There’s a perception that all serial killers must be crazy, or at least “born that way,” and a few serial killers (Son of Sam, for example) actually were paranoid schizophrenics who heard voices telling them to kill. Most, however, are sane, or suffer from “personality disorders” – a very fuzzy diagnostic category which may or may not take away choice.
Some people are afraid of the mentally ill, and this is absolutely uncalled for. Only a very tiny percentage of mentally ill people are dangerous, and the odds of you’re meeting one are almost non-existent.
My point is that looking for causes and if there’s bechirah is not useful. The person has to be kept from harming others, and the fact that they’ve killed more than once makes them assumed to be dangerous – a shor mu’ad, so to speak.