A shooting at a California home left eight people wounded. Picture used for illustrative purposes only.

The shootings follow a surge in homicides and other violence over the past several years that experts say accelerated during the coronavirus pandemic. They happened in suburban Chicago, Washington state, central Pennsylvania, St. Louis, Southern California and Baltimore.

"There’s no question there’s been a spike in violence,” said Daniel Nagin, a professor of public policy and statistics at Carnegie Mellon University. "Some of these cases seem to be just disputes, often among adolescents, and those disputes are played out with firearms, not with fists.”

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Researchers disagree over the cause of the increase. Theories include the possibility that violence is driven by the prevalence of guns in America, or by less aggressive police tactics or a decline in prosecutions for misdemeanor weapon offenses, Nagin said.

As of Sunday evening, none of the weekend events fit the definition of a mass killing, because fewer than four people died at each location. The figure does not include the shooter. However, the number of injured in most of the cases matches the widely accepted definition for mass shootings.

Associated Press