On a brisk January morning in 2007, seven New Orleans police officers waded through a crowd of cheering supporters outside the city's jail to face charges stemming from a deadly encounter with residents on a bridge in Hurricane Katrina's aftermath. Before they were booked, the grim-faced officers accepted hugs and handshakes from fellow cops who shouted, "Heroes! Heroes!"

Three of the officers who received the hero's welcome have admitted they were concealing a dark secret the day they surrendered, one so lurid it stunned a city with a long history of police corruption.

The other four members of the so-called Danziger Seven — named after the bridge where police shot and killed two unarmed people and wounded four others — and another police investigator go on trial Wednesday in a federal case that will rehash the most infamous chapter in the city's awful post-Katrina annals and could severely test efforts to mend the police department's frayed relationship with the public.

One officer is accused of fatally shooting a mentally disabled man in the back before a sergeant stomped on him. Prosecutors say the same sergeant, armed with an assault rifle, fired on wounded and unarmed people lying on the ground. All are accused of participating in a cover-up that allegedly included a plot to plant a gun, fabricate witnesses and falsify reports.

"It's going to be a painful process for this whole community to see the depths to which the police department had fallen to," said Rafael Goyeneche, head of an independent police watchdog group in New Orleans. "But I also think it's absolutely necessary to bring officers who betrayed the public trust to justice."

The group was dubbed the Danziger Seven after they were charged in state court with murder or attempted murder in December 2006, but a judge threw out all the charges in August 2008. Federal authorities then began their own investigation a month later, which led to charges against the Danziger Seven and four others.

The Danziger Bridge shootings broke out the morning of Sept. 4, 2005, less than a week after flooding from broken levees plunged New Orleans into chaos. After hearing a radio call that other officers were taking fire, a group of officers working from a makeshift station piled into a rental truck and drove to the bridge, which connects two neighborhoods hit hardest by flooding.

Prosecutors' account of what happened next is outlined in court filings that accompanied guilty pleas last year by five former officers, including Danziger Seven members Michael Hunter, Robert Barrios and Ignatius Hills. All five admitted participating in the cover-up.

Hunter, who drove the rental truck, says he fired warning shots when he saw a handful of people casually walking on the east side of the bridge. The people scattered and took cover behind a concrete barrier. As the truck stopped, an unidentified sergeant allegedly fired an assault rifle at a man who raised his head above the barrier but didn't appear to be armed.

Hunter says he exited the truck and saw the sergeant and at least one other officer firing at the barrier. They initially complied with his order to stop shooting, as he believed there was no threat. But the sergeant "suddenly leaned over the concrete barrier, held out his assault rifle, and, in a sweeping motion, fired repeatedly at the civilians lying wounded on the ground," according to an April 2010 court filing.

Police shot and killed 17-year-old James Brissette on the east side of the bridge. Hunter hitched a ride with a state trooper to the west side of the bridge, where they saw Lance Madison and his 40-year-old mentally disabled brother, Ronald, running away.

As the trooper's car stopped, an unnamed officer fired a shotgun at Ronald Madison's back. As Madison lay dying on the pavement, the sergeant repeatedly kicked and stomped on him "with as much force as he could muster," the court filing says. Prosecutors say neither brother was armed.

Yet Lance Madison was arrested on charges he tried to kill officers. He was jailed for three weeks but released without being indicted.

The officers have claimed they opened fire only after being shot at. They point to testimony less than a month after the shootings by Lance Madison, who said a group of teenagers fired at him and his brother before they encountered police.

Prosecutors, however, claim police immediately embarked on a brazen cover-up because they knew they had shot unarmed residents.

Jeffrey Lehrmann, a former detective who pleaded guilty to participating in a cover-up, says he helped craft and document false stories about the shootings, using Katrina's hardships as an excuse for gaps in the probe.

The remaining four Danziger Seven members — Sgts. Robert Gisevius and Kenneth Bowen, officer Anthony Villavaso and former officer Robert Faulcon — will be tried on charges related to the shootings.

Two other officers — retired Sgts. Arthur Kaufman and Gerard Dugue, who investigated the shootings — are charged with participating in a cover-up. Kaufman will be tried along with the four Danziger Seven members. Dugue will be tried separately.

Henry Dean, a New Orleans police commander and president of the local Fraternal Order of Police, said the rank-and-file's support for the accused officers hasn't waned since the day they were greeted with applause outside the jail.

"The way it's expressed has changed, that's all," Dean said.

But he conceded the Danziger case and several other Justice Department probes of alleged police corruption in New Orleans have eroded the public's trust.

"It has made their job a little more difficult," Dean said.

A judge has refused to move the trial despite defense claims that the officers can't get a fair trial in New Orleans because of widespread news media coverage of this and other cases, including last year's trial in the post-Katrina death of Henry Glover, 31. A jury convicted a former officer of manslaughter for shooting Glover and found another guilty of burning his body in a car.

The judge also has ruled out any general testimony about the chaos after the storm, when helicopters were plucking stranded residents from rooftops, looting was rampant and dead bodies littered the city. Many officers abandoned their posts. Those who stayed endured harsh conditions, with little sleep and few ways to communicate.

Andrea Celestine, a sister of Danziger shooting victim James Brissette, said months passed before her family could confirm he was dead. And they didn't know police were responsible until a New Orleans prosecutor approached them about a year after Katrina. She said her mother has waited to hold a funeral until the trial is done.

"It's just so senseless," she said. "It's almost like they were using them for target practice."