UPDATED: 7:47 p.m.
Police say 19-year-old Tyquan "Fats" Atkinson was picked up Wednesday evening in Chester.
Police believe Atkinson is responsible for shooting and killing of 20-year-old Nicholas Flacco, son of Internal Affairs Chief Inspector Chris Flacco.
Police say Flacco was tailgating after a Phillies game Saturday and was killed trying to break up a fight.
"Basically you had a girl fight, which turned into a guy fight, and then somebody thought it was a good idea to bring a gun into the situation," said Homicide Capt. Jason Smith. The two groups "have had encounters before in the past. One group is from Northeast Philly, and the other is from South Philadelphia. The potential for volatility is there."
Smith said one of the girls in the group called Atkinson to FDR Park. When he arrived, he fired a bullet into Flacco’s chest.