Two people are in custody after a Sunday morning shooting left 13 injured, four critically, at a Chicago memorial for a man killed earlier this year, police said.

The shots began about 12:35 a.m. after a “verbal altercation” in a home in the city’s South Side, police said, and continued as people fled a party that was meant to mark the birthday of a 22-year-old who was fatally shot in April. Lonnell Irvin was allegedly attempting to carjack a BMW when the driver, who had a concealed-carry permit, shot him in the head, the Chicago Tribune reported.

Sunday’s shooting, which Chief of Patrol Fred Waller called an “isolated incident,” unfolded in a city that has struggled to curb high rates of gun violence amid national scrutiny, though homicides have dropped since a dramatic peak in 2016. Police say shootings in the city are on track to decrease again this year, but Sunday’s tragedy raised familiar frustrations among residents and local officials.

“Very sad and very disappointed that our children, this is their welcoming into not only the Christmas holiday but to their Christmas break,” the city’s 16th Ward alderman, Stephanie Coleman, told reporters, recalling how eight calls from block residents led her to the grim scene in the Englewood neighborhood — where the early-morning chaos brought kids outside.

“I saw disappointment, I saw frustration, I saw, oh gosh, fear,” Coleman said. “I saw lots of concerned neighbors getting to the bottom of it.”

Two people appeared to be “shooting randomly at people as they exited the party” after the dispute broke out, Waller said at a news conference. He said someone also shot at a vehicle as it drove by.

“It’s a chaotic scene,” Waller said.

The party was held in a vacant upstairs unit on the 5700 block of South May Street, Coleman said. She said she did not know more about how the apartment became the location of the gathering.

Waller said those who were hospitalized with gunshot wounds ranged in age from 16 to 48. Four people were in critical condition. Police said the youngest victim had stabilized after wounds to the back and chest left him critical.

Police are questioning two people, one who was shot and another who had a revolver, Waller said. One of them is a 25-year-old man who went to a hospital with “serious” injuries. The shooting did not appear to be gang-related, but Waller said he did not know what caused the dispute.

Cameras captured part of the violence, and technology that alerts officers to the sounds of shots brought authorities to the scene within minutes, Waller said. He said police planned to increase their presence in the area in the coming days.

Mayor Lori Lightfoot (D) at a news conference urged people with information about the shooting to come forward.

“That is the only way that we’re going to bring down violence across our city, is if people come together and step up and say that they’re not going to tolerate this kind of bloodshed at any time of the year, particularly in the holiday season,” she said.

Area resident Terence Daniely told the Chicago Tribune that he woke to see a street filled with cars and ambulances. The 57-year-old lamented the “reckless” violence on the block, where he has spent about four years.

“How does it continually happen?” Daniely told the Tribune. “When is it going to stop?”

It wasn’t the first time that a Chicago memorial to a shooting victim ended in more violence: Gunfire at a 2017 vigil wounded a 12-year-old boy and six others, the Tribune reported. A spike in crime the year before, when Chicago’s homicides topped those in New York and Los Angeles combined, was already sparking renewed national attention — including from President Trump, who has called throughout his term for action to address the “carnage.”

Trump criticized Chicago’s law enforcement at a national gathering of police chiefs this fall, targeting the police superintendent, who said he chose not to attend the event because it “doesn’t line up with our city’s core values.” The president called the Chicago violence “embarrassing to us as a nation,” claiming the country’s third-largest city is less safe than Afghanistan and suggesting without details that its crime rates could easily be brought down.

Police have pushed back on Trump’s statements, pointing to double-digit decreases in crime in recent years. Discussing the president’s address, then-police Superintendent Eddie Johnson — fired this month over what Chicago’s mayor called “ethical lapses” — rebuked “the national narrative that Chicago is a city on fire.”

Johnson also repeatedly disputed the idea that there’s an easy fix for the violence in the city.

“If you have a magic bullet to stop the violence anywhere, not just in Chicago but in America, then please, share it with us,” he said once in response to the president.

Read more: