Only Action News was there as a man identified as Rashaan Vereen was taken into police headquarters on Monday night.
He is one of two men charged by the District Attorney's Office Monday in connection to Saturday night's shooting.
U.S. Marshals made the arrest in the 2300 block of Hemberger Street in South Philadelphia.
"Mr. Vereen was wanted for attempted murder, aggravated assault, and firearms related offenses," U.S. Marshal Supervisor Deputy Rob Clark said.
A second suspect, Quran Garner, 18, who is currently in custody, is charged with multiple offenses, including aggravated assault and aggravated assault on law enforcement. He did not have a license to carry a gun, Assistant District Attorney Joanne Pescatore said.
Among the three people killed were two innocent bystanders, identified as 22-year-old Kristopher Minners and 27-year-old Alexis Quinn.
The third person killed has been identified as 34-year-old Gregory "Japan" Jackson.
Of the 11 wounded, a man identified as Mika Townes remains in serious condition.
The District Attorney's Office said both Jackson and Townes had a license to carry.
Surveillance video obtained by ABC News and 6abc shows what unfolded at about 11:30 p.m. Saturday on South Street.
In the video, Jackson and Townes are seen exchanging words. Then Jackson pulls a gun.
The video shows Jackson and Vereen beating Townes. Then there's a gunfire exchange. Both Townes and Jackson are hit.
"Gregory Jackson shoots at Mika Townes first. Mika Townes returns fire, killing and shooting Gregory Jackson," Pescatore said.
Police sources confirm Vereen is the man seen in the video picking up Jackson's gun and passing it off to someone in a blue hoodie. Then he stays with Jackson.
The second arrest warrant issued by the District Attorney's Office was for Garner, who investigators said was seen on video in a group of people prior to the shooting.
"Quran Garner is on video shooting back toward the area where the initial confrontation takes place between Gregory Jackson and Mika Townes, who is a victim in this particular case. (Quran Garner), it's our belief, was a friend or was with Mika Townes when this initial altercation starts," Pescatore said.
"After the initial altercation, guns are drawn by Gregory Jackson and Mika Townes. Gregory Jackson shoots at Mika Townes first. Mika Townes returns fire, shooting and killing Gregory Jackson. As a result of that, Quran Garner then begins to fire down the street towards South Street, towards where the initial confrontation took place."
Officials said officers assigned to the 200 block of South Street heard the initial gunfire and quickly responded.
Investigators said Garner then pointed his gun at police. Officers fired and hit his hand.
"It is at that point that Philadelphia police began to shoot after Quran Garner pulls a gun, has gone out and looks in their direction. They shoot at him, shooting his hands. He's currently at Thomas Jefferson University Hospital undergoing surgery for a result of injury sustained when the police shot back at him," Pescatore said.
Pescatore said Garner used a ghost gun with an extended magazine. It was left at the scene.
Townes remains hospitalized for serious injuries.
Pescatore said both Jackson and Townes did have a license to carry.
The DA's Office said they believe several of those connected to the shooting are part of the local boxing scene.
On Monday morning, District Attorney Larry Krasner said at least four guns - three 9mm weapons and one 40-caliber firearm - were involved in the mass shooting. He said it is possible there are more firearms involved.
DA Krasner provides update on South Street mass shooting
Krasner called the scene 'chilling,' having visited it the next morning after the mass shooting.
"No less chilling is that it happened in more than 10 places around the country over the space of a few days," Krasner said. "It is enough."
Authorities said the officer who discharged his weapon is a three-and-a-half-year veteran of the Philadelphia Police Department. He is assigned to the 18th District. As per protocol, the officer has been placed on administrative duty pending the outcome of the investigation.
The victims
Many of the shooting victims, who ranged in age from 17 to 69, are believed to have been innocent bystanders, Philadelphia Police Commissioner Danielle Outlaw said.
Philadelphia police provide update on deadly mass shooting on South Street
Minners was a second-grade resident advisor at Girard College and a member of the Girard College Federation of Teachers. Girard College is a boarding school in Philadelphia for students grades 1-12.
Close friends and colleagues said he was out celebrating his 22nd birthday when he was shot and killed.
"Our hearts are heavy today with the passing of Kris Minners, a second-grade boys' resident advisor at Girard College and member of our union, yet another victim of senseless gun violence. Our thoughts are with Mr. Minners' family who woke up this morning missing someone at their breakfast table, his colleagues who will be without a friend, and with his students who will be without a mentor and a role model," said the union in a statement.
SEE ALSO: What we know about victims killed in South Street mass shooting
Outlaw called it "a dark day" for the city when many people out enjoying a beautiful day were victims of "horrendous and unthinkable acts ... in a very popular local and tourist hangout."
"It's important that we bring justice to the victims, their families and our community," Outlaw said.
Raw video: Scene of mass shooting in Center City Philadelphia
'Beyond devastated'
In Reno, Nevada at the Annual Meeting of the United States Conference of Mayors, Mayor Jim Kenney issued a statement Sunday morning saying he was 'beyond devastated' by this shooting.
In a one-on-one interview with Action News, he spoke about the city's gun problem.
"It's gotten to the point where there's no price to pay for carrying illegal guns, so people carry them because they don't think anything is going to happen," said Kenney, who was on his way back to Philadelphia.
Kenney said it's up to state and federal officials to enact tougher gun laws, but said he has no confidence they will.
Mayor Jim Kenney Reacts to South Street Shooting
Protesting the violence
A day after the shooting, anti-violence groups gathered on South Street, calling for an end to the bloodshed.
One of the people passing out flyers and offering support was Wali Smith with the Philadelphia Anti-Drug/Anti-Violence Network.
"A lot of them are pretty disturbed because they're trying to make a living for themselves, and things like this make the people afraid to come out and shop," said Smith.
Anti-violence groups gather on South Street after mass shooting
Survivor speaks out
The sheer number of victims meant rescuers had to transport them to three different hospitals, including Thomas Jefferson University Hospital.
Action News spoke with one of the survivors, Jon Johnson, outside the hospital on Sunday morning. He had been shot in the foot.
"You had some sick maniac, I don't know who it was because my back was turned, and he started shooting at everybody," Johnson said. "Some people made it, some people didn't. Me, personally, I seen two people die right in front of my face."
Bolstering resources
South Street is known for its entertainment venues and nightlife with multiple bars, restaurants and businesses. Video posted on social media showed scores of people milling about on the sidewalks and in the street, then fleeing as the gunfire broke out. Police were seeking video surveillance footage from businesses in the area.
The area between Front and 6th streets from Bainbridge to Lombard was closed to pedestrian and vehicular traffic on Sunday night and into Monday morning following the shooting. The area has since reopened.
Anyone with information or video involving the deadly shooting is asked to contact the Philadelphia Police Department at 215-686-TIPS.
The Associated Press contributed to this report.