Michael Brown, the unarmed teenager killed by a police officer in the Missouri city of Ferguson, was shot multiple times and finally felled by a mortal wound to the head, according to a preliminary autopsy and an account of the shooting provided by the officer, Darren Wilson.



The disclosures came on a night marred by shootings and clashes between protesters and police, the worst in eight days of turmoil, which terrified residents and left Ferguson resembling a war zone.



A violent altercation between protesters at around 9pm, which left a woman with a gunshot wound, triggered a swift response from police who had been preparing to enforce a curfew at midnight.

Officers fired multiple rounds of tear-gas and swept into the centre of Ferguson, prompting chaotic scenes as protesters and onlookers tried to flee. There were no immediate details about casualties.

Facebook Twitter Pinterest A woman has her face doused with milk after suffering the effects of tear gas used by police in Ferguson on Sunday night. Photograph: Joshua Lott/Getty Images

Sunday’s revelation of an autopsy report of the 9 August killing, which has polarised opinion across the US, threatened to inflame tensions further. Brown, 18, was shot at least six times, including twice in the head, according to a preliminary private autopsy performed on behalf of his family on Sunday, the New York Times reported.



One of the bullets entered the top of the skull, suggesting his head was bent forward when it struck and caused a fatal injury, according to Michael Baden, a former chief medical examiner for the City of New York. He flew to Missouri at the family’s request to conduct the autopsy, which follows an earlier examination carried out for St Louis County, which is investigating the killing.



Tear gas and smoke fills the air as unrest continued in Ferguson, Missouri on Sunday night. Photograph: Joshua Lott/Getty Images

Baden said it was probably the last bullet to hit the teenager. Brown was also shot four times in the right arm. All bullets were fired into his front, the examiner concluded.



The absence of gunpowder on the body suggested the bullets were not fired from close range. That determination could change if there was gunshot residue on Brown’s clothing, to which Baden did not have access, he told the New York Times.



The autopsy’s revelaton that Brown was shot in the head mirrored Wilson’s account of the disputed incident, when he encountered Brown walking in the middle of a street in Ferguson with a friend, Dorian Johnson.

Facebook Twitter Pinterest A protester runs through a clowd of tear gas in Ferguson, Missouri. Photograph: Scott Olson/Getty Images

Wilson has not spoken publicly but a friend of the family, who declined to be named, told the Guardian that the officer admits he shot Brown in the head. However, his version of events contradicts aspects of the accounts given by some other eyewitnesses, including Dorian Johnson.

There appears to be little dispute that an altercation took place when Wilson encountered Brown and Johnson, shortly after a robbery at a convenience store. Brown then made off, but quickly turned back.

In Wilson’s version, Brown was moving towards the officer in a threatening manner when he was shot. The autopsy concludes that all the shots were fired from the front.

Wilson’s account is that Brown continued to move towards him even after the first shots were fired, and did not stop until suffering a mortal wound to the head. “He just kept coming,” the friend said, characterising Wilson’s account.

The Department of Justice, which is leading a civil-rights investigation into the killing, on Sunday took the unusual step of ordering a federal medical examiner to conduct a third autopsy on Brown’s body. A spokesman for Eric Holder, the attorney general, cited the “extraordinary circumstances” of the case for the decision.

Both sides in what is becoming an increasingly incendiary and politicised story are likely to offer different interpretations: that Wilson fired in self-defence; or that six bullets showed excessive force.



Friends of Wilson and his girlfriend, Barbara Spradling, also a Ferguson police officer, have expressed concern about the racial and institutional politics involved, worrying that the charged environment may unduly influence the case.



In addition to concerns for their safety, friends of Spradling and Wilson believe his reputation has been unfairly tarnished by a rush to judgment from the media and some members of the public.



One friend of Spradling believes the legitimacy of any evidence supporting Wilson’s version of events will be questioned by protesters.



Sunday night’s mayhem further poisoned the toxic relationship between police and Ferguson residents. It also raise urgent questions about Governor Jay Nixon’s decision on Saturday to declare a state of emergency and impose a midnight-to-5am curfew.



A coalition of civil rights groups condemned the move. The American Civil Liberties Union, the National Association for the Advancement of Colored People, the Legal Defense and Education Fund and the Lawyers’ Committee for Civil Rights Under Law said the order violated the constitutional right to free assembly.



The order fell short of legal requirements to define the area affected by the curfew, the groups said. “People have a right to know when and where their conduct is lawful under all circumstances, but especially when the government is restricting activities that are protected by the first amendment,” their statement read. “Restricting this most fundamental of all American values is not a solution to the problems in Ferguson.”



In St Louis, a crowd of about 150 people gathered in support of Wilson. Some wielded placards with messages defending the 28-year-old officer and his family, during the early-evening demonstration.



“He was doing his job,” said Kaycee Reinisch, 57, of Lincoln County, Missouri. “And now because of public uproar in Ferguson, he is being victimised. He is being victimised by the whole city, the state and the federal government.” Reinisch said she had relations in law enforcement who would be “frightened to do their jobs” if Wilson were punished for the incident.



Earlier on Sunday Brown’s parents held a memorial service for their son at the Greater Grace Church. The veteran civil rights leader Al Sharpton told the packed congregation that the response to the death was a crucial test for US policing. “This is the defining moment in this country. All over the world, the debate is how the rights of people are dealt with by the state,” he said.