As police first told the story, a young gang member named Javier Francisco Ovando burst through the door of a run-down apartment here three years ago, brandishing an assault weapon at two members of an elite anti-gang force of Los Angeles police officers on a stakeout. Startled, the officers shouted "Police!" and ordered Ovando to drop his weapon, then opened fire.

Or so they said. Now, in a scandal roiling this city, one of the LAPD's own has told investigators that Ovando had no gun. That police shot him anyway and then planted a gun on him to make it look good. Then they framed him. Then they lied under oath and watched as an innocent man -- disabled and in a wheelchair as a result of their bullets -- was tried, convicted and sentenced to 23 years in prison.

Since the extraordinary allegations came to light a week ago, at least a dozen officers in gang-fighting squads have become targets of a widening corruption probe that Mayor Richard Riordan said is casting a "dark shadow" over the Los Angeles Police Department.

Police Chief Bernard Parks is assembling a 50-person investigative team charged with poring through old cases and interviewing officers and crime victims in hopes of uncovering the extent of the corruption.

"When you look at the depth and breadth of the [charges], certainly anyone who would not be horrified by some of these things is not human," Parks told reporters at a news conference.

The LAPD was just beginning to recover from a series of disastrous episodes earlier this decade -- the videotaped beating of Rodney King, the worst riots in U.S. history, and detective Mark Fuhrman's racism and perjury in the O.J. Simpson murder case. But this latest and still unfolding scandal is already one of the biggest in city history, and public confidence in the institution, and in those who oversee it, has been knocked on its heels.

The scandal also is the latest among many tales of trigger-happy tactics and dirty cops that in recent years have provoked community outrage across the country, from New York City to New Orleans to the District.

"This is a very delicate moment for the LAPD," said Merrick Bobb, a specialist in police reform who has investigated the LAPD and the Los Angeles County Sheriff's Department in the past. "Community confidence hangs in the balance."

So far, 11 LAPD officers have been relieved of duty pending the investigation and one has been fired. In addition, one officer was found guilty of robbing a bank and another of stealing eight pounds of cocaine from a department lockup.

In the wake of the revelations, Ovando was freed from prison last week after prosecutors concluded that police had lied under oath about the whole episode.

Finally, because the most damning testimony to secure "gang injunctions," a tough legal tool used to prohibit alleged gang members from associating with one another, came from officers now under suspicion, two of the injunctions have been suspended. The injunctions, along with the tough policing of gang members, have been heralded by city officials as their strongest weapons against gang-related violence.

The accusations of police corruption have struck a department that even its harshest critics say is a relatively well-run and professional force compared with a decade ago.

"The Rodney King incident cast a huge shadow over the department, and there have been a lot of commanders and officers who have been toiling to change its reputation," said Katherine Mader, the LAPD's first inspector general, who left her job earlier this year, frustrated that she did not have more power to investigate alleged police abuses. "Now, to have this happen, it's like finding out your brother is a child molester. It's horrific for the department."

The central allegations revolve around revelations provided by former LAPD officer Rafael A. Perez, who stole eight pounds of seized cocaine from a department locker and is providing information about police corruption in exchange for a lighter sentence.

Most of the charges involve the anti-gang CRASH unit operating in a neighborhood just west of downtown, known as the Rampart Division. CRASH stands for Community Resources Against Street Hoodlums.

This CRASH unit patrols one of the city's most dangerous crime districts, one filled with recent immigrants from Mexico and Central America and their children.

In 1996, Perez and other officers from the CRASH unit were staking out a house in the neighborhood, searching, they said, for a cache of stolen weapons. At the time, they claimed that an alleged member of the 18th Street gang, Javier Francisco Ovando, burst in on them brandishing a sawed-off assault rifle. Ovando was shot three times by the officers, who then testified against him in court.

Ovando was sentenced to 23 years in prison and will spend the rest of his life in a wheelchair. At his sentencing, the judge remarked that Ovando seemed to show no remorse for threatening to kill a couple of LAPD officers.

But according to police investigators and city prosecutors, Perez now admits the shooting was "dirty," that Ovando was shot by police and then had a gun put in his hands. Ovando had no criminal record.

"It is absolutely stunning," said Dennis Chang, a lawyer who represents Ovando's young daughter and is planning to sue the LAPD on the child's behalf. "They took a guy. They handcuffed him. They shot him in the head. They put a gun in his hand. They framed him. They lied in court and then they put him in a cage."

Chang also is angry that Ovando is being protected by a "security detail" of LAPD officers. LAPD officials say Ovando requested the protection. Chang asked, "Protected from who?"

Police investigators also are looking into another shooting that Perez reportedly has said is suspect. In this case, CRASH units were said to be attempting to stop a retaliatory shooting by gang members. In an ensuing shootout, one person was killed and two others were wounded. One of the wounded had been reported by police to be brandishing a gun and was shot in the chest. But in a jailhouse interview with the Los Angeles Times, Jose Perez showed two reporters bullet wounds on his back, not his chest.

Connie Rice, a civil rights lawyer who has sued the LAPD in the past, said she and others believe that authorities have helped to create a climate in which police officers feel confident in using excessive measures in pursuit of gang members.

As politicians and officials use rhetoric such as declaring "a war on gang violence," Rice said, "you tell the cops that they are warriors fighting a war, and in a war, you use the tactics of war."

Rice and other activists say it is common for CRASH unit officers to begin behaving a bit like gang members, getting tattoos, using hand signs, and adopting the macho posture of the streets and street slang.

The ongoing investigations and surrounding scandal are already shaking up the city's political culture, from Riordan to Parks to the city attorney, James Hahn, who is planning to run for mayor.

Even fans of Parks, who has a reputation as a strict disciplinarian, say that he has yet to win strong allegiances from some of the rank-and-file officers he needs most to help change the LAPD culture. Earlier this year, a group of officers announced that they were so dismayed with the chief's leadership that they did not even want him to attend their funerals if they were killed in the line of duty.