WASHINGTON, Dec 2, (AP): A shooting last weekend at a children’s birthday party in California that left four dead was the 17th mass killing this year - the lowest number recorded since 2006, according to a database maintained by The Associated Press and USA Today in partnership with Northeastern University. Experts warn that the drop doesn't necessarily mean safer days are here to stay and that it could simply represent a return to average levels.

"Sir Isaac Newton never studied crime, but he says ‘What goes up must come down,'" said James Alan Fox, a criminologist at Northeastern University. The current drop in numbers is more likely what statisticians call a "regression to the mean,” he said, representing a return to more average crime levels after an unusual spike in mass killings in 2018 and 2019.

"Will 2026 see a decline?" Fox said. "I wouldn’t bet on it. What goes down must also go back up.” The mass killings - defined as incidents in which four or more people are killed in a 24-hour period, not including the killer - are tracked in a database maintained by The Associated Press and USA Today in partnership with Northeastern University.

Fox, who manages the database, says mass killings were down about 24% this year compared to 2024, which was also about a 20% drop compared to 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.” 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.