Brain damage in Serial killers

The article "This man spent 35 years studying the brains of serial killers"  reports about a TED talk by neurologist Dr Jim Fallon from the University of California Irvine, Fallon on the mind of psychopathic killers.
 
He found three common elements of serial killers:
 - All of the psychopaths that Fallon studied has damage to their orbitofrontal cortex (above the eyes) and to the interior part of the temporal cortex. In addition, all of them had some other of brain damage in a variety of combinations.
 - Possession of the high risk violence gene, the MAOA is also common to psychopathic killers. The gene MOAO is sex linked, and exists in the X chromosome. This gene causes overproduction of serotonin what causes insensitivity to it. As such, the control of anger and stress relief is impotent in later life.

 - The deciding factor is exposure to extreme violence at a young age