A Manassas man was convicted yesterday in Fairfax County Circuit Court of first-degree murder and rape in the suffocation of a 15-year-old Chantilly girl who died while the two were having sex at a playground.

After about four hours of deliberation, a jury found Preston C. Brown, 22, guilty, and recommended sentences of life in prison for the murder and 50 years for rape. Brown is set to be sentenced Dec. 14.

Brown was arrested Aug. 6, one day after the body of Rebecca Lynette Reese was found behind town houses in the 4000 block of Mason Dixon Drive in Chantilly. Reese's body, naked from the waist down and clad only in a black T-shirt, a bra and a collar, was propped against a chain-link fence. According to an autopsy, the girl's face was swollen and bruised, and there were scrapes on her body.

In a tape-recorded statement played for the jury, Brown told police he and Reese had been hanging out at a playground when they began kissing. They moved to a more secluded area near a jungle gym and began to have sexual intercourse. At some point Reese changed her mind.

"She said we got to stop. We got to stop. We shouldn't be doing this. I said just a little bit longer," Brown said on the tape and began sobbing.

Commonwealth's Attorney Robert F. Horan Jr. said Brown then pushed her back down, pressing on her neck. She gagged and choked, he said.

"He is above her, pressing her toward the ground, closing off her ability to breathe. This large, 21-year-old man on top of a 5-foot-6, 128-pound, 15-year-old girl. He shuts off her life by closing off her ability to breathe," Horan told the jury during closing arguments.

"This defendant deprived that child of her most charitable right, the right to live at age 15. She lost it at his hands. She lost it because of his sexual demands. She lost it because of his lust."

Brown's attorney, William Reichhardt, told the jury the killing was not deliberate and happened during consensual intercourse.

Reichhardt read from Brown's statement, "I didn't mean to do it, I was just holding her down. I didn't mean to choke her. We were just having intercourse. I was just holding her down. It just happened so fast."

Horan argued that Reese had been beaten, and marks revealed that she had been restrained.

Reichhardt said that there was no evidence of a beating, therefore no evidence of force, and that the marks on the girl came from Brown's dragging her body 100 yards to hide it.

"They were laughing, giggling and making out," Reichhardt said. The prosecutor "wants you to believe all of a sudden he turns into a monster, a killer, a rapist, a kidnapper."