So the big question is who is the killer, but my guess is that the answer isn't even decided yet. The producers probably have several different endings planned out so that they can change it depending on the way fans take to certain characters which is the perk of it being a tv show. Also everyone should listen to noah as he states multiple times that we shouldn't focus on the killer but more on the stories that take place with the teenagers and the more important question whose next?
It's definitely two killers since every movie had two, and that is the only way you can see one character at the scene of the crime while the other one kills the victim.
