If you've ever murdered someone, I bet this question has crossed your mind.
Why do we have a separate category for murderers called the "cold-blooded killer"?
Is there really any other kind? You can be named a cold-blooded killer or you can kill someone in a cold-blooded fashion. This revolves around the level of enjoyment with which you kill. If you are downright gleeful after a murder spree, attend and enjoy a baby shower later that day, and have an awesome sleep with your favourite stuffed animal that night, you are cold-blooded.
If you murder someone and find it's not quite your bailiwick; if you get a little down afterwards and cancel your pilates class; perhaps a little spittle comes up from feeling sick about it, that's entirely normal, for you. You are not cold-blooded.
You are…a lukewarm-blooded killer?
The lukewarm-blooded killer strikes again. He doesn't really enjoy killing. He's rather lukewarm about the whole thing. It's just that he's so good at it.
He never brags about his work. Never mentions his murder stats, even though if he were in sales with those numbers, he'd get the set of steak knives every time. In fact, he prefers volunteers to hunting down unsuspecting victims. It's kinder.
After a typical murder, he'll toss and turn in bed for a week, racked with guilt. Doesn't take any trophies. He'd rather just beat people up, but he's not good at boxing.
Read the book. In Lukewarm Blood.