I Am Not a Serial Killer is a thriller with fantasy/horror aspects. It may count as YA, but I'm honestly not sure about that.
Review:
John Wayne Cleaver thinks it's his fate to become a serial killer, and he's doing what he can to try to avoid it. He's attending his therapy sessions with Dr. Neblin, and he's made up all kinds of rules for himself, based on commonly recognized indicators that someone might become a serial killer. No paying too much attention to one particular person, no hurting animals (in fact, as little contact with animals as possible), etc.
He enjoys helping his mom and aunt out at their mortuary. The bodies and embalming process fascinate him, and he likes the quiet. However, something new going on in town has snagged his attention: murders that he thinks are the work of a real serial killer. As he looks into the deaths as much as possible without technically breaking his rules, he starts to believe that he's the only person in town who stands any chance of stopping the killer.
