An Oakton teenager admitted yesterday that he shot his parents to death in the basement of their home in February, pleading guilty to two counts of first-degree murder in Fairfax County Circuit Court.

Joshua P. Cooke's attorneys attracted attention this spring by filing a motion saying their client may not have known the difference between right and wrong because he "harbored a bona fide belief that he was living in the virtual reality of 'The Matrix,' " referring to the 1999 science fiction movie.

But Rachel M. Fierro, one of Cooke's court-appointed attorneys, said the psychiatric report they requested was not an issue "because Josh decided to accept responsibility for his actions and plead guilty."

Prosecutors revealed yesterday that Cooke's adoptive father, Paul C. Cooke, 51, was talking on the telephone with his teenage daughter, Tiffany M. Cooke, the night of Feb. 17 when Joshua Cooke, 19, went down to the basement of the family home in the 10500 block of Adel Road.

"She thought she heard her mother say, 'Josh, you wouldn't,' " Commonwealth's Attorney Robert F. Horan Jr. said.

"She then heard what she called popping sounds," Horan said. "A number of popping sounds, and the phone dropped."

Police believe Joshua Cooke shot his mother first. Margaret Ruffin Cooke's body was found at the foot of the basement stairs. An autopsy showed that the 56-year-old woman was shot twice.

Tiffany Cooke, 19, continued to listen. "She said it sounded like pans falling to the ground," Horan said.

An autopsy showed that Paul Cooke had been shot seven times. All nine shots were fired from a 12-gauge shotgun Joshua Cooke purchased two days earlier at the Galyan's sporting goods store in Fair Lakes.

Joshua Cooke then picked up the dangling phone, Horan said. " 'Josh, what are you doing? Let me talk to Daddy,' " Tiffany Cooke pleaded, according to Horan.

" 'I have to call somebody,' " Joshua Cooke told his sister, and he hung up the phone.

Police tapes then recorded Joshua Cooke twice calling the Fairfax 911 lines to report: "I just shot my parents. I just blew them away with a shotgun."

Cooke did not speak during the brief hearing before Fairfax County Circuit Court Judge Kathleen H. MacKay. But he will get an opportunity to do so at his sentencing hearing Aug. 7, for which his attorneys requested a full day to present evidence of Cooke's circumstances at the time of the killings.

Fierro said the movie would come up then. "There will be elements of 'The Matrix' theory in the sentencing hearing, regarding the influence of violent films and violent video games, as one of the factors in the murders," she said. She declined to elaborate.

Fierro said the sentencing hearing also may include evidence of "possible abuse by foster parents prior to being adopted by the Cookes, as well as emotional and physical abuse by the Cookes." She did not provide specifics.

Fierro said she could not say why Cooke shot his parents, who adopted him in 1991. "It's a combination of a lot of different factors," she said.

In addition to the two murder charges, Joshua Cooke also pleaded guilty to two counts of using a firearm in a felony, which could add nine years to any sentence he receives.

As part of a plea deal, prosecutors agreed not to ask MacKay to impose a sentence beyond the state sentencing guidelines, which are not mandatory. Horan said the guidelines call for a sentence of 28 to 50 years in prison on each count, which can run consecutively or concurrently.

Philip Terzian, who lives across the street from the Cookes and saw Joshua Cooke in handcuffs the night of the killings, attended the hearing, in which Horan replayed the tapes of Cooke's calm phone calls to dispatchers.

"It was surreal and unpleasant to listen to the details, knowing it was happening just a few yards away from you," Terzian said. The Cookes' home alarm system could be heard screeching in the background as Joshua Cooke spoke to a dispatcher, a reminder to Terzian of the eerie sound that snowy night.

"The only explanation I can conjure up," Terzian said, "is it was a virtual suicide and he didn't quite conclude it."