PHOTOGRAPH BY ADRIAN WYLD/THE CANADIAN PRESS/AP

When Corporal Nathan Cirillo stood guard on Wednesday morning at the National War Memorial in Ottawa, which stands kitty-corner from Canada’s Parliament, he carried a rifle that was unloaded. Although the sentries at the monument are real soldiers, their presence is more about preserving the dignity of the monument than defending against violent attacks. The position of memorial guard was created after a 2006 episode in which three hooligans urinated on the tomb commemorating the war dead.

As an unarmed soldier carrying out a civic responsibility, Cirillo, who was in his mid-twenties, existed in a kind of liminal state between military and civilian status when he was shot early in the day, by Michael Zehaf-Bibeau, a thirty-two-year-old Canadian-born convert to Islam. Zehaf-Bibeau then tried to storm Canada’s Parliament, where he was killed during an exchange of fire inside the building, by the parliamentary sergeant at arms, Kevin Vickers. In a sombre speech that night, Canadian Prime Minister Stephen Harper described Zehaf-Bibeau as a “terrorist” and linked his acts to an “ISIL-inspired” attack two days earlier in Saint-Jean-sur-Richelieu, Quebec, in which two Canadian soldiers were hit by a car driven by Martin Couture-Rouleau, a twenty-five-year-old who was also a convert to Islam. One of the soldiers, Warrant Officer Patrice Vincent, died from his injuries.

Implicit in Harper’s comments was a link between these killings and Canada’s participation in the war against the Islamic State in Iraq and al-Sham (ISIS). He wasn’t the only one to see the events as connected to Canada’s foreign policy. The American investigative journalist and civil libertarian Glenn Greenwald, who is travelling in Canada this week on a lecture tour, made the same connection in a post for The Intercept. The article was published the same morning that Corporal Cirillo was killed, but written before the murder.

Greenwald contested the idea that the killing in Saint-Jean-sur-Richelieu was an act of terrorism, per se. Rather, he claimed, it was the natural byproduct of the West’s interference in the Middle East. “It is always stunning when a country that has brought violence and military force to numerous countries acts shocked and bewildered when someone brings a tiny fraction of that violence back to that country,” he wrote. “Regardless of one’s views on the justifiability of Canada’s lengthy military actions, it’s not the slightest bit surprising or difficult to understand why people who identify with those on the other end of Canadian bombs and bullets would decide to attack the military responsible for that violence. … The issue here is not justification (very few people would view attacks on soldiers in a shopping mall parking lot to be justified). The issue is causation.”

This word, “causation,” is a strong one. Greenwald sees the causal relationship as this: “The statements of those accused by the west of terrorism, and even the Pentagon’s own commissioned research, have made conclusively clear what motivates these acts: namely, anger over the violence, abuse and interference by Western countries in that part of the world, with the world’s Muslims overwhelmingly the targets and victims.”

Canada’s participation in wars in the Middle East is undeniably connected to these terrorist acts—we know that both men were inspired by events abroad. But Harper and Greenwald are wrong to frame them in such a simple, monocausal way. If military and political interference is such a dominant driving force in terrorism, why aren’t these kinds of attacks more common? Out of the more than one million Canadian Muslims, only a handful have committed terrorist acts, and fewer than a hundred people are being actively monitored by Canadian authorities as likely to join in terrorist activities abroad. Something more is obviously often at work.

Rather than hastily framing attacks in the context of a battle between the West and the Muslim world, it may be more productive, in terms of diagnosis and prevention, to look at more profiles of self-styled ISIS fellow-travelers who commit attacks as individuals. What we know of Zehaf-Bibeau’s biography offers some instructive clues. According to reports published in the Globe and Mail and elsewhere, he had a history of mental illness and of run-ins with the law, involving drug possession, theft, and making threats. He battled an addiction to crack cocaine and, in the weeks leading up to the attack, he was living in a homeless shelter. Dave Bathurst, a friend of Zehaf-Bibeau and himself a Muslim, told the Globe, “We were having a conversation in a kitchen, and I don’t know how he worded it: He said the devil is after him.” Bathurst said his friend often spoke of the presence of shaytan—the Arabic term for devils and demons. “I think he must have been mentally ill.”

According to Dr. Thomas Hegghammer, the director of terrorism research at the Norwegian Defence Research Establishment, Zehaf-Bibeau fits a profile of “converts with a history of delinquency among the Westerners in ISIL. He’s a little older than average; otherwise, there is nothing unusual about his profile.” Conversion to Islam itself isn’t a cause of violence, as we well know—Dave Bathurst, for instance, is an apparently peaceful citizen, disturbed by his late friend’s act of mayhem. What seems to be the problem, rather, is the fusion of radical jihadist ideology with other personal problems, whether they be alienation, anomie, or various shades of mental illness. In a world where “clash of civilizations” rhetoric is pervasive, it is possible that radical Islam offers the same appeal to some unstable individuals that anarchism had for Leon Czolgosz, who killed President William McKinley in 1901, and that Marxism had for Lee Harvey Oswald. If you are alienated from the existing social order, the possibility of joining, even as a “lone wolf” killer, any larger social movement that promises to overturn that society may be attractive. For a person radicalized in this manner, the fantasy of political violence is a chance to gain agency, make history, and be part of something larger.

“Islamic-extremist online recruiters are very good at pulling in people who are mentally vulnerable,” Heather Hurlburt, of the Washington-based think tank New America, said. She suggests that an effective response to the problem will draw at least as much on the insights of mental health as on the intrusions of the security state. The constant balance that needs to be struck, she said, is between monitoring dangers without alienating allies in the community, as happened with New York City Police Department’s polarizing surveillance of mosques. As Hurlburt noted, “Some of the efforts, such as surveillance of college students’ social-media accounts and police informers in mosques, have been controversial and counterproductive. Insights from mental health, especially post-Columbine, tend to focus on more community-centered efforts, which may give family and clergy tools and non-stigmatizing places to turn for help. Tragically, the father of the Canadian who killed a Canadian soldier with his car on Monday had previously reported him to the authorities.”

Recruiting troubled individuals who can be pushed toward violence ties in well with ISIS’s larger strategy. As Hurlburt observed, ISIS “seems to calculate—correctly, in my view—that small-scale lone-wolf attacks on symbolic targets will get it outsized attention. So you see these propaganda broadcasts encouraging individuals who may be mentally unstable, who may have had little or no actual training, to use weapons like knives and cars that will surely lead to the attackers' capture or death. The propagandists seem to understand the link between certain forms of mental illness and susceptibility to mass violence, even if we don't.”