Abram de Swaan spent his first years of life in the Netherlands, witnessing the horrors of World War II. After dedicating decades to the study of human behavior, the award-winning sociologist was so struck by the 1994 Rwandan genocide’s eerie resemblance to the systematic killings of the Holocaust that he decided to investigate the roots of mass murder. De Swaan’s new book, The Killing Compartments: The Mentality of Mass Murder, peers deeply into the minds of those who carry out atrocities, seeking to understand the societal and psychological conditions that give rise to mass murder.

From the destruction of the indigenous societies of South America by the Spanish to the horrific human-rights abuses of the current North Korean government, de Swaan shows that while every atrocity is different, both mass killings and those who commit them have certain commonalities that stretch across time and culture. 

Science of Us recently spoke with de Swaan about his book and his research. 

Which factors make an individual more likely to be capable of committing mass murder?
It’s like a probability distribution. Let me tentatively say that in at least three respects, perpetrators tend to be somewhat different from most people. Almost all mass perpetrators I know of think it's very important to obey their commanders and to be loyal to their comrades. And surprisingly, they're devoted family people. So they do have a conscience. But it's a very restricted conscience, and anybody who is beyond that immediate circle doesn’t matter.

Secondly, generally, in the accounts of perpetrators you find very little overt, as the Americans call it, agency. A sense that you are an actor in your own life, and that your life is in part the consequences of what you decided to do. To them, life just occurs, it just happens to them. A famous Dutch man of letters once said about the SS, “They once and for all decided not to decide.”

The third thing, which is the most striking, is that these are people who feel no empathy and have no sympathy for anybody outside of their immediate circle. They don't know what pity means. Sometimes they think they know what it means, when they're in front of the judge and they say, “Oh, your honor, it was awful. I got all this blood on my uniform. And the shouting and crying of the victims was impossible to bear.” But it was impossible for them to bear, and it was their uniform.