The sun's rays danced on John Sealock's slightly balding head one day last week as the Loudoun County deputy walked the brick-lined streets of Leesburg, smiling and waving at passing motorists, who honked in recognition.

A lot of county residents know John Sealock, a soft-spoken, unassuming man of 40 who has been with the Loudoun sheriff's department for 14 years. Sealock, a captain in the Andy Griffith/Andy Taylor mold, believes in being friendly, and he is as likely to start a conversation with a stranger as he is with a longtime buddy.

Thus it was that, 11 or 12 years ago, Sealock came to know Charles Curtis, an acquaintance that provided a turning point in one of Loudoun County's most baffling and well-publicized slayings -- that of Judith L. DeMaria.

DeMaria, a 27-year-old tennis instructor at a Sterling fitness club, went for a midday jog on Aug. 2, 1985. She never came back, and until this month Loudoun deputies had been stymied in their investigation of her disappearance.

On Thursday, Curtis will have a preliminary hearing in Leesburg to determine if there is enough evidence to bind him over to a grand jury on a charge of first-degree murder.

"Chuckie and I go back a long way," Sealock said in an interview last week. "I met Chuck when he was . . . oh, 15 or 16 years old."

That was the mid-1970s, and Sealock was a rookie field deputy patrolling the Sterling section of eastern Loudoun County.

"I would see him and we would just talk, not about anything in particular, but things like hunting," Sealock said.

When Curtis, whom authorities describe as a drifter who passed through Loudoun at various times, was in the county jail in 1978 on breaking-and-entering and grand larceny charges, Sealock said he continued to chat with him.

And later, after Curtis completed a prison sentence, they renewed their acquaintance.

"He met these men in the state penitentiary, and they were describing how they were trying to kill me during a high-speed chase," Sealock said. "He said, 'That really had to be something.' That case fascinated him. He brings it up all the time."

An odd camaraderie formed between the two men.

"One time I saw him in Purcellville and . . . he introduced me to his girlfriend," Sealock said. "We shook hands and stood around and talked a few minutes."

But Sealock could hardly have imagined the conversation that he and Curtis, now 27, would have on Sept. 9 of this year.

Sealock was at the Dulles Holiday Inn with Sheriff John Isom that night to attend a lecture on terrorism when he got a call from the department dispatcher.

"I called the sergeant and he said there was a gentleman who wanted to talk about the DeMaria case {and} that he would only talk to me," Sealock said.

Sealock said he told the dispatcher that " 'I'd sure like to listen to this speaker,' {but} the sheriff said to go on over. On the DeMaria case, we followed every lead."

Sealock said that he and Curtis had never before discussed the celebrated case, and he declined to tell a reporter what Curtis told him that night.

But within hours of their conversation, local and federal authorities located badly decomposed remains of a body in a shallow grave near a bicycle path near Dulles International Airport, where DeMaria was last seen. An autopsy confirmed her identity, and Curtis was charged with murder.

Sealock said he believes Curtis sought him out because Curtis had respect for him as a police officer.

"It all boils down to how you treat people," said Sealock, who initially declined an interview, saying he did not want to overshadow the work of investigators Jay Merchant and Robert Turner, who have spent more than two years on the DeMaria case and whose work is crucial to it.

"How you treat people determines how they respond to you," he said.