NEW ORLEANS, Louisiana — Five New Orleans police officers indiscriminately shot unarmed residents during the chaos unleashed by Hurricane Katrina and got colleagues to help cover up the crime, prosecutors said Monday.

"Shoot first, and ask questions later," federal prosecutor Bobbi Bernstein said during opening arguments of a high-profile trial of the officers.

"That's how this whole case got started."

Bernstein described a "seemingly endless barrage of gunshots" that left two people dead and four badly wounded and a wide-ranging conspiracy that lasted almost four years.

The deadly 2005 shooting on the Danziger Bridge came to epitomize the city's failure to protect its citizens and exposed deep-rooted corruption in the police department, which critics say remains unaddressed.

"I was a police officer for 23 years," said Anthony Radosti, the vice president of the Metropolitan Crime Commission, a group that has played an unofficial watchdog role.

"And I'm appalled. We cannot have that in a civilized society."

Fear soon followed the deadly floodwaters which swallowed 80 percent of New Orleans and left thousands stranded on their rooftops after Katrina smashed through the city's poorly maintained levees on August 29, 2005.

Reports of widespread looting and armed gangs roaming the city shifted the government's already botched response from humanitarian aid to a military operation.

In the following days, six people -- almost all of them African American -- were killed under suspicious circumstances in incidents involving police. Scores more were injured.

The Danziger Bridge case is the most notorious of at least nine incidents being investigated by federal agents.

Defense attorneys gave a full-throated defense of their clients, depicting them as hero cops.

"These five had one thing in common -- they stayed," declared Paul Fleming, a lawyer representing Robert Faulcon.

He called the officers "proactive," saying, "They go out and get things done. They go out and get the bad guys."

Frank DeSalvo, the attorney who represents Sergeant Kenneth Bowen and has defended many NOPD officer in the past, called the government's case a work of "fiction" and compared it to a John Grisham novel.

DeSalvo and Flemming said that many of the government's witnesses were liars, singling out Michael Hunter, one of the officers who is set to testify against his former colleagues, and Lance Madison, a 20-year FedEx employee with no criminal record who watched his brother die that day.

Bernstein said ample evidence would be provided in the testimony of those caught in the crossfire, video from a nearby television crew and statements of three officers who have already pleaded guilty,

She described the terror experienced by one family, the Bartholomews, cowering behind a barricade as they "continued to feel more bullets rip through their flesh."

Four of the officers facing trial -- Sergeants Robert Gisevius and Bowen and Officers Anthony Villavaso and Faulcon -- were charged in 2007, by then-district attorney Eddie Jordan.

A judge threw out the case, citing prosecutorial misconduct.

The fifth defendant, Sergeant Arthur Kaufman, was not involved in the shooting, but faces charges for participating in the cover-up.

Much of the public supported the officers when they were first charged in 2007 and a crowd of more than a hundred people -- mostly off-duty officers -- rallied in their support on the day they turned themselves in.

But with new revelations of the extent of the violence and cover-up, public perception has changed. Several dozen protestors against police violence rallied outside the courtroom Monday.

While the case brought in 2007 likely would have pitted the words of civilian witnesses against police, in this trial five officers have already pleaded guilty and agreed to testify for the prosecution, which changes the dynamic.

Among the revelations that have already come out in guilty pleas are stories of secret meetings, the invention of non-existent witnesses, and the planting of a gun at the crime scene.

"This trial will help resolve the effectiveness of federal intervention," said Ursula Price, director of the city agency that was established as a result of community pressure post-Katrina for oversight of the department.

"If these prosecutions have real consequences it could lead to real change. We are waiting with bated breath."