Montgomery County police are still trying to determine the ownership of a sawed-off shotgun that killed 18-year-old Timothy Sutton Jr. Wednesday afternoon.

Authorities have tentatively classified the shooting death as accidental, but an investigation is continuing. They say Sutton, described as an "ordinary teenager" who loved basketball, was apparently the latest victim of the deadly combination of lethal weapons and inquisitive youth.

Joyce Sutton, the victim's mother, said the shotgun's existence was well-known among children in the Paddington Square apartment complex in Silver Spring, a collection of low-rise brick buildings off East-West Highway.

"Some guys found the gun in a nearby creek" several days ago, Sutton said. "It was a very tragic discovery."

Maryland law requires handguns to be registered, but Montgomery police said tracing the ownership of shotguns, particularly ones that have been altered, is extremely difficult.

Police said the gun most likely is not registered. Sawed-off shotguns, in which the barrel has been shortened so the weapon can be easily concealed, "are something you make yourself. They don't have a legal use," said police spokeswoman Ann Evans.

Police said Sutton, a former student at Bethesda-Chevy Chase High School, died immediately from a single gunshot wound to the head. Sutton, along with four friends, were "listening to music and hanging out" in an apartment in the 8800 block of Lanier Drive, police said. No adults were present, police said.

The sawed-off shotgun discharged while Sutton and a 16-year-old were in the bedroom, police said. "The kids were playing around with the gun," said Joyce Sutton. "I don't know if they knew it was loaded."

Police said yesterday they have not yet interviewed the 16-year-old, who is being treated for shock at a local hospital. The three other youths were in the front room when the gun went off, police said.

An autopsy is being conducted by the Maryland Medical Examiner's Office in Baltimore. Police also will examine powder burns on the victim's body to determine who fired the weapon, an official said. Authorities found no alcohol or drugs in the apartment.

Joyce Sutton said she visited the apartment shortly before the shooting. By the time she returned to her own apartment in the 8800 block of Lanier Drive, Sutton said she heard the 16-year-old youth screaming, "Mrs. Sutton, I'm sorry. I didn't mean to do it."

Minutes later, Sutton said she saw her son lying on the carpeted bedroom floor "with the right side of his head blown away."