PARIS - Adam Lanza, killer of 20 children and seven adults, including his mother, is a mass murderer – he murdered a large number of people in a short time in one place. He then committed suicide in a classroom.

Ending your life or having the police shoot you dead is often part of the mass murderer’s plan – as opposed to the serial killer who usually tries to escape the police and kills repeatedly, not in a single strike.

Mass murderers are not, according to statistics, mentally ill in the psychiatric sense. That is to say they are not living outside reality. Serious mental illnesses such as schizophrenia are the source of disordered behaviors. Whereas a mass shooting requires organization, preparation, being able to acquire and make proper use of a gun as well as defining a strategy to gain access to the site.

The reason why they are commonly labeled as insane is because they are not perceived as normal people, given their personality and character disorders. Actually, statistically mass murderers possess some common characteristics.

The most common characteristics are social isolation, introversion, withdrawal and a relative deficit in social skills and relationships. At the same time, signs of paranoia can also be observed. These people often believe that people are after them, bullying them or ignoring them.

These features of course do not make someone a murderer. For a person to commit an act as extreme as mass murder, these characteristics have to be very intense. On top of the paranoid behavior, there is also megalomania and self-centeredness.

Personality disorder v. mental illness

When mass murderers leave written texts, we often find feelings of aggressiveness, vengeance, a will to stand out, to show the world they exist. Taking multiple lives is an aggressive way to leave a mark that says, "Look at who I am." In their destructive rampage, they unleash a murderous violence on others, which is also quite desperate, since suicide is part of their plan.

There are two criminology aspects that set the Newtown massacre apart. First, the victims are very young children – six to seven years old – whereas most of the shootings following Columbine took place in middle schools, high schools or colleges. Also, the killer started his rampage by killing his mother, while in most cases, the mass murderer leaves his family unharmed.

The murderer’s brother apparently claimed that Adam Lanza suffered from a certain kind of autism. This is a clinically interesting element since this specific illness could explain these two criminology aspects. It should however be said that most mentally ill patients and autistic people, even the ones afflicted with Asperger syndrome, are not violent.

Mental pathologies do not in themselves lead to the aggressive behaviors behind mass killings. These events are usually born from insanity of the human mind, personality and character disorders rather than mental illness.

*The author is a psychiatrist and a criminologist