In a long and at times defensive statement, St Louis Prosecuting Attorney Robert McCulloch said the grand jury had not found probable cause to charge Ferguson police officer Darren Wilson for shooting Michael Brown dead after a confrontation in August.

He said despite early reports that eyewitnesses had reported seeing Mr Wilson shoot Brown dead after he raised his hand in surrender, physical evidence supported the police officer's claim that Brown had charged towards him before he was fatally shot.

Brown and his friend were stopped after Mr Wilson recognised them as fitting the description of two young men who had stolen cigarillos from a local convenience store.

The grand jury heard evidence that when stopped, Brown leant through the window of the car. During the confrontation two shots were fired. According to the evidence Mr Brown then ran from the car before turning and, according to one witness, "charge" back at Mr Wilson.

Mr McCulloch said the investigation had been complicated by the 24-hour news cycle and social media.

Mr Brown's death prompted protests almost immediately, not just for the shooting in a neighbourhood where the overwhelmingly white police force has a tense relationship with the majority black community, but for the reaction of the police afterwards.

Brown's body was left lying in the middle of the street for four hours while an increasingly angry crowd gathered.

That night protests spread, with some instances of violence and looting, prompting police to respond in force with the use of military equipment as well as riot gear. The unrest and provocative police response led the Missouri governor Jay Nixon to remove control of the scene from local police and turn it over to State Highway Patrol.

While the violence ended the street protests have remained in place for over 100 days. Tension has slowly increased as a grand jury has considered whether to charge Mr Wilson with a crime.

Police reinforcements have been prepared with special training and equipment including helmets, shield, batons, rubber bullets, pepper spray and smoke canisters.

Many of the protest groups have prepared too, training their members in civil disobedience and first aid. Organisers, loosely arranged into affiliated groups have outlined rules of engagement with police and "safe spaces" have been prepared for protesters to escape the cold or tear gas.

One of them, the Don't Shoot Coalition, consists of about 50 different groups. It has called on protesters to remain peaceful. The groups see the action in Ferguson as not only a response to Brown's killing, but to what they see as a culture of police violence against African Americans across the country.

Some see the protests in Ferguson as far more significant than a reaction to a single incident. On NBC's Meet the Press, guest Gwen Ifill of PBS called the unrest and violence the beginning of a "new civil-rights movement".

"There's a new civil-rights movement which has sprung up," she said. "These young people in the streets, these young people who created a social-media movement around Michael Brown, they're not saying pass a law, they're saying enforce the current ones."

In downtown Ferguson, a township on the outskirts businesses of St Louis, have closed and boarded up their windows while one of the area's school districts has shut down and local gun shops have reported a surge in gun sales from locals wanting to protect their homes.

Rather than charging Mr Wilson as he might have, Mr McCulloch chose to turn the decision over to a grand jury. Mr McCulloch's involvement in the case has been controversial, with over 70,000 people signing a petition demanding that he remove himself from the case because of his close family ties to the police and what some say is a long history of siding with the police against citizens. Despite rumours that Mr McCulloch would recuse himself or be replaced by Governor Nixon, the prosecutor has stayed on the case, though he has delegated the presentation of evidence to two senior attorneys in his office.

Some of the protesters were angered that Mr McCulloch did not recommend a specific charge against Mr Wilson, which is regarded by many as unusual. Without a charging recommendation, the grand jury can return an indictment on first- or second-degree murder, or either voluntary or involuntary manslaughter or no indictment at all.