Right now I think it is Carroll or Raleigh Woods, but that'll change, probably several times.
I thought it might be helpful to keep some notes, start our own murder file and see if our combined intelligence can outsmart the creators.
Carroll might be a little too easy - guy goes to investigate serial killer town and goes mad -- but it can't be written off. He is unaccounted for and would have no problem killing locals (unlike Warren)
Raleigh is the only one I can think of with motivation. I know serial killers aren't typically motivated like regular killers, but he could profit quite a bit if there was another killer, especially if he wanted to bring some Killer Con there. I could even speculate further that through some weird science (bees, anyone) inspired / created the other butchers to (a) be the best serial killer of them all, wielding people like weapons, or ( to offset the stigma of being the grandson of a serial killer - seems pretty thin, but it's the best I got right now.