Several of the officers then chased Ronald and Lance Madison, two brothers, to the other side of the bridge, where Mr. Faulcon shot Ronald, a 40-year-old mentally disabled man, in the back. Sergeant Bowen was convicted of stomping him on the back as he lay dying.

No guns were recovered at the scene, and witnesses — both officers and citizens — testified that the victims were unarmed.

The cover-up began immediately, prosecutors said, and the jury found all of the officers, as well as retired Sgt. Arthur Kaufman, guilty on charges of obstructing justice, fabricating witnesses, lying to federal investigators or planting a firearm at the scene to bolster a made-up story.

While the jury convicted on all counts, it stopped short of considering the killing of Mr. Madison to be murder in connection with a firearms charge. Such a finding would have affected the sentencing range, though four of the defendants are nevertheless faced with potential life sentences. Mr. Kaufman faces up to 120 years. Sentencing is set for Dec. 14.

On the insistence of Judge Kurt Englehardt, the courtroom was nearly silent as he read guilty pronouncement after guilty pronouncement.

Family members of the defendants sobbed quietly. Outside the courthouse, Bobbi Bernstein, a deputy chief of the Justice Department’s civil rights division and the hard-charging leader of the prosecution, was in tears as she hugged Lance Madison, who was arrested during the cover-up of the shooting that left his brother dead. “I am thankful to have some closure after six long years of struggling for justice,” Mr. Madison said quietly.

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The verdict was long in coming, and followed a problem-plagued attempt by the Orleans Parish district attorney to prosecute the officers for murder, an effort that ended in a judge dismissing all charges in 2008.

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The federal prosecution began shortly afterward, and the Police Department as a whole began coming under more scrutiny. At one point there were at least nine federal criminal investigations into the Police Department’s actions, some of which are continuing; four have already led to indictments and three, including the Danziger case, to convictions.

In May 2010, the Justice Department announced a federal civil investigation into the department, an inquiry that has produced a scathing report on its practices and will eventually lead to a consent decree, a legally mandated blueprint for reform.

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Around 60 witnesses were called over the course of the monthlong Danziger trial, including victims, one of whom was unable to raise her right hand to swear in because she lost it as a result of the shootings on the bridge, and several officers who had been involved in the shootings and the police investigation and later pleaded guilty.

The trial was not only about these five officers but also about what exactly happened in the weeks after the hurricane, a sort of judgment on the initial widely held belief that the authorities were trying to control elements of a citizenry run rampant.

In the years since, that narrative has been qualified. While some people did turn to crime and violence, it has become apparent that some of the bloodshed and chaos was brought about by members of the long-troubled Police Department.

In opening and closing arguments, prosecutors portrayed the Danziger victims as people merely trying to survive when they were descended on by the police. Instead of assessing the threat when they arrived on the scene, prosecutors said, these officers tried to send a harsh lesson to people they had wrongly suspected of firing at the police.

“They thought they could do what they wanted to do and there wouldn’t be any consequences,” said Theodore Carter, an assistant United States attorney, in his closing statement. “This led to their crime, it led to their brazenness. It never occurred to them they were shooting up two good families.”

While some of the defense lawyers argued that the citizens were in fact armed, or that other people in the vicinity were shooting at the victims, their main argument was that the officers’ actions must be judged in the context of those first horrible days after Hurricane Katrina, when New Orleans was a city on the verge of anarchy.

As in a similar trial of the police last year, defense lawyers said that the officers should be considered heroes for staying in the city when so many others left and that, given the air of imminent and omnipresent danger in those days, their instincts should not be criminalized.

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“He has to decide and act in a split second, a nanosecond, to make a life or death decision,” said Paul Fleming, who represented Mr. Faulcon. Given the circumstances, he said, “It is a decision that is reasonable, it is a decision that is justifiable and it is a decision that is not a crime.”

Jim Letten, the United States attorney for Louisiana’s Eastern District, said that was exactly wrong. It is in situations like the anarchy after Hurricane Katrina, he said, when it is most crucial that the police be depended upon to protect citizens.

“Who can we count on when our society is threatened?” he asked. “If we can’t depend on them, who can we depend on?”