I think there is a good possibility that killers are born as well. I was reading a story yesterday about a couple whose kid is extremely violent, is obsessed with knives, bleeding and stabbing..Here you can read it.
Years ago the wife and I had a Foster Daughter with Reactive Attachment Disorder (RAD)
These children can not form normal bonds or relationships. It is often found in children that lived in orphanages, particularly from the Soviet Union. When the facilities are overcrowded they are unable to give the children the attention they require.
The children have no one to soothe them and they learn to "live" with out affection.
That was on Dr. Phil yesterday. He thought the parents were overreacting to the boy.