Personally I think that Jade is the killer. I have always HATED her, >( so thats probably why I think this. But it seems like everything points to her. I mean, she hates Maddie, so if she kills people and make other people believe its Maddie, she can get her locked up and that way she'll never have to see her again. Then, she tried to kill Gwen, numerous times. She says she's in love with Will, but Will won't be with her because he loves Gwen. So if you get Gwen out of the way you can have Will all to yourself. I don't know, it's probably not but still I will forever believe that its her.