One thing that I noticed was the trident symbol. It was tattooed on Antony Longmoore's arm, it was used on his computer to find the last hanging location,
AND, it was used by the Cain killer as well, on the wheel Erica had to open the door with. So, we can assume that Davies killer and Cain is the same person.
Now...suspects...
I think I'll place my bets on Cordelia for now. She was at the cemetery the night Scott died. Aaand, she mentioned that she took care of the "family business", and that her dead brother Max was an ace at it. Hmmm...

So Max died in a fire, and Cordelia picked up where he left of.
What's that? She said Max died six years ago? That's in crazy-time, silly! It goes twice as fast as regular time!