before she joined CTU. As for what her primary mission was, who knows? Perhaps it was to gather sensitive intel and pass it on to her superiors. Given that she worked for an intelligence agency, it's not a stretch. Or perhaps we may find out in season seven.
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