Larry Viscidi, a principal figure in one of the area's most celebrated recent police cases, buried his 12-year-old brother and concealed evidence of what he had done because the sight of his dead brother "was so horrible he didn't want anybody to see it," his father said his week.

Larry, 15, was recently cleared of involvement in the July 25 death of his brother Billy, whose body was found weeks later wrapped in a plastic trash bag and buried in the back yard of the family's Vienna home. Fairfax County Juvenile Court Judge Arnold B. Kassabian ruled in a closed trial on Jan. 19 that the evidence against Larry was circumstantial and insufficient for a conviction.

Almost a month after Billy's decomposed body was found Aug. 12, Larry admitted to police that he buried his brother's body, but would never say why, a source familiar with the investigation said.

Burton Viscidi, the boys' father, said this week the youth buried Billy because he didn't want his parents to see "something so horrible... Billy with his head split open... So he buried the body and went to sleep.

"It was just so horrible, he couldn't face it... He had amnesia, he blocked it out," the elder Viscidi said in an interview as Larry sat silent on the living room couch.

That, he continued, explains why Larry kept silent for weeks while police and citizens launched an intensive hunt for Billy. It was only after a psychologist subjected Larry to 20 hours of hypnosis and a psychiatrist administered truth serum, his father said, that Larry's memories of what transpired were revived.

Burton Viscidi's comments came as he and his wife, Grace, broke a months-long, self-imposed silence about the case.

The couple consented to a television interview with a WRC reporter on Sunday after Grace Viscidi first contacted the reporter by telephone during a radio talk show.

During the televised interview. Grace Viscidi said that "two separate, horrible things have happened to us. Losing Billy was the worst, because Larry's problem we can work with. There is nothing we can do about Billy."

In a separate interview with a reporter this week, the Viscidis have revealed details and their own theories about their son's baffling death. They also have criticized Fairfax County police, the press and prosecutors for their handling of the case.

The family's principal theory of Billy's death, according to Burton Viscidi, is that on the morning of July 25, Larry Viscidi was in the family basement fixing his bicycle when he had a sudden nosebleed. Neither of his parents was at home at the time.

As he started up the stairs to treat the nosebleed, he heard running and a loud thump. When he got to the living room, he found his brother lying on the floor, dead from a massive head wound. According to the elder Viscidi. Billy could have died because he ran, tripped and fell near the family's living-room bookcase.

The prosecution's case, as argued in closed-door hearings by Fairfax Commonwealth's Attorney Robert F. Horan Jr., was quite different, sources, said. Horan contended during the trial that in the course of a fight between the two boys, Larry seized a five-pound onyx elephant resting on a nearby shelf and hit Billy on the back of the head with it.

That argument, sources said, rested in part on the statement of Fairfax County Medical Examiner James C. Byer that Billy died from a skull fracture that could have been caused by a blow inflicted with considerable force.

Byer also testified that a fall from a tree, out of a house or down stairs could have produced a similar skull fracture. But under cross-examination, the medical expert conceded that a running fall of considerable force might also have produced the fracture, sources said.

Another medical expert, the District's chief deputy medical examiner, Brian D. Blackbourne, told the court that in his opinion, Billy did not die from a fall or "running into a wall."

"He would have to have been doubled-over forward, which would have been a very awkward position," Blackbourne told a reporter last week.

Additional details of what happened that summer morning were provided in court by a neighborhood youngster. According to sources, the girl testified that during a visit to the Viscidi home she watched while Larry scrubbed and vacuumed a bloody area of the living-room carpet and cleaned numerous blood spots off a bathroom wall.

Larry told the youngster that his nosebleed caused the bloodspots, although she testified that she never saw any evidence of nosebleed. Then Larry told her not to tell anyone of his cleaning, according to her testimony.

Grace Viscidi told a reporter yesterday that Larry has nosebleeds frequently, "although when he was younger, it was worse."

Burton Viscidi said this week that Larry cleaned up after the body, placing his own "bloody" clothes in the trash bag along with Billy's body, so "nobody would see what he had just seen."

When police examined the contents of the bag, they found numerous articles of clothing, some blood-stained and some identified later as belonging to Larry. Included among other things were Larry's cut-off denims, jockey shorts and a T-shirt it was learned.

In this week's interviews, Burton and Grace Viscidi said they believe that their treatment by authorities and the press has been unfair.

"We are angry about what has happened with the press and the police. The pressure was on them to make an arrest. Larry was the sacrificial lamb," Burton Viscidi said.

Prosecutor Horan yesterday rejected that contention. "There was no sacrificial lamb in the case," he said.

Under the evidence, Horan said, "police not only had a right but a duty" to arrest Larry. And, he added, if the Viscidi family were willing to permit disclosure in te still-secret case, "I would be delighted to advise the press of what evidence we had in the case of Billy Viscidi. I would be delighted to have anyone look at that evidence."

Horan added yesterday that some of the theories being advanced by the Viscidis of how Billy died -- "pretty good theories," according to Burton Viscidi -- are inconsistent with the evidence and refuted by the medical testimony in the case.

The possibility that a blood clot caused by a weeks-old car accident killed Billy or that the onyx elephant tumbled off a shelf and caused the massive head would were both contradicted by the testimony of the medical experts, Horan said.

"Dr. Blackbourne testified that there was no possibility of a blood clot or a hairline fracture... Blackbourne went into great detail and rejected it. Blackbourne also testified regarding the "elephant" theory, Horan said, "and rejected it."

Burton Viscidi also said it is possible that someone entered through the Viscidis' unlocked front doors and killed the boy. Horan said yesterday there is not "a chance in the world that could have occurred."