WAUWATOSA, Wis. (AP) — Police in suburban Milwaukee on Monday provided more details about their investigation into a mall shooting last week, including the arrests of two more people.

Gunfire broke out outside Mayfair Mall in Wauwatosa on Friday afternoon. Eight people were injured but none were killed. The shooter fled before police arrived. Police said the shooting stemmed from an altercation and wasn’t a random act.

Authorities announced on Sunday that officers had arrested a 15-year-old Milwaukee boy, whom investigators believed was the shooter.

Wauwatosa Police Sgt. Abby Pavlik said Monday evening that the 15-year-old boy was arrested during a traffic stop in Milwaukee. Officers recovered the weapon they believed was used in the shooting from the vehicle.

Officers also arrested a passenger in the vehicle as well as a third individual believed to have been involved in the shooting. Pavlik did not include any details of the circumstances of that third arrest in an email. She also did not include the ages or names of either person or any of the victims.

Investigators weren’t sure if the shooting was gang-related but were working with prosecutors on potential charges, she said.

The Wauwatosa Police Department plans to add officers at the mall in upcoming weeks to provide an added sense of safety for holiday shoppers, she said.