Police found a fifth victim in a southwest Philadelphia shooting, hours after a heavily armed gunman wearing a bulletproof vest opened fire on Monday evening, the police said.

The fifth victim was found in a house near the shootings; there were casings that matched the other shootings, according to a police spokesperson.

The dead were all men between the ages of 20 and 59, the police said. Two children, aged 2 and 13, were also hospitalized and were stable, they said.

A male suspect was taken into custody by the police just before 8:40 p.m., the authorities said, adding that they had recovered a semiautomatic rifle, a handgun and another gun in the alleyway behind the 1600 block of South Frazier Street.

A second person who the police believed had “picked up the gun and returned fire in the direction of the shooter” was also in custody, Danielle M. Outlaw, the police commissioner, said at a news conference late Monday night.

“At this point, we don’t see a connection to any of the victims and in the shooter, so we’re still trying to piece it together and figure it out,” Commissioner Outlaw said.

Police officers, who were on foot, arrested the suspect in an alley, she said. The suspect was wearing a bulletproof vest containing “multiple magazines” and had an AR-style rifle, a handgun and a police scanner.

Commissioner Outlaw said she did not know whether the gunman was firing from the handgun or the rifle, but said he was still “actively shooting” when he was taken into custody.

“Thank God our officers responded as quickly as they did,” she said. “I can’t even describe the level of bravery and courage that was shown.”

About 50 spent shell casings were found at the crime scene, which covered a two-by-four-block area, the commissioner said.

According to the police, an officer heard gunfire in the Kingsessing neighborhood just before 8:30 p.m. and found at least one victim near South 56th Street and Chester Avenue.

In recent years, Philadelphia has been plagued by gun violence, with more deadly shootings than far bigger cities. But there have been 212 homicides in 2023 so far, a decline of 19 percent from 2022, according to the Office of the Controller.

The city government has rolled out an array of efforts to address the crisis, including grants for community groups, violence intervention programs and earlier curfews. And it has sued the gun-friendly state legislature for pre-empting its authority to enact stronger local gun laws, like reporting requirements for lost or stolen guns. But the sheer number of guns in the city has made the problem difficult to tackle.

In a statement released on Monday evening, the Philadelphia Federation of Teachers called on elected officials to act on gun reform.

“Again and again, the devastation wrought by the scourge of gun violence continues to rip families apart and leave communities shattered,” Jerry Jordan, the president of the federation, said in a statement.

Emma Hilton, 70, who lives on 56th Street, where shots were fired, said the shooting is the third she has experienced in the 11 years she has lived in the neighborhood.

“I’m getting ready to get out of here,” she said on her front porch a few feet from where the police commissioner gave her statement to reporters. “It’s bad around here.”

The shooting was the latest this year of at least 343 incidents across the nation in which four or more people were injured or killed, according to the Gun Violence Archive. The organization has documented more than 600 mass shootings in the United States in each of the last three years.

Amy Harmon contributed reporting.