John J. Wiley's memory returns to the frigid December night four years ago when his life fell apart.

Once again he wears the navy uniform of a Baltimore cop. And once again, he stands in the mouth of a narrow alley, his heart pounding, his eyes searching. In one hand, he holds a gun; in the other a flashlight, flicking its beam from side to side. He sees nothing. He hears only the crackling of the radio on his shoulder. Finally, he returns the puddle of light to the ground and the young man who lies gasping and bleeding and dying before him.

What had happened in the preceding moments defines John Wiley.

They render him either a killer, a liar, or an innocent, living casualty of that death and its aftermath. He either fired a shot into the back of John Randolph Scott, a suspected car thief pursued by more than two dozen cops, he covered up for the police officer who did, or he had the misfortune of being first on the scene after the shooting.

Which role he played remains a riddle to city homicide investigators. That continuing mystery, John Wiley says, has been his curse. Others may say it is his protection from prison.

Indisputably, though, Mr. Scott's death is the demarcation in John Wiley's 33 years. Before, he was strong and cocky, full of promise and possibility. After, he was scared and despairing, his career destroyed, his thoughts untrustworthy.

Before, he was "one of the good guys," decorated and promoted for valor. After, when the taint was on him, he did not know what he was.

He was never charged with murder or anything else, but neither has he ever been exonerated or Mr. Scott's death solved.

"I have this thing over my head, and I can't get rid of it," he laments, drawing on his cigarette, his eyes bloodshot.

Under the pressure of suspicion, he crumbled. Twice in the past six months he tried to kill himself, once with a gun, once with a razor blade. "Sometimes, I've gone to put my gun away and suddenly the urge to kill myself would be right there like that," he says, snapping his fingers.

In the dying light of an autumn afternoon, he sits in his living room in Southern Maryland, where he has escaped with his wife and their two young daughters. His eyes are moist, the hand holding his cigarette unsteady. Your instinct is to sympathize, but something stops you. What is the true source of his anguish? A wrongful accusation or a guilty conscience?

If John Wiley -- Jay to his family and friends -- had pursued hiyouthful ambition to become a priest, he would have been an imposing figure in the pulpit. His hair is curly blond, his body muscular. His booming voice would have resonated in the back pews. By his junior year in his Virginia high school, though, he knew the priesthood was not in his future. "Girls," he explained.

He began thinking about becoming a cop then. The image appealed to his black-and-white sense of the world. "It made perfect sense to go from wanting to be a priest to a cop," he said. "I wanted to help people. I always had intolerance for anyone abusing people smaller or weaker than they were."

In 1980, at age 21, he spotted a Baltimore billboard soliciting police recruits.

Two weeks later, he was issued the khaki uniform of a Baltimore police cadet. The following spring, he traded in khaki for blue, and began patrolling the streets of Northwest Baltimore.

"I knew right away"

"I loved it," he says now. "I knew right away that this is what I wanted to be. I used to joke that I was going to be a captain or a major within 20 years. I expected to be doing this for the next 30 years."

The Northwest was a rough training ground. "You had to get smart quick," he said. "You had to learn fast who were the good guys and who were the bad guys. If you were going to survive, you had to learn not to go around like you were the baddest guy on the block. You can't fight every day."

He learned to be tough and shrewd, and excelled at his job. He received 11 awards, including two bronze stars, one silver star and a commendatory letter from the police commissioner.

He gravitated to narcotics undercover, and in 1986 was assigned to a drug task force investigating Jamaican traffickers in Northwest Baltimore.

"He was a great cop," said Katharine Armentrout, now head of the organized crime drug task force unit for the U.S. attorney's office. She said he often worked dangerous surveillance and arrests and never lost his head.

"I don't like cowboy cops," she said. "I know cowboy cops when I see one and I saw nothing that indicated he was one. . . . We need good cops and he was a great cop."

In September 1987, he was promoted to sergeant at age 28. He was sent to the Central District, where his aggressiveness quickly established him as a favorite.

"The younger cops thought he was God," said Officer Charles Bealefeld, who worked under Sergeant Wiley. "With him it was like 'Screw the paperwork. Let's get out there and kick ass and take names.' That's my impression of a good cop."

Officer Bealefeld said Sergeant Wiley's behavior stirred resentment among older cops. Sergeant Wiley knew other sergeants thought his presence on the streets was unseemly. "But my attitude was, 'How can I ask these guys to do things if they don't know I can do it?' "

Three months later, that attitude deposited him in an alley on North Monroe Street.

