Day 4: 2:00 P.M.-3:00 P.M. - S4-E8
Factual error: When Edgar proves that Mary-Ann Taylor framed Sarah to be the rat in CTU, he claims that she remotely took control of her computer by sending the signal over "a plain old AC power line." This is not possible, unless the computers were equipped with special hardware to separate the AC from the signal. If they were, this traffic would have been observed by James Heller's assistant.
Day 4: 12:00 A.M.-1:00 A.M. - S4-E18
Factual error: In the opening scene of the episode, Marwan gives a cohort Lat/Long coordinates for a nuclear missile. The computer shows these coordinates as being in the Midwest, they are actually in Nevada. (37 14' N 115 21' W).
Day 4: 9:00 P.M.-10:00 P.M. - S4-E15
Factual error: The bad guy uses the thumb to access the Air Force base at the end of the episode. Thumb scanners are activated by the pulse and wouldn't work otherwise.
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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