Chapter 15 - S2-E2
Corrected entry: While Lucas watches the footage of Zoe's death, the footage, seen frame-by-frame, only shows the moment where she "falls" onto the rails. Earlier footage however, would have shown her leaning on the wall, talking to someone (Underwood) on the other side. (00:07:00 - 00:08:00)
Correction: The footage would have shown her leaning against the wall, doing something on her phone (deleting the connection with Underwood) until she walked after him. It is also of a low quality, at a weird angle, and from far off, meaning they probably couldn't have even seen her talking. For all they know, she was waiting on the train. That is nowhere near enough to keep a case open.