Case is one of many dealing with alleged police corruption and brutality amid the law and order breakdown after Katrina

There's not much mystery about how Henry Glover ended up a charred corpse in a burned-out car in the heart of New Orleans. One police officer has admitted to shooting the young black man. Another has confessed to throwing flares into the car where Glover lay covered in blood on the back seat. He then put a couple of shots through the window as the vehicle was consumed by fire. The officer has since called that "a very bad decision".

Glover's body was not recovered for weeks and proved so difficult to identify that it was nine months before his family could bury him. But it has taken five years to bring anyone to trial, and only then after the federal authorities waded in with accusations of an institutional cover up that continues to this day.

Glover died during the chaotic days after Hurricane Katrina breached the city's levees, flooding New Orleans and unleashing a wave of looting and violence. Five policemen are on trial over his death, but also in the dock are the city's police department and local judicial system as a jury is asked to consider whether the devastation wrought by the hurricane in 2005 also blew away the rule of law.

One police officer, David Warren, is accused of shooting Glover without legal cause. Greg McRae is charged over the burning of the car and the beating of men who tried to help the victim. A third policemen is also accused of the beatings, while two others face accusations of falsifying evidence to cover up the crimes.

"They believed that, after the storm, no one was watching," Tracey Knight, a prosecution lawyer, told the court. "They were convinced that no one cared about Henry Glover and how he died."

The accused are among 20 New Orleans police officers charged in recent months over killings, assaults and the fabrication of evidence during Katrina. They are being prosecuted by the federal government under civil rights legislation after local authorities proved unable or unwilling to act.

Among them are six officers who face trial after the police opened fire on local people as they crossed a bridge trying to flee the floodwaters. Two were killed and four others wounded.

Federal prosecutors and civil rights lawyers say that Katrina laid bare a culture of corruption, racist violence and a code of silence in the New Orleans police department (NOPD). They describe a force in chaos: while some officers were dedicated to saving lives, others armed themselves with their own automatic weapons and behaved like vigilantes; senior officers spread false assertions that martial law was declared and encouraged the shooting of looters.

At least 10 people died at the hands of the police. Some civil rights lawyers suspect the real figure is much higher. All the victims were African Americans.

The defendants claim that those were exceptional times in which officers feared for their lives and were under orders to bring an end to the anarchy that consumed the city.

Warren was assigned to guard a shopping centre from looters with Linda Howard, a fellow officer who told the court that Warren had armed himself with his personal semi-automatic rifle.

"I asked him what did he want that for? He said: 'For protection,'" said Howard. "At one point Warren said: 'Do you know we're under martial law?' I said: 'I don't know anything about martial law, but I do know that the laws you had before the storm are the same ones you have to follow now.'"

When Glover arrived at the shopping centre with another man in a four-wheel drive and the pair looked as if they were about to load looted goods into the vehicle, Warren shouted at them.

"It was a loud command telling them to get away," said Howard. "They were startled. They ran away … toward the street. I could see Warren levelling his weapon and a shot rang out. And the gentleman ran and collapsed in the street. I asked him: 'What did you do that for? He said: 'I didn't hit him'. I said: 'Yes you did'."

Warren says that he felt threatened because Glover was storming at him with something in his hand that could have been a weapon. But Howard said the victim was heading in the other direction and that she didn't reach for her weapon "because I didn't feel threatened". A photograph displayed in court shows Glover with a bullet hole in the middle of his back.

Another officer testified that in the aftermath of the hurricane Warren told him that looters "were all animals and they deserved to be shot".

Some officers say that their superiors, including Warren Riley, the second in command of the force, had told them to "take back the city and shoot looters". Ray Nagin, then mayor of New Orleans, spoke of martial law even though there was no legal mechanism to declare it.

As Glover lay bleeding in the street, he was picked up by three men, including his brother, and driven off to obtain help. They stopped at a local school occupied by a police special operations unit. Prosecutors say that the men were handcuffed and beaten by McRae and another police officer.

William Tanner, the car's driver, testified that he was hit with a rifle butt and subjected to racial abuse by one of the accused police officers. Then McRae climbed into the car, drove it to the other side of a nearby levee and set it on fire with Glover inside. A fellow officer told the court that McRae was laughing as he ran away from the burning body.

Glover's charred corpse remained in the burned out car on the levee for several weeks. Two hurricane recovery workers filmed the vehicle and captured footage of Glover's skull with two small holes in it. By the time the car was recovered, the skull was gone.

The prosecution contends that McRae burned the body to cover up the shooting and that superior officers then colluded to cover up both crimes.

Howard told the court that in the immediate aftermath of the hurricane there was only a cursory investigation of the shooting and that she felt intimidated not to implicate a fellow officer. "After the shooting it was very upsetting to me because of the way it was handled. I didn't know who to trust, who I could believe, who to talk to," she said.

The trial heard from other police witnesses how their superiors did not investigate the shooting, telling officers that "police need to stick together".

Mary Howell, a respected civil rights lawyer who has challenged the actions of the New Orleans police department for more than three decades, said that the local authorities have for years been reluctant to prosecute police officers for murder and other crimes.

"Part of this is the political difficulty in getting a state district attorney, who is an elected official, to prosecute police officers when they rely upon the police department to make their cases in state court and, historically in New Orleans, the state officials have always been not just hesitant or reluctant – they have actually refused to prosecute criminally in these cases," she said.

But Peter Scharf, a renowned New Orleans criminologist and author of The Badge and the Bullet: Police Use of Deadly Force, is dismissive of the contention that officers felt they were unaccountable because of endemic corruption in the police. He says that the circumstances in which they found themselves were almost unprecedented in modern America: there was a total collapse in the leadership of the police force while officers were confronting anarchy and devastation on the streets.

"These officers are not angels: they're flawed, they're rough, they're crude. I totally believe all that. But there was a horrible failure of multiple layers of leadership, an implosion of responsibilities at all levels. It's not to defend these actions; it's to put them into context. If you criminalise individual behaviour for what is essentially a system breakdown, there's a problem with that," he said.

"Is this a political trial or a criminal trial? Are they trying to make a point about race relations? Are they trying to create a social objective – clean up the NOPD – through a legal process? That's my suspicion. Political trials are often bad justice."