https://www.ted.com/talks/jim_fallon_exploring_the_mind_of_a_killer
in this speech by Jim Fallon about the making of a murder he goes in to neurology side about how the The different brands of some of the most notorious murders are the same, now as everyone is different and the different brains have more stress on the specific parts they tend to create a personality that is more aggressive due to high amounts of serotonin in the brain now Jim Fallon said that these high serotonin spikes often comes from a traumatic experiences or being passed down from generation to generation. In the novel In Cold Blood by Truman Capote both of the killers have had a very Trumatic experience with their family and how they grew up. One of them has had a very Trumatic experience with their father not being very supportive of their wishes to pursue life how they would like to. Also one of their siblings has passed away which will also cause a very big Trumatic experience in the persons brain causing high spikes in serotonin.