Police in Philadelphia on Monday were still searching for multiple gunmen after a shooting Saturday left three people dead in one of a dozen mass shootings in a grisly weekend of gun violence in the United States.

The shooting in Philadelphia broke out in a crowded downtown street Saturday night. Police in the area of the popular South Street entertainment district heard gunshots nearby, and one officer saw a gunman firing into a large crowd, Police Commissioner Danielle Outlaw said at a Sunday new briefing.

Outlaw said police believe the shooting may have stemmed from a physical altercation. Two of the people killed were “innocent bystanders,” Outlaw said, while one of the people killed was believed to have been involved in the incident. Eleven other people were wounded as the gunshots broke out.

Police identified Alexis Quinn, 27, and Gregory “Japan” Jackson, 34, as two of those who lost their lives when violence erupted in the entertainment district. Teacher’s union AFT Pennsylvania identified Kristopher Minners, 22, as the third victim.

“We’re absolutely devastated, devastated by this incident,” Outlaw said.

No arrests have been made, and police said five guns were fired; two handguns were recovered at the scene, including one with an extended magazine, which carries more bullets.

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The weekend bloodshed comes after a spate of gun violence in Buffalo, New York, Uvalde, Texas, and Tulsa, Oklahoma, that has rocked the nation in recent weeks and focused renewed attention on gun laws.  

The shooting in Philadelphia was one of at least 12 mass shootings from Friday to Sunday in the United States, according to the Gun Violence Archive, which tracks mass shootings, defined as four or more people injured or killed. 

A shooting at a Chattanooga, Tennessee, nightclub Sunday morning, left two people fatally shot and a third dead after being hit by a vehicle during a scramble following the shooting, Chattanooga Police Chief Celeste Murphy said. Overall, 14 people were hit by gunfire and three were hit by vehicles, Murphy said.

In Saginaw, Michigan, three people were killed in a shooting early Sunday, and two others were wounded, police said. Meanwhile, in Grand Rapids, Michigan, a man was killed and three others were injured in a shooting downtown early Sunday, MLive reported.