Nearly a quarter of mass shooters used illegal firearms, Secret Service report finds

Nearly a quarter of mass shooters from 2016 through 2020 used an illegal firearm and most assailants exhibited concerning behaviors before their attacks, according to a report published Wednesday by the Secret Service's National Threat Assessment Center. 

The study analyzed 173 public attacks in which three or more individuals were injured or killed. A total of 180 attackers were identified, 168 of which were lone perpetrators. The attacks resulted in a total of 513 deaths and 1,234 injuries. 

Most of the attacks, 73%, involved firearms, and 23% of the incidents involved at least one gun that was illegally owned, the report states.

In more than two-thirds of the attacks, 68%, the aggressors "directed harm toward random persons," and in some cases targeted individuals based on gender, religion or ethnicity. The remaining 32% of attackers had specific targets, largely motivated by personal issues. 

In total, over half of all attacks, 51%, were motivated by personal, domestic or workplace grievances, while 18% were motivated by bias or ideological or political beliefs.

Additionally, most of the perpetrators, 58%, had some form of mental health history, whether it was depression, suicidal thoughts or psychotic issues.

"We encourage our public safety partners to review the information within this report and apply it to their own practices for providing a safe environment in communities across the country," threat center Director Kimberly Cheatle said.