"A bad night"

John Wiley's life began to unravel about 2:15 on a clear, biting morning when two Baltimore patrol cars began chasing a stolen car, a dark red Dodge Colt, into West Baltimore. The Dodge's driver was 21-year-old Christopher Dinkins; the passenger, John Randolph Scott, 22.

Mr. Dinkins swerved the Dodge onto a side street. Both men bailed out of the car and split up. Officer Brian Pedrick leapt out of his car and raced after Mr. Scott.

Meanwhile, police radio broadcasts were drawing more than two dozen other cops to the vicinity of the chase.

As Officer Pedrick sped after Mr. Scott, he stumbled and the gun in his hand discharged. Mr. Scott kept running and disappeared.

According to his later account, Sergeant Wiley had been on Mount Royal Avenue talking to another officer when the radio alerted him to the chase. He drove off to help.

Heading west on Lafayette Avenue, he said he was approaching Monroe Street when he heard a loud noise through his open window.

"I thought I had driven into an unrelated gunbattle." He turned north on Monroe, swiveling his head from side to side.

In an alley to his right, he immediately spotted a body.

"I pulled into the alley and got out of the car with my revolver and flashlight. I checked the kid to make sure he had no gun. Then I looked up the alley. There was no one. I reholstered the gun and went back to the body. I could tell he was dying. He was getting thick blood from his mouth and ear."

Other officers and an ambulance crew arrived. Within minutes, Mr. Scott, his heart torn apart, was dead. An ashen-faced Officer Pedrick told Sergeant Wiley about his gun discharging. "I went on [the radio] and said, 'Police-involved shooting,' " Sergeant Wiley said. He collected Officer Pedrick's service revolver, holster and gun belt.

"What are you telling me?"

When his shift ended, Sergeant Wiley went home. He was distraught about witnessing a man die, he said. He felt sorry for Officer Pedrick. It had been a bad night, but that wasn't unusual on this job.

Two days later, John Randolph Scott's death was a full-blown mystery.

By then, homicide detectives knew the bullet that had killed Mr. Scott had not come from Officer Pedrick's service revolver. They found the slug from his gun in the alley where he had tripped.

The case was politically sensitive, too. An accidental police shooting would have been bad enough. Now, the police department had a black fugitive shot in the back just as more than two dozen cops were closing in on him.

Attention shifted to John Wiley. He was summoned to the Homicide Unit, where detectives ordered him to turn in his service revolver and his off-duty gun for ballistics tests.

"I was like somebody struck stupid," Sergeant Wiley recalled. "I looked at them like, 'What are you telling me?' "

It soon became clear. He was a suspect. A seven-year veteran then, he had arrested countless murder suspects. Now, he would find himself the object of interrogations, searches of his home, lie detector tests and subpoenas.

The homicide detectives who conducted the investigation declined to be interviewed for this article. Police Department officials and Timothy Doory, who handled the case for the Baltimore state's attorney's office, also declined to comment.

From the start, the detectives were hampered by a frustrating lack of evidence. The revolvers of more than 30 cops were collected and tested. None matched the bullet that killed Mr. Scott.

There were no witnesses to the Dec. 7, 1987, shooting, although one resident reported seeing a police car driving from the alley moments after the gunshot. Seconds later, he said he saw an officer, presumably Sergeant Wiley, leave his parked patrol car and walk into the alley.

"Cancel that description"

There was little to link Sergeant Wiley to the shooting. The tests on his two guns were negative. His uniform, gun belt, jacket and shoes did not produce gunpowder residue that would have demonstrated the recent firing of a gun.

But his polygraph was inconclusive. (Police union lawyers are suing the Police Department and prosecutor's office for forcing Sergeant Wiley and three other officers to take the lie-detector tests.)

And two sentences in his radio transmissions nagged at the detectives.

Nearly four minutes after Mr. Scott jumped from the Dodge, a cop, apparently Officer Pedrick, broadcast a description of Mr. Scott.

Sergeant Wiley's voice then came over the radio. "Cancel that description at the 800 block of Fulton . . . or Monroe," he said, a signal that he had apprehended the man.

Officer Pedrick radioed, "I can ID that guy."

A few seconds later, Seargeant Wiley transmitted another message. "I got a possible gunshot here right before I found this guy," he said.

