Arrest made in shooting of 13 people at memorial party for man killed by gun violence People ran from gunfire inside the party only to be shot outside, police said.

An arrest has been made stemming from the shooting of 13 people at a pre-Christmas memorial party for a man who was gunned down earlier this year, police said on Monday.

Chicago police said Marciano White, 37, was arrested on a charge of unlawful use of a weapon by a felon following the barrage of gunfire that broke out early Sunday morning at a crowded house on the city's South Side.

Investigators are still trying to determine how many people fired guns at the gathering to celebrate what would have been the 23rd birthday of a man police said was fatally shot in April when he attempted to carjack an armed victim.

It remains under investigation whether White was among those who fired shots inside and outside the house in the Englewood neighborhood about 12:34 a.m. on Sunday.

Among the 13 people wounded was a 16-year-old boy, who was in critical but stable condition.

"It's a terrible tragedy and, frankly, an incredible act of cowardice," Chicago Mayor Lori Lightfoot said during a news conference on Sunday outside the University of Chicago Medical Center, where she visited victims and their families.

The shooting came just three days before Christmas on what was another violent weekend in Chicago in which a total of 38 people were shot and five were killed in a multitude of incidents across the city, authorities told ABC Chicago station WLS.

"We can't normalize this kind of behavior and tragedy in our city," Lightfoot said.

People attending the memorial party for Lonell Irvin fled the house when gunfire erupted inside only to be shot when they got outside, said Fred Waller, chief of bureau patrol for the Chicago Police Department.

"Looks like they were just shooting randomly at people as they exited the party," Waller said.

At least two men were seen on video from security cameras firing handguns outside the event, Waller said.

"One of the people we believe exited that residence ... began to fire at people as they left the residence," Waller said.

One of the gunmen was seen on video opening fire on a vehicle that was passing the house just as panicked partygoers were spilling onto the street, he said.

Investigators spent most of Sunday combing over three different shooting scenes, one inside and two outside the house, according to Waller.

We can't normalize this kind of behavior and tragedy in our city

Many of those attending the party were women and young people, some who had come from out of state, Lightfoot said.

The shooting unfolded when a personal dispute erupted at the house party, Waller said.

The victims shot at the party ranged from age 16 to 48, Waller said. In addition to the teenager, three other victims were listed in critical but stable condition.

Two "persons of interest" were initially detained for questioning, including a man who was armed with a revolver and another who was among the people shot, according to Waller, adding that the wounded man being questioned is possibly the person who initially provoked the dispute.

Police were first alerted to gunfire at the house party by ShotSpotter technology, Waller said.

Officers arrived within three minutes to find a "chaotic scene" and immediately began administering first aid to victims laying on the ground outside the house on South May Street.

Mayor Lightfoot suggested that potential witnesses were not cooperating due to fear of retaliation.

"People in that house know what happened and we've urged them to overcome their fears and come forward with information so that the police can do their job in tracking down the people who were responsible," Lightfoot said.

Lightfoot said the police department is boosting patrols in troubled neighborhoods of the city due to escalating gun violence over the unseasonably warm weekend.

The mayor had a warning for anyone suspected of using guns to settle disputes: "We're coming for you," she said. "We're not going to tolerate this."

She described victims wounded in the mass shooting at the house party as being in tremendous physical and emotional pain.

"One of the victims specifically said to me, 'I just want to know who did this. I want to make sure they are brought to justice,'" Lightfoot said.

ABC News' Alexandra Faul and Ahmad Hemingway contributed to this report.