I'll go with the DeMeo crew. From what I can remember, it seems most if not all of their murders were in furtherance of a criminal enterprise as opposed to serial killers which in my view is more like a thrill killing. I know that one specifically, the one involving the body shop owner (Can't recall his name) was partially in retaliation for shooting Chris Rosenberg in the face but wasn't it also to prevent him from informing on the DeMeoo crew??? Also I can't rule out Pitaro