Lancaster police said the gunfire at the Park City Center was reported just before 2:30 p.m. Sunday.
According to police, the initial fight began between two people who knew each other. At least one of the suspects had a gun, and a struggle began to get a hold of the weapon, police said. Other people joined the fight, too.
According to police, the armed suspect, who has been identified as a 16-year old from Lancaster, shot one of the people involved in the fight. A second gunshot was also fired.
A bystander, armed with their own legally possessed gun, heard the gunshots and fired their weapon, hitting one of the suspects, police said.
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The fight ended and the bystander waited for police to arrive.
The original armed suspect, who was injured in the shooting, was in the hospital in police custody. Police said the suspect is awaiting formal charges.
Two of the other males who were involved in the fight also suffered gunshot injuries. A female who was walking through the mall with her family was struck in the arm when the first shots were fired, police said. All of the injuries are considered non-life-threatening.
Police said they believe a total of six gunshots were fired during the incident.
The District Attorney is currently working to determine if the actions of the bystander were lawful and justified. Charges have not been filed against this person.
The mall reopened to customers on Monday.
Anyone with information on the shooting is asked to call police at 717-735-3301.