There's Another Dead Body on Pretty Little Liars, but Who Is the Killer?

This is one of the least likely scenarios, because it looks like Archer's actually dead. Spencer and Hanna dig up his grave to double check and his body is very cold. But we've also had characters come back from the dead before. If Archer is still alive, then it's possible he's back to get revenge on all of those who know his true identity. Why not start with the weakest link?