(CNN) -- Police searched for a young man Saturday after a shooting left two students wounded at a Philadelphia school a day earlier.
The shooter was in the gym with seven other students at Delaware Valley Charter High School, said city police Commissioner Charles Ramsey.
Some were playing basketball and others standing in a corner when he pulled a gun and fired.
The victims, a boy and a girl, both age 15, were hit in the arm. They were taken to a local hospital, police said, and their wounds are nonlife-threatening.
The Friday afternoon incident was at least the second shooting at or near a school this week in the Olney neighborhood.
The school went into lockdown as law enforcement officers searched students and let them out of the school, said police Lt. John Stanford.
The shooter had left the scene.
Not long after the lockdown, Philadelphia police posted a message on Twitter, saying they had a suspect in custody. They later released the 17-year-old male, who was "completely cleared by investigators," Stanford said.
Police searched for two more young men, both students at the charter school.
One turned himself in Friday but the other one was still on the run, police said.
It unclear if either of them is the shooter. No one had been charged as of Friday night.
"We don't know the motives," Ramsey said, "don't know if it was an accident, don't know if it was intentional."
Surveillance video captured the incident, Stanford said. But police do not know how many shots were fired, his colleague Ramsey said. One bullet could have struck both victims. No shell was found at the scene.
Police were still searching for the weapon late Friday in trash cans, along railroad tracks and other spots around a nearby major urban transit station, transit spokesman Andrew Busch said.
Commissioner Ramsey seemed frustrated about school shootings reported across America.
"People send their kids to school; they shouldn't have to pick them up at the hospital," he said. "These kind of things just absolutely should not happen."
CNN's Greg Botelho contributed to this report.
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