PHILADELPHIA (CBS) — A mass shooting on Philadelphia’s South Street left three people dead and 12 others injured. Eleven of the 12 people injured were shot, according to police. The other person was injured by shattered glass.

At a press conference on Sunday, Philadelphia police commissioner Danielle Outlaw said one of the three victims who died in the shooting was involved in a physical altercation with another man. She said they believe that altercation was potentially the genesis of the shooting. 

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Outlaw said the men began firing at each other and both were struck. The 34-year-old involved in the altercation was pronounced dead at the hospital at 12:05 a.m., but the other man was wounded. The 34-year-old was identified as Gregory Jackson by police. 

Police believe the other two people who died and most of the people injured were not involved in the initial incident.  

The two others killed were identified as 24-year-old Alexis Quinn and 22-year-old Kris Minners, a second grade resident advisor of Girard College. They were both pronounced dead at Jefferson Hospital just before midnight Sunday.

Nine of the 11 people injured in the shooting were 23 or younger. 

Police say a 23-year-old man was shot multiple times in the torso area and placed in critical condition. An 18-year-old man was shot once in his right hand, while another was shot in his left buttocks. 

According to police, a 20-year-old man was shot in his left forearm and another was hit in his left shoulder.

Three teenagers – a 17-year-old boy and two 17-year-old girls – were all shot during the incident, police say. 

A 69-year-old woman was shot in her left calf area, while a 43-year-old man was hit in his right ankle. 

A 19-year-old woman was shot once in her left leg.  

Police say a 49-year-old woman was struck by shattered glass and injured during the shooting.

“Yesterday was a dark day for Philadelphia,” Outlaw said. “While many of us were out enjoying the beautiful day in the city, a horrendous and unthinkable act happened in a very popular local tourist hang out.”

Police say patrol officers in the area heard numerous gunshots coming from the 200 block of South Street just before midnight Saturday.

Multiple shooters reportedly fired into a crowd of people on South Street.

Inspector D F Pace says one of the officers witnessed the shooting firsthand and quickly fired at one of the shooters, causing them to drop their weapon. Police say they spotted the shooter on the corner of South and American Street.

Police believe they struck the gunman due to the suspect dropping their weapon, but he was able to escape the area. Police say he was last seen heading southbound on the 600 block of American Street. He was lost in the area.

Police were able to recover two guns at the scene, one with an extended magazine.

“He was within 10 to 15 yards of the shooter watching this person shoot into the crowd when the officer engaged that shooter and as a result of that brave officer, that individual, again we’re uncertain if he was struck or not, but the officer was able to get that individual to drop his gun and flee,” Insp. D F Pace said.

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Police say based on their evidence, there were at least five different guns fired during the shooting.

Police described it as a terrifying and chaotic scene.

Philadelphia Mayor Jim Kenney issued a statement following the mass shooting reading in part:

The events that transpired last evening on South Street are beyond devastating. Once again, we see lives lost and people injured in yet another horrendous, brazen and despicable act of gun violence. Our city and country have experienced a steep rise in gun violence over the past few years. We’ve spent these years grappling with this epidemic—doing everything not only to stop it but to try to understand why the violence continues—it’s senseless, needless and deeply troubling. I know this shooting has shaken our community. The safety of our residents and visitors is our top priority. Our administration, in partnership with our local and federal law enforcement agencies, continues to work relentlessly to reduce violence and create safer communities.

The mayor also says his “heart is with the family, friends and loved ones of those lost or injured, and with everyone impacted by this terrible tragedy.”

CBS3 spoke to a neighbor who lives close to the shooting. She says she was in bed when she heard the gunfire. When she woke up Sunday morning and read that there was a mass shooting, she was left full of emotion.

Detectives are still searching for three of the guns fired during the exchange as officials were left to answer questions if enough was done to prevent the mass shooting. 

“The crowd itself started to get a little bit more dense around 8 o’clock,” Chief James Kelly said. 

A video from the scene shows a large pool of people gathered on 3rd and South Streets moments before the shooting happened. And then, everyone ran for cover once the shots rang out.  

“We did have double the presence and second and south was probably the heaviest,” Kelly said. 

We pressed officials if anything was done to try to disperse that crowd

“We do keep the crowds moving, but at the same time, we have to be cognizant of people’s rights to come down there and to walk around so it’s a balancing act,” Kelly said. 

“If we’re going to continue to allow that lawlessness to continue and say, ‘That’s their right to do that and they’re really not bothering anybody.’ Then, we’re going to continue to have these incidents,” city councilmember Mark Squilla said.

Police tell Eyewitness News that the shooting that happened on 3rd and South Streets was one of three that happened in a two-hour period. One of them happened in the 500 block of South Broad Street. One man died in that shooting. Police are looking into whether that shooting is connected to the one on South Street.

Sources have told Eyewitness News officers initially deployed to the South Street area were pulled to Citizens Bank Park due to a brawl that happened after the Phillies game.

CBS3 has also learned that officers from neighboring districts will be pulled into the Center City area to help monitor and ensure safety. 

Authorities are offering a $20,000 reward for information in the case.

For a list of gun violence resources in Philadelphia, click here.

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CBS3’s Ross DiMattei, Alicia Roberts, Alyssa Adams and Tom Ignudo contributed to this report. Stay with CBSPhilly.com, CBS3, and CBS News Philly for continuing coverage of this developing story.