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The Secret Service analyzed 173 mass casualty attacks. Here's what they found.

Secret Service analyzes mass casualty attacks
Secret Service report analyzes trends in mass casualty attacks in the U.S. 07:55

Nearly three-quarters of assailants used guns to carry out mass-casualty attacks between 2016 and 2020, according to a study released by the federal government Wednesday. 

Over one-third of the attackers experienced unstable housing within two decades of their attack. And nearly one-quarter shared "final communications" in the run-up to launching them, including calling people to say goodbye, authoring suicide notes and posting writings online.

The 72-page report, authored by the U.S. Secret Service's National Threat Assessment Center, analyzed 173 incidents that resulted in three or more individuals injured or killed across public or semi-public spaces, including businesses, schools and houses of worship. Researchers hope new insights into the behaviors of attackers will prevent future tragedies by informing bystander reporting.  

The findings — which span 37 states and Washington, D.C. — come as a community in Monterey Park, California, mourns the death of 11 people after a gunman opened fire in a ballroom during Lunar New Year celebrations over the weekend. Less than two days later, seven people were killed in a mass shooting at two mushroom farms in the Northern California city of Half Moon Bay. Three people were fatally shot in an attack at a convenience store in Yakima, Washington, on Tuesday.

People hold a candlelight vigil to pay tribute to the victims of a mass shooting in Monterey Park, California, on Jan. 24, 2023. Eleven people were killed in the shooting.  FREDERIC J. BROWN/AFP/Getty Images

"There is no community that is immune from this," said Dr. Lina Alathari, chief of the U.S. Secret Service National Threat Assessment Center. "But we do see commonalities that will help us with prevention."

Here are the key takeaways:

1. Nearly three-quarters of attacks carried out using firearms.

Attackers in 73% of mass casualty incidents used one or more firearms to kill or maim victims.

"In terms of fatalities when you compare weapon types, over 80% of the incidents using firearms were fatal. For other weapons, just under half of [the incidents] caused fatalities," Alathari said.

Approximately three-quarters of attackers used a handgun, while roughly one-third wielded a long gun.

In one striking example, the report cites a 38-year-old Kansas man who killed three people and injured 14 others in a 2016 shooting while under the influence of methamphetamine. The gunman, who was ultimately shot and killed by police, first opened fire at a series of cars after he was sent a civil protection order from his ex-girlfriend. Roughly six months before the incident, the attacker acquired the pistol and rifle used in his attack from a different ex-girlfriend, who purchased the weapons for him after he threatened her with violence.

Nearly one-quarter of attacks involved at least one firearm acquired illegally by the attacker, including those bought through straw purchases, theft, private sellers and online parts.

Researchers were only able to track down the timing of gun acquisitions in the case of 50 attacks. But in 19 of those incidents, the firearm was acquired within one month of the attack. In the case of three, it was acquired on the same day as the attack.

2. Saying goodbye: Nearly a quarter of attackers shared "final communications."

Nearly a third of the 180 attackers — 28% — issued final communications or acts suggesting an imminent attack, including production of farewell videos, journals or writings that detailed their plans and motives. Others made goodbye calls to friends and family, left suicide notes or wrote cryptic messages to others indicating they would not see them again.

"Final acts, some of which were part of planning, included attackers terminating a lease, giving away personal possessions, no longer buying food for a pet, verifying or changing life insurance, and securing finances for family members," according to the report. 

Prior to detonating an explosive inside his RV on Christmas Day, 63-year-old Anthony Quinn Warner, who took his own life and wounded three others in downtown Nashville, gifted his house and told a client that he was retiring. Days before the bombing, he gave his car to a friend. Just hours before the attack, he broadcast announcements from his RV warning nearby pedestrians of an imminent explosion and ultimately counting down.

In 33 of the attacks, assailants made statements or engaged in prior behaviors that indicated they did not plan to survive the attack. Of those, 18 attackers died by suicide, including two who counted their shots, saving the final bullets for themselves.

3. Nearly all attackers experienced one or more significant stressors within five years of the attack.

Roughly 93% of attackers dealt with personal issues ranging from health problems to divorce, domestic abuse, car accidents, school expulsions, disciplinary actions at work and cyber bullying, among a slew of other challenges.

For 139 attackers — 77% — the stressors occurred within one year of the mass-casualty incident. Seventy-two percent of attackers specifically experienced a financial stressor sometime prior to their attack.

Of the 180 attackers analyzed, researchers found 39% had experienced unstable housing within 20 years of their attacks, including 17% who were experiencing homelessness at the time of the attack, and three assailants who targeted other members of the homeless population.

In the U.S., the number of homeless people is calculated by the Department of Housing and Urban Development. The department counts people on the street and in homeless shelters annually in December. In 2022, that number was 582,462.

