Serial killers born or made

The question "Are serial killers born or made?" inevitably comes up in almost any discussion of the most notorious and most barbaric serial killers in human history (that is, serial killers who not only satisfy the FBI’s definition of a serial killer but who instinctively make us think of them as sadistic monsters—the killers who, in Emily Dickinson’s words, trespass the forbidden boundary between fiction/fantasy and reality.).*

Not unsurprisingly, no one really knows the answer to this question.

The most likely answer, though, is that the majority of the most prolific and dangerous serial killers were genetically disposed to behave anti-socially and furthermore grew up in an environment that cultivated a disregard for the lives of others.

*[According to the FBI, in order for a killer to be a serial killer he or she must commit at least 3 murders over a time period of at least 3 years at 3 different locations with an emotional cooling off period in