It's called Monoamine oxidase A or shorter MAO-A or more popular, the "warrior gene". However, that is in public misunderstood (Jerry Bruckheimer's shows did a lot of work to promote the misunderstanding). Technically, there are a number of variants of this genom and in Caucasians are two of the most common. The studies, at first limited to Caucasians, seemed to indicate, that some other variants result in some kind of preposition for becoming an SK. In the meantime, they found out, that other ethnic groups have other variants revalent and thus, now everything goes slow because nobody wants to be the one saying by accident, that maybe people with a certain skin color have a higher probability. And in fact, this would be bull anyway. A lot of the trouble comes from the way. specialized scientists work today:
The neurobiologist: x% of all serial killers have one of those genetic variants. That is more than my testgroup for the normal population (which originally was all white). THe neurobiologist wouldn't touch a book about social psychology to save his life.
The socialpsychologist: Has no idea what MAO-A technically is. For him, it could be a little green man with fishtail. And he wouldn't touch a book about genetics to save his life. But he knows, that certain social environments (for example abusive parental households) breed more SKs. So he counts out the rare cases in which the SK comes from a nice middle class family just out of his study as exception from the rule.
The mathematician: Scratches his head. How does the neurobiologist make a sample size statistically relevant if the sample is lesss than 0,001 promille of the population and the targeted group makes anyway statistically less than 0.01 promille of the population. Because the mathematician knows, this is mathematically impossible and therefore rubbish, but he wouldn't go down the rabbit hole and talk to a psychologist unless he is just at the right time going through a bad divorce.
And so it goes on and on. Everyone makes his studies about exactly one aspect, nobody looks for the whole picture. And all refuse to talk to each other.
But in fact, things are pretty simple: Certain variants of MAO-A flood the brain during the development with large amounts of serotonin (other substances as well, but the key seems to be serotonin). So, at early age, the result is some kind of immunity to serotonin and it's calming effects (S. is also called the happiness hormone, because it calm's down and gives some kind of happy relaxation, but makes also emotional).
Now, less impact of serotonin makes people less emotional, distanced and in consequence sometimes socially a bit awkward because they tend to be logic in a twisted way when everybody expects them to be emotional. It could be a thing, that makes killing easier - or other activities which are normally emotionally hard - but it doesn't make one a killer. Someone with the warrior gene has a lot of career choices: Politician, business management, cop, artist (especially known in writers and actors), gardeners (lone job not so much bothering with other people), trucker, ... and so on, the list is too long. So what we really talk here is just raising the chances to become a successful killer.
