He said he did not believe the shooting was gang-related, and that it was probably an “isolated incident” stemming from a “personal dispute.”

“It’s a terrible tragedy and frankly an incredible act of cowardice,” Lori Lightfoot, the mayor of Chicago, said at a later news conference on Sunday.

Chief Waller said the victims had “various gunshot wounds to their bodies.” The youngest was 16, he said, and the oldest was about 48. He said four people were critically injured and the rest were in stable condition.

Chief Waller said surveillance footage captured part of the shooting, which took place on the 5700 block of South May Street. After gunshots were fired during a dispute inside the home, people began spilling outside, and two gunmen fired on the crowd, he said.

“It looked like they were just shooting randomly at people as they exited the party,” he said.

Stephanie D. Coleman, the alderman who represents the neighborhood, told reporters that she had gone to the scene after hearing about the shooting from constituents.