Police believe there was a fight between two men who knew each other, and at least one of the men had a concealed weapon.
As the men fought over the gun, others joined in the fight, according to a statement released by police on Monday.
Gunshots were fired and hit someone involved with the fight.
Police have identified the armed suspect as a 16-year-old Lancaster City resident.
An uninvolved, legally armed, bystander was in a nearby store and heard the first set of gunshots, police say.
The armed bystander shot at the men, striking one of the suspects, according to police.
When these shots were fired the fight concluded, police say.
The bystander waited at the scene until officers from the Lancaster City Police and Park City Security arrived.
"The District Attorney will be responsible for determining if the actions of the bystander were lawful and justified, upon the completion of the investigation," police said in a statement.
The 16-year-old armed suspect was injured in the shooting and has been hospitalized; he is in police custody, awaiting the filing of formal charges, police say.
Two other men involved in fight for the firearm also suffered gunshot injuries.
A woman walking through the mall with her family and was struck in the arm when the first shots were fired, police stated.
All of the injuries are considered non-life threatening, according to police.
Two of the shooting victims have been released from the hospital as of Monday afternoon, police said in a release.
Six gunshots were fired in this incident from two firearms, both of which were recovered at the scene by police.
Anyone with information please call the Lancaster City Bureau of Police at (717) 735-3301.
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