SPOILER: About the killer

So about the second killer.

It is strongly implied that Audrey is involved once turns out to have the letters and papers that were stolen, and that she escapes being killed in the finale when she is pinned down by the dressed killer and not to mention that her DNA was found inside the mask.

But I think she is a red herring, whatever she is hiding will probably be exposed in season 2. We also still don't know who did the killing in the past and we shouldn't rule out that this might be the same killer, Seth is also another possibility as the incident with his past and the dead student associated to it are still unclear.

There's one additional issue I have with Audrey being the second killer, she isn't tall enough to have been in the suit in any scene that was shot and there's no way she could carry or overpower someone like Will (the self defense thing is different because it's a move assisted by gravity and the hip works to propell momentum) or the sheriff, and I mean dragging or carrying someone that is almost twice your size.

Also, who captured Emma's mom? Piper was headed to the party and Audrey was already there.