A 15-year-old boy who died six months ago shortly after being found unconscious in his family's apartment in Southeast Washington was beaten to death, authorities announced yesterday.

Sherrod J. Miller, a sophomore at Ballou Senior High School who was known by friends as "the Gentle Giant," is among 18 juveniles to be killed in the District this year, six more than all of last year. No suspects have been arrested in Miller's death.

The teenager was found unconscious early March 19 on the floor of his family's apartment in the 1300 block of Congress Street SE, police said. He was pronounced dead that day at Greater Southeast Medical Center. Soon after the death, police officials said that Miller's body was heavily bruised. Family members said they also learned that he had a heart condition.

The medical examiner ruled Tuesday that Miller's heart stopped after he was badly beaten, police said.

Anna Francis, spokeswoman for the D.C. medical examiner's office, said it took six months to determine how Miller died because the case "was a complicated one." She said pathologists had to wait for results of additional tests before making their ruling.

Lt. Lamar Greene of the police department's violent crimes unit said detectives have treated the death as a homicide from the moment relatives discovered Miller's body. Greene declined to say whether investigators had any suspects.

"We have interviewed a lot of people," Greene said.

Miller's godmother and guardian, Charlotte Green, described him last spring as a good student and athlete. He played basketball and football at Ballou, school officials said.

Miller is among three Ballou students slain this year. James Richardson, 17, was shot to death inside the Southeast school in February. Timothy Hamilton, a 15-year-old freshman, was shot to death in April in Southeast.