WHY SOME OF US ARE MURDERERS

This BBC Documentary is a must see for anyone who includes murderous characters in their books or who has those enticing inclinations. 

In a nutshell, many/most murderers have a mixture of 'the warrior' gene, (30% of the population); were abused and unloved as children or suffered damage to their brains, through head trauma.
This fits the idea that we succeed or fail, murder or not as a result of scientific determinism or luck. Free will either does not exist at all or allows only minimal manoevre within our predetermined destiny.

https://www.bbc.co.uk/programmes/b0555v7v