'No justice, no peace." From Oakland to New York, from Baltimore to Nashville, demonstrators shut down city centres across the United States in the largest civil rights protests for a generation.

But by Thursday, as a blanket of sleet covered the country and people drifted off to celebrate Thanksgiving with their relatives, the energy, if not the anger, had dissipated and justice remained as remote as ever.

Although they were responding to a Grand Jury's decision not to charge police officer Darren Wilson with any crime for shooting an unarmed teenager, the thousands of people who took to the streets were not marching for Michael Brown - or not only for him. In death, he represents every African-American life cut short by police, every "justifiable homicide" with no consequences for the killer.

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So in Ohio they marched for Tamir Rice, a 12-year-old boy with a toy gun who didn't raise his hands fast enough, and for John ­Crawford, who made the mistake of taking an air rifle off the shelves at Walmart and carrying it with him as he shopped. In California they marched for Alejandro Nieto, a security guard who was having dinner in the park when he was shot 14 times by officers who believed that he had aimed a taser at them.

In New York, they marched for Akai Gurley, a young father shot in the chest by a rookie patrolman as he climbed the stairs at the housing estate where he lived, and for Eric Garner, asphyxiated by police as they arrested him on suspicion of selling untaxed cigarettes.

Normally, these would be local tragedies, with few repercussions for anyone but the families and communities torn apart. But in the aftermath of Brown's death, activists are making the connections to produce a systematic record of unarmed black men killed by police: Derrien Hunt in Salt Lake City, Ezell Ford in Los Angeles, Joshua Paul in Carpentersville… All died this year. None was carrying a deadly weapon. And so far, no police officer has been held accountable for their deaths. There are far too many others to list here.

"No matter what the c­ircumstances are, they kill us intentionally and get away with it," said New York State Assemblyman Charles Barron. "Cops don't get indicted, and then after the indictment, if we're lucky to get that, they don't get convicted. The ­judicial system is fatally flawed."

The case of Garner is the next likely flashpoint. As in Ferguson, District Attorney Daniel Donovan has convened a Grand Jury, promising a "fair, thorough and responsible investigation". As in Ferguson, the chances of an indictment are slim.

Announcing the decision not to charge Wilson, St Louis County prosecutor Robert McCulloch cited contradictory eyewitness statements and drew heavily on the officer's own recollection of events. This will be harder in Garner's case, because the fatal encounter was filmed by a bystander.

In the video, Garner is exasperated but also polite. "Every time you see me you wanna harass me. I'm minding my business, officer," he says. "Please just leave me alone." One policeman, Daniel Pantaleo, wraps his arm around Garner's neck and several others wrestle him to the pavement. Garner tells them "I can't breathe" - 11 times in all.

Garner was a big man, and obese. He suffered from diabetes and severe asthma. The medical ­examiner's report determined that while these conditions may have been contributing factors, what caused his death was compression of the neck and chest.

When the video surfaced, both New York Mayor Bill de Blasio and his Police Commissioner, William Bratton, described Pantaleo's grip as a "chokehold" - a procedure that the New York Police Department banned in 1993.

Patrick Lynch, president of the Patrolmen's Benevolent As­sociation, said Pantaleo used an approved restraint technique and called Bratton's decision to temporarily strip the officer of his badge and gun "a completely unwarranted, knee-jerk reaction for political reasons".

In 2010, the most recent year for which records are available, federal grand juries issued an indictment in 161,989 of 162,000 criminal cases. But Staten Island, where Garner lived and died, is home to a greater concentration of police officers and their families than any other borough in New York, and District Attorney Donovan is dependent on their goodwill.

Unless he recommends charges, Pantaleo is likely to walk free.

There is a precedent. In 1994, Ernest Sayon died after a drug raid on Staten Island. The c­oroner ruled his death a homicide by as­phyxiation, but police said he hit his head on a cobbled street, and after seven months of considering the evidence, a grand jury decided no charges were warranted.

In a chokehold case in the Bronx in the same year, Officer Francis Livoti was cleared by a grand jury of culpability in the death of Anthony Baez, only to be charged with civil rights violations, convicted, and sentenced to seven years in prison.

This is now the only way that Wilson can be held to account for Brown's death, but in order to make the charge stick, federal ­prosecutors would have to prove that he intended to deprive Brown of his civil rights, based on his race - a hard standard to meet.

