A tragic incident at a children’s birthday party in California over the weekend, resulting in four fatalities, marked the 17th mass killing of the year. This figure is the lowest recorded since 2006, as per data compiled by The Associated Press and USA Today in collaboration with Northeastern University.

Despite this decrease, experts caution that it may not signal a long-term trend towards greater safety. Instead, it might simply reflect a return to typical levels of such incidents.

Criminologist James Alan Fox from Northeastern University noted, “While Sir Isaac Newton didn’t study crime, his principle of ‘what goes up must come down’ applies here.” He suggests that the current decline is likely what statisticians refer to as “regression to the mean,” indicating a normalization after the unusual spikes in mass killings witnessed in 2018 and 2019.

Fox added, “Will we see a decline in 2026? I wouldn’t count on it. What decreases can also increase again.”

The definition of mass killings used in this data involves instances where four or more people are killed within a 24-hour period, excluding the perpetrator. According to the database managed by Fox, mass killings have decreased by approximately 24% this year compared to 2024, which itself saw a roughly 20% decline from the numbers recorded in 2023.

Mass killings are rare, and that means the numbers are volatile, said James Densley, a professor of at Metropolitan State University in Minnesota.

“Because there’s only a few dozen mass killings in a year, a small change could look like a wave or a collapse,” when really it’s just a return to more typical levels, Densley said. “2025 looks really good in historical context, but we can’t pretend like that means the problem is gone for good.”

Decline in rates of homicide and violent crime might be a factor

But there are some things that might be contributing to the drop, Densley said, including an overall decline in homicide and violent crime rates, which peaked during the COVID-19 pandemic. Improvements in the immediate response to mass shootings and other mass casualty incidents could also be playing a part, he said.

“We had the horrible Annunciation School shooting here in Minnesota back in August, and that case wouldn’t even fit the mass killing definition because there were only two people killed but over 20 injured,” Densley said. “But I happen to know from the response on the ground here, that the reason only two people were killed is because of the bleeding control and trauma response by the first responders. And it happened on the doorsteps of some of the best children’s hospitals in the country.”

Crime is complex, and academics are not great at assessing the reasons behind crime rate changes, said Eric Madfis, a professor of criminal justice at University of Washington-Tacoma.

“It’s multicausal. It’s never going to be just one thing. People are still debating why homicide rates went down in the 1990s,” Madfis said. “It is true that gun violence and gun violence deaths are down, but we still have exceedingly high rates and numbers of mass shootings compared to anywhere else in the world.”

More states are dedicating funding to school threat assessments, with 22 states mandating the practice in recent years, Madfis said, and that could be preventing some school shootings, though it wouldn’t have an impact on mass killings elsewhere. None of the mass killings recorded in the database so far in 2025 took place in schools, and only one mass killing at a school was recorded in 2024.

Most of those who die in mass killings are shot

About 82% of this year’s mass killings involved a firearm. Since 2006, 3,234 people have died in mass killings — and 81% of them were shooting victims.

Christopher Carita, a former detective with the Fort Lauderdale Police Department and a senior training specialist with gun safety organization 97Percent, said the Safer Communities Act passed in 2022 included millions of dollars of funding for gun violence protection programs. Some states used the money to create social supports for people at risk of committing violence, and others used it for things like law enforcement and threat assessment programs. That flexibility has been key to reducing gun violence rates, he said.

“It’s always been framed as either a ‘gun problem’ or a ‘people problem’ and that’s been very contentious,” Carita said. “I feel like for the first time, we’re looking at gun violence as a ‘both, and’ problem nationally.”

Focusing on extreme events like mass killings runs the risk of “missing the forest for the trees,” said Emma Fridel, an assistant professor of criminology at Florida State University. “If you look at the deaths from firearms, both in homicides and suicides, the numbers are staggering. We lose the same number of people every year to gun violence as the number of casualties we experienced in the Korean War. The number one cause of death for children is guns.

“Mass killings should be viewed as one part of the issue, rather than the outcome of interest,” she said.