In their interrogations of Sergeant Wiley, the detectives again and again returned to those transmissions.

They told him that his "Cancel the description" seemed an unlikely thing to say after discovering a body. And his later report of hearing a gunshot seemed an afterthought, perhaps an attempt to correct the record.

Sergeant Wiley protested that he sent two earlier messages, one reporting the gunshot and the other his discovery of a body. A tape recording from that night, however, revealed no such transmissions.

Sergeant Wiley insisted that he must have failed to hit the transmit button or had been overridden by another transmission, a frequent event.

He said he never noticed that the dispatcher hadn't acknowledged his statements.

"I was afraid the shooter was still in the alley," he said. "I wasn't paying attention to the radio, but no matter what I said, I couldn't make them believe me."

The detectives formed a theory, according to several officers who were also interrogated. Seargeant Wiley caught Mr. Scott in the alley. The two men struggled, which explained why buttons from Mr. Scott's shirt were found on the ground. Mr. Scott pulled a gun. Sergeant Wiley got it from him. They broke apart, and Sergeant Wiley fired the gun. Before any other officers arrived, he hid the weapon, which he later disposed of.

"I didn't kill John Scott"

"I'm not going to sit here and tell you it can't happen that way," Sergeant Wiley said of the detectives' version. "It didn't."

Butressing his denial was Mr. Dinkins' later insistence that neither he nor Mr. Scott had a gun that night.

Sergeant Wiley said it was just as likely that Mr. Scott chanced upon a drug buy in the alley and was shot by a jittery dealer. It's also possible that another police officer killed Mr. Scott, he said.

A few months after the shooting, Sergeant Wiley was summoned to Mr. Doory's office. In front of Henry L. Belsky, a union lawyer representing Sergeant Wiley, Mr. Doory offered the officer immunity from prosecution if he would confess. Mr. Doory

accused Sergeant Wiley of panicking after the shooting and then lying about it, or covering up for another cop. "He said once I made the mistake of lying about it I had gone so far that I couldn't come back."

Sergeant Wiley exploded. "I didn't kill John Scott and I don't know who did," he bellowed. "Immunity is for Mafioso or politicians. I'm neither."

In May 1988, Sergeant Wiley was called before a grand jury. Mr. Belsky urged his client to plead the Fifth Amendment.

"People, and especially cops, have this misconception that by testifying, you exonerate yourself," Mr. Belsky said. "That's not true, when you testify, you put yourself in it. They'll use any inconsistency in your statement to indict you. Why should you help them?"

Sergeant Wiley objected. "I told him if I take the Fifth, I'm going to look like a drug dealer, a common criminal," Sergeant Wiley recalled. "I'm a cop. I'm a good guy."

But Mr. Belsky was uncompromising. Sergeant Wiley appeared before the grand jury, and he took the Fifth. He cried all the way home.

"I just wanted to stop"

He vowed not to let it show, the fear, the shame. He didn't want his wife, Anne, pregnant with their first child, to see his anxiety. He sure as hell didn't want the detectives see it either and conclude he "was acting guilty. I wasn't going to let them see me flinch," he said. "I was going to go out and be a much better cop than anyone else and show it wasn't affecting me."

But he couldn't carry it off. Mrs. Wiley saw the changes in her husband from the start. Normally outgoing and effusive, now he was distant and quiet. He was drinking to put himself to sleep at night. Often he awakened from nightmares.

His fellow cops noticed as well. His intensity and zeal on the job frightened Officer Bealefeld so much that he requested a transfer. Old friends on the force felt that he had virtually cut them off.

The humiliation, he said, was unbearable. One day, he went to work and found blue evidence tape wrapped around his patrol car, trumpeting to his fellow officers the suspicions about him. The Central District started a pool to pick the day he would be jailed.

To Sergeant Wiley, the world had only included good guys and bad guys, and he always knew where he stood. Now he found himself in a moral limbo, neither innocent nor guilty. "Never did I have to question my own thoughts about who I am or what I was capable of," he said. "Now, I don't even have a clue."

He expected to be charged with murder. "I spent every day thinking I was going to be arrested. Every time I got a call to come back to the station, I thought this was going to be it."

At Mrs. Wiley's urging, he started seeing a psychologist, but his moods only worsened. He blew up at Mrs. Wiley over nothing, sometimes throwing dishes or punching the refrigerator. Once or twice, he said, he nearly struck his wife.

