Some time before midnight on Tuesday, a peaceful but tense crowd protested before a line of police and National Guard in front of the Ferguson police station.
It was cold, just on freezing, and the two parties had been facing off since sunset. While most in the crowd were calling for peace, some wanted confrontation, and they were getting bored.
Overhead a police chopper described lazy circles in the sky and it soon became clear its spotlight was fixed on a nearby location.
The result was predictable but grimly fascinating to watch nevertheless.
A few young men broke away and headed off to find the light. Others followed in twos and threes and then, as though drawn by surface tension, the crowd moved, its front ranks breaking from march to canter to run as they turned a corner. It was like a drop of water gathering bulk and pace as it found its way down a windowpane.
In front of the Ferguson City Hall the frontrunners joined a smaller group that had set upon a police car. They shattered its windows with thudding kicks and stones torn from the border of a garden bed. They lifted it on to its side and stepped back before it fell with a sprinkling thud on to its wheels again.
After long seconds police in squad cars and National Guard in armoured personnel carriers arrived and formed ranks marching forward, some spraying mace at those too slow to flee.
The town hall, with its Christmas dioramas silhouetted behind floor-to-ceiling windows, was saved.
This week you could rack a moment like that up as a success for police in Ferguson, but you don't have to look hard for the metaphor.
The violence followed the police spotlight.
Rallying point
It wasn't meant to be this way. There had been hope that the United States' election of a black president signalled the beginning of the end of the racial division that has tormented the nation since its creation.
Instead, the president's race became a rallying point for the most extreme of his opponents, who appeared to believe it rendered him ineligible for office.
For years Barack Obama has ignored the race baiting of elements of the far right, in public referring to it only in jest.
"Let's face it, Fox, you will miss me when I'm gone," he said at the last White House Correspondents' Association dinner. "It will be harder to convince the American people that Hillary was born in Kenya."
Laughable as they are, the birth conspiracies and the racism they reflect have cast a shadow over Obama's presidency.
Soon after coming into office he was to realise that far from helping the US overcome racial tension, his presence had the capacity to inflame it.
This became clear to the world after the killing of Trayvon Martin, an unarmed African American boy who was shot dead near his father's home by neighbourhood watch volunteer George Zimmerman.
Martin's killing by Zimmerman provoked nationwide protest among African Americans, not so much for the shooting but for the fact police did not even charge Zimmerman with a crime for six weeks, presuming that under Florida's "shoot first" self-defence laws he had committed no crime. In the end Zimmerman was charged and found not guilty, a result that prompted outrage and protest, though not riots.
When the President eventually discussed the case, he observed: "I can only imagine what these parents are going through, and when I think about this boy I think about my own kids, and I think every parent in America should be able to understand why it is absolutely imperative that we investigate every aspect of this and that everybody pulls together, federal, state and local, to figure out how this tragedy happened."
And he added: "You know, if I had a son, he'd look like Trayvon."
The observation infuriated many conservative Americans. In a comment typical of the tone Newt Gingrich, then a presidential candidate, thundered, "Is the President suggesting that if it had been a white who had been shot, that would be okay because it wouldn't look like him?"
Obama must have already known that his expression of empathy for the parents of a dead black child would provoke anger in some.
In the first year of his presidency race had exploded as an issue for the White House in the most unlikely of ways.
The famed African American Harvard professor Henry Louis Gates jnr had just arrived home and found his front door jammed when a local police sergeant, James Crowley, came across him. Rather than helping him open the door, Crowley suspected Gates of being a burglar and arrested him.
In the ensuing controversy Obama remarked that the arrest was "stupid". The comment became the first serious blow to his presidency. The outrage that Obama might side with an African American arrested by a white cop was so prolonged and intense that the White House finally tried to end it with a so-called "beer summit" - an excruciatingly awkward meeting between Obama, the cop and the professor at the White House over a beer.
"My hope is that as a consequence of this event this ends up being what's called a 'teachable moment', where all of us, instead of pumping up the volume, spend a little more time listening to each other and try to focus on how we can generally improve relations between police officers and minority communities, and that instead of flinging accusations we can all be a little more reflective in terms of what we can do to contribute to more unity," Obama said.
It was a teachable moment too, though perhaps not in the way the president had hoped. Obama learnt to discuss race very rarely and very delicately – he barely touched on it again until Martin was shot dead. African Americans learnt that just because there was a black man living in the White House they should not expect rapid change.
