It happened on March 26 outside of the Golf and Social Club on Delaware Avenue around 8 p.m.
In video released by police, you can see the two suspects walk up and unleash a barrage of bullets into the gathering crowd.
Police say a 16-year-old male suspect was arrested on July 27 after officers were able to track him to a vehicle used before the shooting.
He is facing seven counts of attempted murder
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Three of the seven victims were teenagers. At least four of the victims were seriously injured in the violence, police said.
"We've always believed that people (knew) who was involved. We got one of them," said Deputy Commissioner of Investigations Ben Naish on Wednesday.
Police say a second suspect remains at large. Anyone with any information is asked to call police at 215-686-TIPS.
Naish said the teen was captured with help from the Cheltenham Police Department, Norristown Police Department, Montgomery County Probation Department and the Pennsylvania State Police.