That one hits you different (pun intended) because it's someone close to you and you would never see it coming. Finding out more about his past would presumably move him up in the list for me too though. Jason as mentioned is another - there are a few in Hillside actually. I think they are above Ethan (so far) because it's more organised, whereas Ethan feels small-time.
Jason and his group are probably where Ethan will end up if he can carry on getting away with things - part of a group trafficking hopeful models and actresses and drugging them up to be passed around on billionaires' yachts, then killing them off when they have served their purpose or if they start to resist too much. I see a lot of parallels here actually, if Ethan is seen to be at the start of that sort of journey... Putting your childhood friend through that though, that's another step on the evil staircase...