Asked about Obama during riots in Ferguson in August, one young man on the street told Fairfax Media: "'I ain't got no thoughts on him. Where he at? Where he at?
"Get him the f**k out of here. I still ain't got insurance. F**k that nigger."
Racial divide
The racial divide in the US is perhaps most easily quantifiable in the criminal justice system.
African Americans are incarcerated at six times the rate of whites and make up 1 million of the US's 2.3 million incarcerated. Obviously the factors that can lead a person into prison are myriad, but one thing is clear - blacks are far more likely than other citizens to come into contact with police.
Over the past decade New York police pursued a strategy of "stop and frisk" to crack down on crime. The policy has been discredited and is winding down rapidly. At its height though the NYPD stopped and searched 500,000 people on the street without cause each year. About 12 per cent of them were white.
Many police forces around the country adopted similar tactics, though not always as systematically.
The impact of the policy on crime is contested, though crime rates across the country have been falling steadily since 1990.
What is clear though is that the constant searches have intensified the fear and mistrust many African Americans, particularly young black men, have for authorities.
In this toxic and hostile environment the explosion of violence after the unarmed teen Michael Brown was shot dead by a white police officer in Ferguson, and again after it was decided the officer would not face charges, is not surprising.
In Ferguson on Wednesday morning Tiffany and Ronald Singleton were standing in the snow across the road from a beauty supply shop that had been burnt to the ground in riots two nights before.
Police watched from the corner as the couple described what a typical stop is like.
"As soon as they get out of their cop cars they are reaching for their handcuffs and they cuff you while they question you and they don't read you your rights," Tiffany Singleton, 41, said. "They let you stand there, they call back to the police station and then they might let you go, depending on if you have a warrant or not, depending on if someone at the station wants you."
Ronald, 34, estimated he was stopped twice a month and he smiled and shook his head in wonder when a reporter told him he couldn't remember ever being stopped by a police officer as an adult.
Like many in Ferguson, Ronald does not believe Wilson had any cause to stop Brown the day the officer shot him, though evidence shows he recognised him as fitting the description of a young man who minutes earlier had stolen cigarillos from a liquor store.
And the couple believed Brown's reaction to the stop – apparently one of aggression – was the right one.
Asked what the correct response to an officer in Ferguson was, Tiffany explained: "[You say] 'f**k you' and keep walking."
Roland said: "What Mike did, he did the right motherf**king thing, cos I would have done the same motherf**king thing my damn self. Me being a black American, that's the right thing."
During the days of protest and violence after Brown was shot, and again after Monday's grand jury decision, many observers tried to distinguish between "the real" protesters, who according to this line of reasoning were local and non-violent, and "the trouble-makers", who had come to town to incite violence for the atavistic joy of it.
That distinction was not made so commonly on the streets.
On the fringe of a rally on Tuesday night Darnell Singleton, a documentary maker who lives in Ferguson and has been protesting and filming since the shooting, explained in front of the police station that everyone in the chanting crowd before us was angry, just that some were more mature than others.
"When you twist the pitch fork in their heart, some of these young men are going to lash out," he said.
Others said the violence was spurred as much by hopelessness as anger.
"It's one thing if he [officer Wilson] went to trial and they said he was innocent, but saying you don't even have to have a trial for shooting a black man, that's another thing," student Jashyra Robinson, 22, said. "That's what hurts me the most."
The day after the riots and fires in Ferguson the protests spread across the nation. This was no accident. Ever since Brown was shot dozens of protest groups have been gathering and organising under various umbrella groups. Many organisers do not see the movement as simply a reaction to the shooting, but as the next chapter of the ongoing civil rights movement.
Their slogans and evolving tactics reflect that. The crowds still chant "Hands up, don't shoot", but as they block the roads in Ferguson they are as likely to be yelling at police, "Who shuts shit down? We shut shit down". Across the country protesters have begun blocking roads as an act of civil disobedience.
Some see hope in the idea of a new generation taking up the civil rights movement, but that optimism is limited.
Professor Cornel West, a leading African American activist and trenchant critic of Obama, was asked his view by CNN this week.
"Ferguson signifies the end of the age of Obama," he replied. "It's a very sad end. We began with tremendous hope and we end with great despair."
