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

After making a big return, we suspiciously haven't heard anything from Noel. Why is he back? It seems like he's working with Jenna, but we don't know if he has any allegiance to Sara. Maybe Jenna grew suspicious of Sara but had Noel do her dirty work for her. Maybe he is double crossing them and has gone rogue. Either way, he's worth keeping an eye on.