It can't be Quinton, the producers have said that it's a prominant character from all 3 seasons, he was just introduced this season.
I think it's Liz, she has access the the drug the carver is using to parallize(sp?) her victims, she has access to Christians dna (remember in one episode she asked him to help her get pregnant and he obliged?) she totally flipped out when the girl faked a carver attack and didn't put her all the way under when she went in for surgery, and even though she's female she can still violate her victims with inanimate objects just my opinion. I can't wait until Tues, the suspense is killing me.