Police are seeking a third suspect in the South Street mass shooting who may have killed a bystander

Philadelphia police on Tuesday released video images of a man they say fired a .40-caliber handgun into a panicked crowd during Saturday’s mass shooting on South Street, possibly striking at least one of the two bystanders killed in the chaos.

Investigators had not identified the suspect as of Tuesday evening, but the Police Department hopes the images might generate tips that lead to his arrest.

Chief Inspector Frank Vanore said the videos appeared to show the gunman firing shots on the 300 block of South Street just after 11:30 p.m. Investigators believe he fatally shot 24-year-old Alexis Quinn, a home health aide who collapsed at the intersection of Third and South Streets. But Vanore said detectives were awaiting the results of ballistics tests to confirm that theory.

The gunman’s shots came moments after two men had fired at each other a block away, Vanore said. As a large crowd panicked, Vanore said, the gunman on the 300 block began shooting east on South Street. It was not known why he fired or whether he knew anyone involved in the initial gunfight, Vanore said: “He could be someone just firing because people are firing.”

The photo release was the latest development in the investigation into Saturday’s melee, which left three people dead and 11 wounded — more victims than any single episode of gun violence in Philadelphia in at least seven years.

» READ MORE: What to know about the South Street shooting: The victims, investigation, and response

Two people — including a teen suspected of firing a homemade ghost gun — were apprehended Monday and expected to be charged with crimes including attempted murder. But neither had been arraigned as of Tuesday night, court records show.

As police and prosecutors continued gathering evidence, Mayor Jim Kenney and Commissioner Danielle Outlaw toured South Street and met with business owners. Kenney — making his first public appearance since the bloodshed — said the city was “doing everything it can” to respond to an ongoing gun violence crisis, and he often displayed frustration while speaking to reporters.

“If people are hiding their guns and run into each other and want to be violent, I don’t know what else a police officer could do,” he said.

Authorities said Saturday’s shooting began when a confrontation between two groups of men on the 200 block of South Street devolved into a gunfight.

Gregory Jackson, 34, a former professional boxer and youth coach, was the first to pull a gun, prosecutors said Monday, firing at Micah Towns, 23, whom prosecutors said was also a boxer. It was not clear if the two men knew each other, or what their conflict was about.

After Jackson shot Towns, prosecutors said, Towns — while lying in the street — shot back and killed Jackson.

One of Jackson’s friends, Rashaan Vereen, who’d also participated in the brawl, then tried to help Jackson while passing his gun off to other people nearby, prosecutors said.

As crowds in the area panicked, prosecutors said, 18-year-old Quran Garner — an ally of Towns’ who was standing across the street — began firing wayward shots from a ghost gun with an extended magazine.

Police arrived and an officer noticed Garner firing his weapon. The officer returned fire, striking Garner in the hand and causing him to drop the gun and run away, prosecutors said.

Shortly after that, police said, as pandemonium swelled in the crowd, the gunman on the 300 block of South Street began firing his .40-caliber, possibly striking Quinn.

One other bystander — Kristopher Minners, 22, a second-grade boys’ resident adviser at Girard College — was also fatally struck, police said.

Vanore said at least one other gunman, who also has not been identified, was suspected of firing a 9mm handgun from a point farther west on South Street as people screamed and ran.

» READ MORE: Kenney says Philly is ‘doing everything it can’ as probe into South Street mass shooting continues

Ballistics tests should be able to help determine which shots killed Quinn and Minners, Vanore said, in addition to possibly providing clues about whose shots struck the surviving victims.

Garner, the teen who fired the ghost gun, was taken to a hospital Monday by police who were unaware of his role in the gunfire. Still hospitalized, he was arrested Monday and was expected to be charged with crimes including attempted murder for firing into a crowd, prosecutors said.

Vereen — the friend of Jackson’s who participated in the brawl — was arrested on Hemberger Street, near 23rd and Wolf Streets, in South Philadelphia on Monday night. He was expected to face similar charges for his role in the brawl with Towns.

Prosecutors said they did not expect to charge Towns with killing Jackson, saying he’d acted in self-defense after being attacked and shot.