(CNN) -- A young male pulled a handgun Friday afternoon inside a Philadelphia high school gymnasium, firing and hitting two fellow students, police said.
The injured boy and girl, each 15, were transported in stable condition after being shot in the arm just before 3:30 p.m., Philadelphia police Lt. John Stanford said.
The students were among about seven in the Delaware Valley Charter High School gym at that time -- some playing basketball, others in one corner -- according to city police Commissioner Charles Ramsey.
"The suspect is part of that group," Ramsey said.
Both victims appeared to have been struck once inside the gym of Delaware Valley Charter High School, said Stanford. Ramsey said that authorities didn't know yet if they were struck by the same bullet or more than one, noting that no shell was found at the scene.
He described their wounds as non-life threatening.
The school went into lockdown as law enforcement officers cleared it and hunted for the suspect, who had left the building, according to Stanford.
The police lieutenant said students were searched and then let out of the school. He also said surveillance video had captured the incident.
A short time later, Philadelphia police tweeted they had a suspect in custody. Officer Jillian Russell, a police spokeswoman, said he was 17 years old.
Ramsey later said authorities were able to "identify him right away," after which officers were sent to his home.
"We were able to grab him," the police commissioner said. "We did not recover the gun, but we do have him in custody and he has been positively identified."
But a few hours later, Stanford said that young man was not the shooter as police initially thought, though he was at the scene. He was "completely cleared by investigators and released" later that night, the police lieutenant said.
By then, Philadelphia police had announced they were "still looking for additional suspects." This includes searching for a weapon possibly used in the shooting in trash cans, along the tracks and other spots around the Southeastern Pennsylvania Transportation Authority's Olney station, SEPTA spokesman Andrew Busch said.
While a gun hadn't been found by 9 p.m., Stanford said one of the two young males authorities had been looking for had turned himself in. A third male wanted by police had been expected to do the same but had not turned himself in as of 10:45 p.m., added the police spokesman.
All three youths are Delaware Valley Charter High School students. It is not clear if any of them are, in fact, the shooter. No one had been charged as of Friday night.
Asked about what might have prompted the shooting, Ramsey said, "We don't know the motives -- don't know if it was an accident, don't know if it was intentional."
Located in the Olney section of Philadelphia, Delaware Valley Charter High School is open to any student who lives in the city.
In its 2011 annual report to the state Department of Education, the school noted that it moved into its new facility in June 2006 and reported significant growth in reading and math test scores in recent years.
Friday's incident was at least the second shooting at or near a school this week.
In New Mexico on Tuesday, a 12-year-old student with a sawed off, 20-gauge pump shotgun opened fire in a crowded gymnasium at Berrendo Middle School, according to authorities. Two students were seriously injured and the shooter was in custody.
Ramsey, the Philadelphia police commissioner, acknowledged that such shootings are "happening across our country all too often, and it's just got to stop."
"(When) people send their kids to school, they shouldn't have to pick them up at the hospital," Ramsey added. "I mean, these kind of things just absolutely should not happen."
CNN's Jason Carroll, Poppy Harlow, Cristy Lenz, Haley Draznin, Kevin Conlon and Ray Sanchez contributed to this report.