A Southeast Washington man was arrested yesterday and charged with killing a 13-year-old boy in a shooting that authorities said was probably accidental.

Police said Pernell P. Wood apparently mishandled a gun at a Southeast Washington apartment when it fired Monday morning, killing Michael Swann. Wood, 20, turned himself in yesterday afternoon and was charged with second-degree murder.

Details emerged yesterday that indicate Michael was a victim of carelessness, although detectives cautioned that they are continuing to interview witnesses and piecing together what occurred.

At the time of the shooting, Wood was visiting a girlfriend's apartment in the 2600 block of Douglas Road SE, police said. Michael also was there, visiting a friend and skipping classes, police said yesterday.

Police said Wood was alone in a bedroom when the gun fired about 10:45 a.m., sending a single round through a thin wall and into a bedroom. Michael, who was in that room with three other people, was struck in the side, police said.

Wood told detectives that the gun was on a bed and that it went off when he jumped onto the mattress, according to police. Although investigators do not believe that he deliberately fired the weapon, they said they were skeptical about his explanation.

Capt. C.V. Morris, head of the D.C. police violent crimes unit, said the shooting probably was an accident but was still considered second-degree murder.

"It appears he was negligently handling a weapon in the bedroom and somehow it went off and the bullet went through the wall and hit the victim," Morris said. "He was the only person in the room at the time. There was no argument between the two of them that might indicate real foul play."

Wood, of the 2800 block of Jasper Road SE, is scheduled to appear today in D.C. Superior Court.

He left the apartment after the shooting, and police looked for him until he turned himself in about 2:30 p.m. yesterday. According to police, he told detectives that he tossed the weapon into a field near the apartment building, but the gun has not been recovered.

Wood was charged in February with possessing and intending to distribute drugs after he was arrested by D.C. police with 57 small bags of marijuana, court records show. A D.C. Superior Court judge found him guilty in August and sentenced him to 18 months of probation.

Wood failed to show up for a meeting with his probation officer Sept. 13, authorities said after a preliminary review of the records. The Court Services and Offender Supervision Agency had been trying to locate him, officials said.

Wood's sister, who would not give her first name, said that her brother was sorry for the shooting but that he called it an accident. "I'm going to stand behind my brother," the sister said. "He's very sorry about what happened. . . . He's always been a good kid. He's not a murderer."

Yesterday, Richie T. Baylor, 17, who was inside the apartment at the time of the killing, said he and Michael were about to enjoy a cigar when the bullet struck his friend. "He was too young to go like that, over an accident," Baylor said.

Michael was skipping school because he was afraid of getting beaten by teenagers from a rival neighborhood, Baylor said.

The teenager's death pushed the number of juveniles killed in the District to 21 this year. Last year, 12 juveniles were slain.

Michael, who lived in the apartment complex where he was shot, had a history of skipping classes at Johnson Junior High School. His mother, Pamela Swann, said she had been working hard to keep the seventh-grader in class.

Yesterday, school officials said Johnson students were trying to cope with the death of a classmate. Principal Sylvia Dark said that she held two assemblies and that students were able to ask questions and talk with counselors.

"They asked general questions, like, "Why do people so young have to die?' " Dark said. "I told them . . . that even when doing the right things, making the right decisions, it doesn't always turn out right. It's just a fact of life. We don't know when or where."

Staff writer Henri E. Cauvin and staff researcher Bobbye Pratt contributed to this report.