I am working on a dark urban fantasy novel involving a set of mage characters as the protag group. One of them has no problem with killing anyone who threatens him and his friends, and has almost no bad reaction to seeing corpses of people he doesn't know. He still cares about his friends, and has his morality like anyone else. He is not like Dexter Morgan. My character feels normal people emotions. The only difference from him and a normal person is he has no second thoughts or remorse about killing the bad guy, and on some occasions does so with great pleasure. Also, his main method of killing is to buff his own strength with magic and beat people to death, so you have an idea of how grisly his kills are. His back story is a little sad, but not outright tragic. He recalls no memories from before age 15. Doesn't know any family of his own. Him and his friends got abused by some of the staff in the orphan house. There are opportunities to explain a character that is a total sociopath with that back story, but this character retains some of his humanity. I am just wondering if I would leave too many hole with this kind of character with this back story and no further explanation.