Tonight the BBC will explore the mind of a killer in "The Mystery of Murder: A Horizon Guide." The documentary is hosted by British journalist Michael Mosley and will explore if the violent crimes of murderers are a result of their physical makeup or upbringing. Science, though, suggests both theories may hold some truth.

The Murder Gene

In 2009, researchers from Brown University linked “the warrior gene,” a genetic sequence found in around 30 percent of the male population, to an increased susceptibility to aggressive behavior. The warrior gene, also known as MAOA, regulates neurotransmitters involved with impulse control. In the study, the researchers found that individuals who possessed this gene exhibited more aggression in response to lab-created provocations.

Although this gene is also found in many convicted violent criminals, it is also found in perfectly functioning members of society. This led the scientists to conclude that simply posssessing MAOA wasn’t enough to drive a person to kill.

Murder On The Mind

The brain of murderers has been a popular topic for scientists for centuries, but the most in-depth and contemporary research on the subject is that of Dr. Adrian Raine, now at the University of Pennsylvania. Since the late 1980s, Raine has been analyzing the brains of vicious criminals looking at telltale signs of a killer. As reported by The Guardian, in 1994 Raine conducted a PET scan of 41 convicted killers and paired them with a “normal” control group. The study found major differences in the prefrontal cortex of murderers, the area of the brain associated with controlling impulses. As reported by the BBC, in later research Raine also found that criminal brains often had an overactive amygdala, a region responsible for creating emotions.

A similar study was later done, only this time looking at the brains of psychopaths. Psychopaths are described as individuals who are indifferent to the emotions of others, and often this lack of empathy will lead them to commit violent and heinous crimes. Researchers from King's College London Institute of Psychiatry found that brains of psychopaths differed from both the brains of “normal” individuals and the brains of other non-psychopathic violent criminals.

While the cranial differences in the criminal were plainly seen, explaining how they become to be that way was more difficult. Raine suggested that early life abuse could cause such changes in the brain’s structure, with the prefrontal cortex being especially vulnerable during early childhood. However, as reported by the BBC, a history of abuse is only found in a small percentage of convicted murderers, making this correlation inaccurate.

Nature vs. Nurture

It may seem that the recipe for a murderous nature is a combination of both genetic predisposing and environmental cues. But although some of us are “wired” differently than others, ultimately biological makeup is not a destiny for crime.

"If you've the high-risk form of the gene and you were abused early on in life, your chances of a life of crime are much higher. If you have the high-risk gene but you weren't abused, then there really wasn't much risk," Jim Fallon, professor of psychiatry at the University of California, told BBC.

According to Mosley, it’s estimated that every hour of every day at least 50 people are murdered somewhere in the world. The crime is borderline an epidemic, although one that has plagued the human race since the beginning of time. The researchers ultimately hope to crack the code of what drives a person to kill in order to perhaps prevent others from going down this path.