After four days of testimony, the jury deliberated for more than two hours before delivering the verdict.
Brandon Meade was arrested for the murder of Agatha Hall after her death was initially ruled a suicide.
Officials said because of increased awareness, reporting could rise.
Police say the victim was beaten to death.
A girl who was caught in the crossfire during a shooting is in stable condition at Temple University Hospital, police said.
Police did not find any explosives after a three-hour search of the building.
Police say they believe the three victims may have been shooting at each other, but are still investigating.
The shootings happened in the same place and almost within 24 hours of each other.
Police said the shooting was an accident and no arrests have been made.
No arrest has been made following Friday morning's TU Alert.