According to the FBI, there were 461 "justifiable homicides" in 2013, but this figure is known to be a serious undercount because many states, cities and counties fail to report their data. By collating local news reports, the website Killed By Police provides something closer to the true figure: 950 so far this year and 1709 since May 2013.

Most were justifiable. As Lynch pointed out, being a policeman is "a difficult and complex job" in a country awash with guns, and benefit of the doubt "has long been part of the social contract that allows police officers to face the risks".

But the recent spate of shootings shows the balance has tipped. In all but the most glaring, un­deniable instances of misconduct, police have complete impunity.

From top to bottom, the law provides protections for officers who kill. In June, the Supreme Court ruled policemen did not use "excessive force" when they fired 15 shots into a car they had been pursuing, killing the driver and a passenger.

Missouri law states that as long as an officer "reasonably believes" that a person has ­committed or intends to commit a felony, he may shoot to kill if it is "immediately necessary to effect the arrest".

Of the 14 police shootings in St Louis County since 2004, 10 were ruled justified by an ­internal investigation, four went to a Grand Jury and no charges were pressed.

St Louis City police killed 39 people from 2003 to 2012. Only one officer was indicted - and acquitted.

In appealing for calm after the verdict was announced in Ferguson, President Barack Obama conceded police sometimes unfairly singled out African-Americans - "communities of colour aren't just making these problems up" - but denied that this amounts to structural racism.

Does the system treat blacks and whites differently?

"I don't think that's true for the majority of communities or the vast majority of law enforcement officials," he said.

The data suggest otherwise. One in three black men in the United States will go to prison during their lifetimes.

A ProPublica investigation found that from 2010-12, African-American teenagers were 21 times as likely as their white peers to be killed by police.

This is a slightly misleading statistic, in that it is based on the flawed FBI data, and does not account for the fact that black teens also commit many more crimes, but at the least, it indicates a deeply troubling racial disparity.

As Ferguson burned on Monday night, one of the most memorable images was a squad of riot police, equipped with the latest military hardware, massing under the Christmas decorations of the city's main drag - Seasons Greetings spelled out in red tinsel and fairy lights. Almost all the ­officers were white.

Police in Ferguson arrest the city's black residents at a rate nearly three times higher than non-blacks, but the department is hardly an outlier.

A USA Today analysis showed more than 1500 police forces arrest African-Americans at a rate even more skewed.

At least 70 police ­departments are 10 times as likely to arrest blacks as they are to arrest people of other races.

No wonder there is a "deep and festering lack of confidence in the fairness of the justice and law enforcement systems," as the United Nations High Commissioner for Human Rights put it. Zeid Ra'ad Al Hussein said he was "deeply concerned at the disproportionate number of young African-Americans who die in encounters with police officers".

It has been a week to read James Baldwin, the great African-American novelist and social critic who once observed that "to be a Negro in this country and to be relatively conscious is to be in a rage almost all the time".

This was in 1961, before many of the civil rights movement's most significant gains, but the tumult in Ferguson - the justifiable anger, to borrow some terminology - was a reminder that his words are as relevant as ever. "The law is meant to be my ­servant and not my master," he wrote, "still less my torturer and my murderer."

As a teenager, Obama studied Baldwin. As a community organiser, he was outspoken about the impact of racial bias in Chicago. But as president he often seems constrained, too aware of the cost in white votes of speaking his mind. No doubt he has seen the polls that show how sharply divided responses to Brown's death are.

In a HuffPost/YouGov survey, 64% of black Americans blamed Wilson, compared with just 22% of whites, who were more than seven times as likely as blacks to say that the shooting was justified.

"Who cares whether they call him a racist? We are dying," said Barron. "It may cost him white votes but it's costing us black lives. Which is more important?"

Last Thursday, four days before the Grand Jury cleared Wilson, Akai Gurley was walking up a dark ­stairway with his girlfriend at the Louis Pink houses, a notoriously rough council estate in East New York.

Two young policemen were coming the other way, on a "vertical patrol" of the building.

For some reason, Officer Peter Liang fired a single shot, hitting Gurley in the chest, mortally wounding him.

The cops retreated, back up to the eighth floor, and Gurley staggered down to the fifth floor, where he collapsed.

The next day, NYPD Commissioner Bratton described the incident as an "accidental discharge" and promised a full investigation.

On the landing where the young man fell, above the prayer candles and messages of condolences, ­somebody had sellotaped their own verdict: "We are all Akai Gurley. This whole damn system is guilty!"