ON THE SECOND FLOOR OF THE LOS ANGELES County Jail sits a special, 90-inmate section commonly called "7,000." Also known as "High Power," the section is the jail's celebrity wing, the protective-custody unit where professional athletes, movie stars and television actors end up when they are accused of crimes and can't make bail. Otherwise ordinary defendants in highly publicized cases are imprisoned there, too: Raymond Buckey, for one, spent five long years in 7,000, waiting his eventual acquittal in the infamous McMartin Pre-School case. This combination of inmate types is made even more peculiar by the third class of prisoners relegated to High Power: police officers. Cops accused of crimes are housed here, isolated from the majority of inmates, who tend to view policemen in their midst with something less than enthusiasm. * Former Los Angeles Police Officer William Earnest Leasure is the elder statesman of the 7,000 block--he has lived here longer than any other inmate. He has seen most of the big names come and go: the Night Stalker, the "Cheers" co-star in for drug possession, the former regular on "Bonanza" accused of dealing coke, even Charles Keating. But Leasure has hardly seen the sun in five years. The brief exercise periods on the jail roof for the residents of 7,000 come only at night, three times a week, when no other inmates are around. After five years in custody, Leasure has all the color of a mushroom. * Gone, too, is the confident stride of an LAPD officer. Now Leasure walks and sits with a jailhouse hunch, the round-shouldered slouch long-timers invariably develop. Once you've been in long enough, you rate the coveted bottom bunk in your cell--but the trade-off is, you develop chronic poor posture to avoid banging your head against the upper berth. Leasure's got it bad: He looks shorter than 5-foot-10, as if the weight of all the restraining concrete and steel bars around him is slowly compacting him. During visits, his mother repeatedly reminds her son to sit up straight. It's embarrassing for a man a few months shy of his 45th birthday, but he smiles and nods his balding head and says, "OK, mom," and tries to comply. Later, alone and stretched out on his narrow bottom bunk, he dreams of eating good pizza or maybe a decent hamburger, of flying one of his airplanes or driving fast in one of his beloved Corvettes . . . or of sitting up straight, his face to the sun. * Tucked under his bunk, he says, is his ticket to freedom: a row of eight cardboard file boxes, each one crammed with police reports, interrogation summaries and transcripts of witness interviews and surveillance tapes. This is the "discovery" in his case--copies of the state's voluminous evidence in the People vs. William Leasure. LAPD homicide detectives say the contents of these boxes prove that quiet, unassuming Traffic Officer William Leasure orchestrated two murders for hire and participated in a third--each of them carefully planned professional hits. * The boxed files also detail accusations that Leasure spent 10 of his 17 years in the LAPD leading a remarkable double life, writing tickets and working auto accidents by day, then spending his off-hours stealing a string of luxury yachts worth $2 million, trafficking in stolen cars and defrauding insurance companies. Investigators allege he had a lavish lifestyle without arousing the suspicions of his fellow officers--even as he boasted of secret bank accounts in the Cayman Islands, spoke of plans to buy a private Central American island and took his police friends out fishing and diving aboard his 42-foot, twin-engine yacht, Thunderbolt. * Leasure denies it all--he says he is being framed for the crimes, and maintains his lifestyle was well within the combined $110,000 annual earnings of a traffic cop and his higher-salaried wife, a senior assistant city attorney at the time of his arrest. In his six-man cell, he obsessively reads and re-reads the discovery files, making entries in a bulging diary, scrawling notes to Richard Lasting and Michael White, his court-appointed lawyers, and penciling long, neatly printed letters to the judge hearing his case, accusing the district attorney's office of withholding crucial evidence and covering up police misconduct. For the past five years, he has pored over these files, certain he can use the state's own case to disprove the charges against him. "It's all there. All you have to do is look at the evidence--their evidence," Leasure says, his hazel eyes bright behind metal-rimmed glasses, his voice patient and reasoned. "If you look at everything, I don't see how any reasonable person could not see the truth. And the truth is, I'm innocent. "I'm the nicest, quietest, mildest guy you'll ever want to meet," he says. "I've never killed anyone. I'd never hurt a fly."