I wanted to know more about Cleve's past

Nice film, James Woods did a good job as the edgy, psychopathic hitman. But I noticed one thing that the writer-policeman said to Cleve, the hitman: "People want to know your family, they want to know where you come from." Actually, the film viewers would have liked to know the same thing. How did he become such a psychopath? Especially, given his parents were such decent people. I think the movie should have elaborated on that a bit more.