LONDON -- From a comfortable couch in his London living room, Sean O'Callaghan had been watching the shaky televised images of terrified people running from militants in an upscale mall in Kenya. Some of those inside had been asked their religion. Muslims were spared, non-Muslims executed.
"God, this is one tough lot of jihadis," said a friend, a fellow Irishman, shaking his head.
"But we used to do the same thing," Mr. O'Callaghan replied.
There was the 1976 Kingsmill massacre. Catholic gunmen stopped a van with 12 workmen in County Armagh, Northern Ireland, freed the one Catholic among them and lined up the 11 Protestants and shot them one by one.
Mr. O'Callaghan, a former paramilitary with the Irish Republican Army, has particular insight into such coldblooded killing.
On a sunny August day in 1974, he walked into a bar in Omagh, Northern Ireland, drew a short-barreled pistol and shot a man bent over the racing pages at the end of the counter, a man he had been told was a notorious traitor to the Irish Catholic cause.
Historical parallels are inevitably flawed. But a recent flurry of horrific bloodletting -- the attack in Nairobi that left 60 dead, the execution by Syrian jihadis of bound and blindfolded prisoners, an Egyptian soldier peering through his rifle sight and firing on the teenage daughter of a Muslim Brotherhood leader -- raises a question as old as Cain and Abel: Do we all have it in us?
Many experts think we do. For Mr. O'Callaghan, it was a matter of focus.
"What you're seeing in that moment," he said in an interview last week, "is not a human being."
It is dangerous to assume that it takes a monster to commit a monstrosity, said Herbert Kelman, professor emeritus of social ethics at Harvard.
"We are all capable of such things," said Mr. Kelman, 86, whose family fled Vienna under the Nazis in 1939. "It doesn't excuse anything, it doesn't justify anything and it is by no means a full explanation. But it's something that is worth remembering: We are dealing in a sense with human behavior responding to certain circumstances."
Overcoming a deep-seated proscription against killing is not easy. In his book "Ordinary Men," Christopher R. Browning described how a German police battalion staffed with fathers, businessmen and plumbers struggled as they executed thousands of Jews in Poland. How many among them missed at point-blank range. How they vomited and cried in the forest after massacring mothers and their children. How hard they had to work at becoming killers.
A culture of authority and obedience that supplants individual moral responsibility with loyalty to a larger mission helps loosen the moral inhibition against murder, social psychologists say. So does a routinization of violence, as well as injustice or economic hardship that allows the killer to see himself as the true victim.
But perhaps the most important ingredient is the dehumanization of the victims, said David Livingstone Smith, professor of philosophy at the University of New England and author of "Less Than Human: Why We Demean, Enslave, and Exterminate Others."
"Thinking about your enemies in subhuman categories is a way of creating a mental distance, of excluding them from the human family," he said. "It makes murder not just permissive but obligatory. We should kill vermin or predators."
The Hutus in Rwanda called the Tutsis cockroaches, the Nazis depicted the Jews as rats. Japanese invaders referred to their Chinese victims during the Nanjing massacre as "chancorro," or "subhuman." American soldiers fought barbarian "Huns" in World War I and godless "gooks" in Vietnam.
In Northern Ireland, "taig" was a popular slur for Catholics. Where Mr. O'Callaghan grew up in Tralee, County Kerry, they called Protestants "sassanagh," Gaelic for "foreigner."
Later, after The Troubles had started in 1968 and images of Catholics being bombed out of their houses in Belfast flooded the news, creating an army of angry young Catholic men, Protestants, too, became "Huns."
Such labels help, said John Horgan, director of the Center for Terrorism and Security Studies at the University of Massachusetts, Lowell, and author of "Walking Away From Terrorism," a book on experiences of former militants. Still, he said, "They wrestle with their conscience. They don't sleep well at night." It is no coincidence, he said, that terrorist executions often involve hooding the victim or slitting the throat from behind. "Watching the face when you kill someone is a very difficult thing to do," he said.
Mr. O'Callaghan never dared look into the face of the man he killed that day in 1974. When he closes his eyes and searches for it, all that comes back is a grainy photograph from the next day's newspaper.
He had joined the Irish Republican Army at 15. A country boy seething at the injustice he saw in the Belfast refugees streaming into his southern Ireland county, he became an explosives and firearms instructor, training young men in mountain camps near his home. "We felt that we were part of something," he said.
The older men taught the younger ones about the 1916 uprising, an event elevated to a near-mystical status because it fell on Easter Monday. He fell hard for the Irish republicans' emotional blend of Catholic religion and Irish nationalism.
A six-month jail term after he was caught with explosives only made him angrier. In May 1974, he was sent to Northern Ireland and took part in bombings and robberies. One night he got a call from Harry White, a Welshman who worked for the I.R.A., with a tip that Peter Flanagan, legendary in the I.R.A. as a Catholic turncoat and "torture chief" for the Royal Ulster Constabulary, often ate lunch at the Broderick bar. "He drives a blue Volkswagen," Mr. White told Mr. O'Callaghan, and said to look for the car outside the bar.
Mr. O'Callaghan was 19. He found his quarry, and trained his eyes and his gun on a faceless torso in a blue shirt. The newspaper dropped to the floor. The torso followed, a blue mass rolling off the bar stool in slow motion. A voice pleaded, "Don't."
He recalled what his grandmother had told him when he was only 9: "When you shoot a British policeman, dig him up and shoot him again because you can never trust them."
He fired eight times. It took perhaps 10 or 15 seconds.
Years later he learned that Peter Flanagan was not the monster that the I.R.A. had made him out to be. Mr. Flanagan had been unarmed, had testified against British police officers at the European Court of Human Rights in Strasbourg, and had probably never tortured a soul.
Mr. O'Callaghan eventually became an informer for the Irish police and later turned himself in, pleading guilty to 42 crimes including this one, a journey he partly chronicled in a memoir called "The Informer." He was sentenced to 539 years in prison. After eight years he was pardoned, and in 1996 he walked free. He turned down an offer for witness protection -- to take responsibility and to make peace. "But of course you never really do," he said.
He had killed many times, ambushing shadows in the dark on army barracks, firing a mortar, but never like this, up close. The torso still comes back to him, in dreams and sometimes in the middle of the day.
But what haunts him most was a comment his driver made that day. She was a Belfast woman with a worn face who went by the nom de guerre Lulu. On the way to the bar, she had been so nervous she drove the wrong way up a one-way street and had gotten them lost.
Later, after they sped off, dumped the stolen car, and made it to a safe house, Lulu finally caught her breath.
"I feel sorry for his mother," she said.world
This article originally appeared in The New York Times. First Published October 13, 2013 2:01 PM