Continuity mistake: When the film crew are making their movie in the tunnel, the short white guy is standing on some platform for a minute, and you can clearly see a member of the film crew in the background. Then they disappear.
Continuity mistake: When Trevor is showing Amy the search he entered into the computer, Vanessa and Toby are both on the list. Why was Vanessa on it when she hadn't been attacked yet, and why was Toby on it when he hadn't been attacked at all?
Continuity mistake: Considering how carefully the killer cleaned the scene of Sandra's death, how likely is it that he would have left a cigarette at the scene of Simon's death? He didn't know that Amy was on her way out, so he wouldn't have rushed away from the scene.