Lorelei Martins is not dead. She is with RJ, on or against her will.

Rosalind Harker has something to do with the killings. She knows more then she tells.

Kristina Frye might be involved somehow. Her disappearance was strange. Although, last time she was seen in the CBI, talking with Jane, so they wouldn't just let her go like that. They're probably keeping her somewhere. (mental inst, etc).   

Gale Bertram and Bob Kirkland have nothing to do with RJ. Think they're working secretly aside from PJ, against RJ. Kirkland killing Lennon was really strange and somehow proves the opposite of this theory about him, but we'll find out in season 6 about that.

Bret Stiles and Brett Partridge are the key for the RJ mistery.

PJ knows much more about RJ then he shows. Think he's already done something twisted and tricky (the toothpick, Lorelei Martins being dead, the CD, the list, ...) who knows.