Just over one-third of the attackers had a history of using illicit drugs, misusing prescription medications or abusing substances like alcohol or marijuana, which often led to "negative consequences because of their substance use, including criminal charges, professional or academic failures, court-ordered programs, and evictions," according to the report.

According to the Substance Abuse and Mental Health Services Administration, 61.2 million people nationwide ages 12 or older — 22% of the U.S. population — used illicit drugs in the past year, and 9.2 million people misused opioids.

Nearly one-third of the attackers detailed in the Secret Service study had at least one contact with law enforcement that did not result in arrest, including attackers who had engaged in acts of domestic violence (23%), violent crimes (23%) and nonviolent crimes (22%).

4. Over half of attackers experienced mental health symptoms prior to or at the time of their attacks.

"The vast majority of individuals in the U.S. who experience the mental health issues discussed…do not commit acts of crime or violence," the report noted. "The symptoms described in this section constitute potential contributing factors and should not be viewed as causal explanations for why the attacks occurred."

Symptoms found among the 58% of attackers included depression, psychotic symptoms and suicidal thoughts. 

"The age of symptom onset varied, with some attackers first experiencing symptoms in adolescence while others' symptoms began later in life," the report read.

The statistic squares with national estimates. According to the Centers for Disease Control and Prevention, over half of the U.S. population will be diagnosed with a mental health illness at some point in their lifetime.

"Mental health symptoms alone are not a correlation for acting violently," Dr. Alathari said. "In fact, the vast majority of individuals in this country with mental health issues would never become violent, but it is an important factor to consider in the context of assessing an individual that might come to our attention for eliciting concern."

Nearly one-third of the attackers previously received some sort of mental health treatment, though care "varied widely and was often not sustained," according to the report.

5. More than half of attackers were motivated by grievances and sought retaliation for perceived wrongs. 

While grievances most often related to personal stress linked to health, finances, bullying or feelings of victimization, 17% of grievances were related to issues with a current or former domestic relationship and 10% were connected to the workplace.

Analysts concluded that "grievances have remained the most common component to the motives of mass attackers from 2016 to 2020."

And while attackers' ages ranged from 14 to 87, with an average age of 34, nearly all the 180 attackers (96%) in the report were male.

6. One-quarter of the attackers subscribed to conspiracy theories or hateful ideologies. 

These belief systems included anti-government, anti-Semitic and misogynistic views, among others.

At least 35 attackers (19%) displayed misogynistic behaviors prior to attacks — such as sexual harassment, threatening sexual violence and calling women by derogatory names.

Conspiracy theories observed among the attackers included false beliefs "that the moon landing was staged by the government, Jewish people were trying to take over the world, aliens or lizard people were preparing to take over, people of Chinese descent were responsible for the spread of coronavirus, and the U.N. was plotting to disarm U.S. citizens," the report indicated.  

At least six attackers became radicalized in their beliefs through online engagement, though nearly two-thirds of the 180 attackers had an identified presence online, with some posting on blogs or social media.

"Nearly one-quarter were found to have conveyed concerning communications online, such as threats to harm others and posts referencing suicidal ideations, previous mass shootings, violent content, and hate toward a particular ethnic group," according to the report.

7. Three-quarters of the attackers exhibited concerning behavior that caught the attention of family members, friends, neighbors, classmates, co-workers and others.

Researchers determined that nearly two-thirds of the 180 attackers exhibited "objectively concerning or prohibited" behaviors, or shared communications that were so concerning, "they should have been met with an immediate response."

Of those attackers, nearly half — 49 % — exhibit concerning behaviors shared disturbing communications and direct threats, including threats to harm others, threats of domestic violence, references to an impending attack and talk of building or acquiring weapons, among other communications.

The study revealed "half of the attacks involving a business location and the attackers often had a prior relationship with the business, either as a current or former employee, or as a customer."

Analysts stressed that members of the community should engage in proactive bystander reporting and urge businesses to "consider establishing workplace violence prevention plans to identify, assess, and intervene with current employees, former employees, and customers who may pose a risk of violence."

Over 21,000 organizations — including schools, houses of worship, businesses, law enforcement agencies and even sports leagues, like the NBA and MLB — have signed up for virtual training issued by the Secret Service, according to Alathari.

While Wednesday's report does not address this week's mass shootings, Alathari said the events "impact" her team, in part because "we study them day in and day out."

"We want to make sure communities have this information that the Secret Service is putting out," Alathari added. "We have the science. We have the guidance. We want people to use it so that we can try to prevent future, horrific acts of violence."

If you or someone you know is in emotional distress or suicidal crisis, call the National Suicide Prevention Hotline at 1-800-273-TALK (8255).

For more information about mental health care resources and support, The National Alliance on Mental Illness (NAMI) HelpLine can be reached Monday through Friday, 10 a.m. to 6 p.m. ET, at 1-800-950-NAMI (6264) or email

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