One night she opened their front door to find her husband sobbing, his shoulders shaking. "I'd never seen him that way," she recalled. "He said, 'Anne you can't believe what they're doing to me. I just want it to stop. I just want it to stop.' "

Even after the grand jury did not return an indictment against him, he felt no relief. "Everyone was telling me I had to put it behind me and get on with my life," he said. "But I couldn't. I couldn't."

"You're famous now"

Hoping a return to familiar territory would help, he transferred back to the Northwest District in 1989. In the next year, though, he was shot at twice. Both incidents left him badly shaken and injured from struggling with the men he was trying to arrest.

Soon after those episodes, he learned of two threats made against him by drug dealers. Sometimes, Sergeant Wiley worried the threats had come from the Police Department.

His fears were intensifying. He believed his phone was tapped. He believed he was being followed. He refused to be without a gun at any time. He slept with one on the night table and carried one from room to room in his house.

In the summer of 1990, he insisted on moving to Southern Maryland. (He asked that the exact location be withheld in this article.) His wife reluctantly agreed. "I hate it down here," said Mrs. Wiley, who works as an emergency room nurse. "But everything in Baltimore seemed to remind him of the shooting. At least here, he might be able to get away from it for a while."

In January, still bothered by injuries he had sustained on the job, he went on medical leave. He has now applied for a disability pension because of both the injuries and the emotional distress of the homicide investigation. The case is pending.

Absence from the department eased his anxiety, until one day last spring when he was visiting the Police Department. "Hey, Wiley," someone said to him. "You're famous now."

The man explained that a book about the Baltimore homicide unit had just been published. Sergeant Wiley was in it. The book, "Homicide" by Baltimore Sun reporter David Simon, was written from the perspective of the homicide detectives and included an account of the Scott killing. It related all the suspicions about Sergeant Wiley.

The book plunged him into the deepest despair yet. "He was consumed by it," Mrs. Wiley said. "It was all he could talk about. I'd get home at 12:30 or 1, and he'd be there talking about it. When I got up in the morning, it was the only thing on his mind."

To the list of detectives and prosecutors who had wronged him, Sergeant Wiley added Mr. Simon. He began harboring "assaultive thoughts" against him as well as the detectives and Mr. Doory. He stopped eating or he ate in binges. He wouldn't leave his house or dress during the day. And he flew into rages against Mrs. Wiley.

They separated briefly, but when Sergeant Wiley returned home, he was no better.

In late July when his family was away, he spent yet another night drinking himself into drowsiness. "I grabbed my 9mm off the refrigerator to go to bed," he said, "and I started to put the gun in my mouth. The thought suddenly came up to end all this. I stood there two or three minutes debating whether to kill myself."

Thoughts of his children pulled him back. "If I'd been single," he said, "I would have killed myself a long time ago."

"I want to be exonerated"

Several days later, he checked into a New York psychiatric hospital for a monthlong stay. He was diagnosed as suffering from major depression and post-traumatic stress syndrome. Psychological evaluations described him as "non-functional" and "totally incapacitated from an emotional point of view." One report said he was "increasingly suspicious and paranoid and has been experiencing flashbacks of particular violent episodes from his time with the Police Department."

Three weeks after leaving the hospital, he stood for an hour on the balcony of his house trying to slice his wrists with a razor blade. That attempt led to his hospitalization at Sheppard Pratt. But, with his health insurance running out, he couldn't afford to stay longer than a week. Now he is relying on therapy sessions and medication.

He views the last four years as lost -- his career over, his family life sacrificed to the torment he cannot escape. Knowing how fragile he is, Mrs. Wiley dares not even discuss the future with him.

Sergeant Wiley wants a declaration that he was an innocent man, a damned good cop whose only mistake was rushing to do his job. He wants to be restored as one of the good guys. "I want to be exonerated," he said.

His attorney, Mr. Belsky, says it is a reasonable request. It also won't happen. "I think there should be some finality to these things," Mr. Belsky said. "The truth of the matter is that unless something pops up, it's a dead case. But they're never going to take Wiley off the hook, and he's always going to be waiting for someone to knock on his door."

Mrs. Wiley said she has given up hope for a resolution. "I don't expect anything from anyone," she said. "I'm prepared to live the rest of our lives with this hanging over us. I'm not sure I can say that for Jay."