Prince George's County police have charged three people with first-degree murder in the shooting deaths of three young people Friday in Forestville, authorities said.

Marcus William Tunstall, 17, of the 10100 block of Scotch Hill Lane in Largo, was arrested late Monday on a weapon charge after an officer stopped him for a traffic violation and found a knife in his car, police said.

Tunstall was charged as an adult with first-degree murder after giving detectives a statement, police said.

Gordon Maurice Prailow, 19, who was implicated by Tunstall, was arrested a short time later at his home in the 4300 block of Shell Street in Capitol Heights, police said. Both were being held yesterday without bond at the Prince George's County jail.

George Anthony Thorne, 24, of the 4700 block of C Street SE, was arrested yesterday afternoon in Alexandria and was being held for an extradtion hearing.

Tunstall, Prailow and Thorne are charged in the deaths of Derick Sean Williams, 16, of Forestville; Michael Labrent Martin, 20, of Largo; and Stewart Alexander Smith, 17, of Forestville. Police sources characterized the killings as drug-related and said that they were committed during a robbery rampage that took the assailants from one apartment to the other Friday afternoon.

The sources also said that Tunstall and Prailow and the victims all knew each other.

Williams and Martin were found by Williams's mother about 4:30 p.m. Friday in the Williams's apartment in the Surrey Square complex in Forestville. Martin was pronounced dead at the scene; Williams was flown to Washington Hospital Center, where he died.

Three hours later, Smith's mother found him shot to death in a bedroom of their apartment in the nearby Park Berkshire complex in the 6400 block of Pennsylvania Avenue.

Police sources said that Smith was taken from Suitland High School to his apartment where he was robbed and then shot several times. Smith's assailants then went to Williams's apartment nearby also intending to rob him, the sources said. Martin, who was visiting Williams, also was shot, police said.