A gunman wearing a bulletproof vest opened fire on the streets of Philadelphia on Monday night, killing four people and wounding two boys in the latest outbreak of gun violence in the United States, police said.

The victims were apparently random, with no connection immediately known between them and the shooter.

The shootings took place over several city blocks in the southwestern neighborhood of Kingsessing. Responding officers chased the suspect as he continued to fire, and he was arrested in an alley after surrendering, Police Commissioner Danielle Outlaw said at a news conference.

“At this point all we know is that this person decided to leave their home and target individuals,” Outlaw said.

He had a bulletproof vest, an “AR-type rifle,” multiple magazines, a handgun and a police scanner, she said.

Officers were flagged down at about 8:30 p.m., and multiple calls of shots fired came in from Kingsessing. Police found some gunshot victims, and as they were attending to them, they heard more gunfire, Outlaw said.

The suspected shooter was identified as a 40-year-old man. A second person was also taken into custody who may have returned fire at the suspect, but police did not know whether there was a connection between the two people, Outlaw said.

The chief described the scene as covering an area of two by four blocks and said dozens of shell casings were found.

“You can see there are several scenes out here,” Outlaw said. “We’re canvassing the area to get as much as we can, to identify witnesses, to identify where cameras are located and to do everything to figure out the why,” Outlaw said.

Three of the dead ranged in age from 20 to 59, while the fourth, who had not yet been identified, was estimated to be between 16 and 21. All were male. The two hospitalized victims are boys, ages 2 and 13. They were in stable condition, Outlaw said.