A new FBI study of “lone offender terrorism” in the United States painted a grimly familiar picture of the people who carry out these attacks. 

The report, released Wednesday, described men with histories of physical violence and people who nursed grievances and wanted to publicize their viewpoints. Rather than erupting without warning, the attackers had worried the people around them, the study found. And in many cases, someone in the attacker’s life knew they endorsed violence to further their ideology.

“While the attackers in this report were ideologically-motivated offenders, they were rarely completely isolated and alone, and they traveled down the same observable and discernible pathways to violence as other attackers,” FBI Director Christopher A. Wray wrote in a message accompanying the report. 

The FBI study, which was released Wednesday, examined dozens of attacks over more than four decades. It is the latest in a growing body of research examining the mass attacks, typically carried out by lone individuals. 

These violent rampages — at churches, synagogues, schools, movie theaters and other public spaces — have become agonizingly familiar for Americans. Law enforcement officials have worked to reassure the public in the wake of such violence.

For the new study, the FBI looked at 52 cases from between 1972 and 2015, covering attempted or successful acts “of lethal violence in furtherance of an identified social, political, or ideological goal.” Thirty-three of the cases involved attackers killing people. Overall, 258 people were killed and nearly 1,000 injured in the attacks the FBI examined. 

The research looked at people who were “primarily radicalized in the United States,” carried out their attacks within the country and did so without direction from a terror group.

Among the primary motivations cited in the study were anti-government extremism, racial extremism “advocating for the superiority of the white race” and Islamist violence. In some cases, attackers had multiple extremist ideologies that blended together. 

But these ideologies did not exist in a vacuum, something experts have noted about other mass attackers. Instead, they blended with personal experiences and grievances.

Most of the attackers in the study had a grievance, described as a real or perceived sense of injustice or of being wronged. Many of the attackers also gravitated toward conspiracy theories, with a large number consuming “radical ideological material or propaganda.” 

Other common elements recurred in many of the cases examined in the study. The attackers were all male, mostly white and almost all born in the United States. They tended to be single and, more often than not, were not going to school or working when their attacks occurred. This last factor is significant, the authors write, allowing attackers free time to focus on both their grievances as well as plans for their attacks. 

Most of the attackers used guns. Rather than being cut off from the world, they tended to interact with other people both in person and online. Nearly all of them had authored some kind of account laying out their grievances and viewpoints, including attackers in New Zealand and El Paso.

Wray, in his letter introducing the report, said it was “unique from other research on this topic,” because the authors were able to rely on case files and law enforcement records. 

The report’s authors include two officials with the FBI’s Behavioral Analysis Unit. Wray noted that the report is not meant merely as an exercise. Instead, he writes, the authors are trying to offer suggestions for readers hoping to prevent future attacks.

Predicting attacks by lone individuals “is not possible,” the authors write. But research and experience have shown that such attacks “may be preventable through early recognition and reporting of concerning behavior.” 

Echoing previous research, the authors found that someone had expressed concern about each attacker beforehand, often about interactions they had with other people, their anger or their mood. 

Most of the attackers had been arrested at least once before their attack. More than half “were known to have previously carried out physical violence,” and even more had shown signs of explosive, aggressive behavior such as making threatening statements. 

In most cases, someone sought to address the concerning behaviors, usually by expressing their unease to the person or others in their lives. In fewer cases, people reported concerns to law enforcement. 

Mental health issues are often raised after mass shootings and other attacks. After mass killings just hours apart in El Paso and Dayton, Ohio, over the summer, President Trump blamed “mental illness and hatred,” echoing familiar rhetoric from him and many other politicians. 

Most studies have found that a fraction of mass shooters have mental health issues, pointing instead to other factors that are likelier to precede mass killings, such as senses of resentment and grievance, a desire for infamy and studying other shooters. 

This report found that about 20 of the attackers — or about four-in-10 — had formal diagnoses of at least one psychiatric disorder, including several diagnosed after their attacks. In nearly as many cases, the authors noted that people suspected the attackers had mental disorders that had not been diagnosed. Ultimately, the authors noted that research shows that a psychiatric diagnosis alone does not predict whether a person could carry out violence. 

The report comes as many across the country continue to worry about active shooter attacks and gun violence. After the report was released, Attorney General William P. Barr announced a new, nationwide program to attempt to stem gun violence.

This plan, known as Project Guardian, calls on U.S. attorneys to coordinate with their local counterparts to consider federal charges — which often come with stiffer penalties — on those arrested with guns or found to use guns in crimes.

The plan also calls on federal authorities to better share information with their local counterparts and to make sure authorities record instances in which those with mental illness are prevented from buying a firearm in a database.

Matt Zapotosky contributed to this report.