Knowing dexter season endings suck, and someone always die...
My guess is the Psychiatrist is the brain killer dude. She's like Dr. Jekyll and Hyde.
Hanna is gonna get killed by the private investigator soon by mistake, and Dexter is gonna die last episode while killing the Psychiatrist, and morgan is gonna see it, and dexter is gonna die in her arms.
Quinn is probably the guy beating up the women, doesn't really fit in though, but would match trying to get Zach to jail.
what are your guesses?