Ian Thomas

As of the latest Episode, Ian Thomas commited suicide, leaving a note confessing he was the one to kill Alison. He is the father of Spencer's sister Melissa's baby, named Taylor. Though before Alison died, her and Ian were in a secret relationship. Alison then discovered that Ian had been filming the five of them, along with Jenna and Toby Cavanaugh, in secret. Ian then found out that Alison had the videos and could use them against him, so he killed her.

Add more! This was all I could think of. Thanks:)