A teenager awaiting trial in the death of a Starbucks manager on a downtown subway concourse is on house arrest, but police say he still managed to commit a crime.

Kinta Stanton, 17, was playing with a gun in the basement of his North Philadelphia house Wednesday when the weapon discharged, police said. The blast struck a 17-year-old friend in the torso, critically injuring him, authorities said. Another teen in the room was uninjured.

Detectives recovered a shell casing but not the gun, said Sgt. Ray Evers, a police spokesman.

"I'm not sure why Stanton was out on house arrest," Evers said. "I have no idea why. But (this shooting) seems to show his propensity to violence."

Stanton was charged Thursday as an adult with assault, reckless endangerment and multiple weapons counts.

He was one of five teens charged in March 2008 in the death of Sean Patrick Conroy. He is charged as a juvenile with third-degree murder in that case, which is scheduled to begin next week.

Defense lawyer Lonny Fish said it was still unclear what really happened in Stanton's home, because the victim's story has changed several times.

"The murder trial is Monday, and that's what I'm focused on," Fish said.

Conroy was chosen at random by the five teens and beaten in the underground concourse near the Starbucks store he managed, police said. He was found on his knees, gasping for air by a transit police officer who saw the assault from across the tracks. He died a short time later.

A medical examiner ruled his death a homicide, saying the assault broke four of his ribs and triggered a fatal asthma attack.