I read a book called Soul by Tobsha Learner about the search for a genetic trait that allows some people to kill and feel no remorse. It's like 2 books in 1, half the book is about Lavinia Huntington a 20-year-old girl in England in the 1860's, and the other is about her great-great-great granddaughter of Lavinia, Julia Huntington. Julia is a genetisist working for the US Defense Department trying to find the genetic trait mentioned above.
Lavinia is accused of murdering her husband and executed. Julia killed a man while working in Afghanistan but only told a couple people, she feels no remorse for killing the man-it was an automatic response.
"Soul is the story of two women, across two eras, and their struggle with obsessive love and revenge. Part murder mystery, part psychological thriller, part commentary on genetics and human behaviour, sexual jealousy and betrayal, it is both provocative and unputdownable."
http://privateramblings.blogspot.com/2007/04/soul-tobsha-learner.html
The fact that someone can kill another person without any remorse is somewhat disturbing but believable. The search for the genetic trait that allows people to do murder with no remorse is not a wasted search. People are born everyday with genetic problems, this problem is probably just one of those rare birth defects that a person doesn't have that sense of reasoning and feeling in their brain.