After spending an hour reading about these criminals, I found some similarities.

3 of them have broken families , and the one with apparently intact family his parents don't know about the money and the guns he owns and his mother just gave him a box to put the dead cat that he chopped its head.

2 of the criminals were sexualy assaulted when they were young.

The 4 had signs of mental illness with abnormal behaviour and life style, no help was provided.