The night he was arrested 17-year-old James Lewis Lathon of Fairfax County, told police he strangled his 15-year-old girlfriend in a jealous rage and then discarded her body in a gravel pit, covered by a cardboard box.

"I realized she had been out with another guy," said Lathon to Fairfax police. "She had hickies all over her neck and something just made me go off, and I killed her."

Yesterday, despite taking the stand to repudiate his earlier statement, Lathon was convicted by Fairfax County Circuit Judge Richard J. Jamborsky of second-degree murder in the strangulation death last September of Karen Benson, whose deteriorated body was discovered two months later in a gravel pit near the Springfield Mall. His sentencing was delayed until April 24.

According to a transcript of Lathon's confession, which was admitted as evidence over the objections of his attorneys, Lathon admitted strangling Benson with an Ace bandage in the bedroom of his brother's rented home in Groveton Sept. 24, two days after her 15th birthday.

On Dec. 10, the night he was arrested, Lathon told detectives that Benson "laughed" when he wrapped the bandage around her neck and that he did not mean to kill her. But when realized she was dead, he carried her body out to his brother's pickup truck.

According to police, Lathon said he put the partially clothed girl and some of her clothes into the cab of the truck, then drove to the gravel pit where he left her body, covered by the cardboard box.

When the body was found two months later by children playing in the pit, the box was still covering her.

"There were many things he told the police in the course of his confession that they had no idea existed," said Steven A. Merril, deputy commonwealth's attorney for Fairfax County, who prosecuted Lathon. "He was able to describe the scene and what he had done to her."

Defense attoreys Jason D. Smolen and Alan B. Plevy argued in a pretrial hearing last week that Lathon's statement had been coerced by detectives who told Lathon he would not be allowed to sleep until be confesed to the crime. Judge Jamborsky refused to strike the juvenile's statement. "Once that statement was allowed, there wasn't much we could do," said Smolen.

In a previous hearing, a judge had ruled that Lathon should stand trial as an adult because of the seriousness of the crime.