Authorities named Darren Wilson as the police officer who killed an unarmed black teenager in Ferguson, Missouri, last weekend, saying the officer had a good record and the incident came in the aftermath of a robbery in which the teen was a suspect.

Wilson, who shot and killed 18-year-old Michael Brown on Saturday afternoon outside an apartment complex, had served six years on the force and had a good record, Ferguson Police Chief Tom Jackson said at a news conference yesterday.

Jackson said there had been a report of a robbery of cigars in a convenience store in the area a few minutes before Wilson encountered Brown walking down the street near an apartment complex.

The robbery suspect had been described as a black male wearing a white T-shirt, according to police records Jackson released yesterday. The deadly interaction was swift: Jackson said Wilson encountered Brown at 12.01pm and had shot him by 12.04pm.

About two dozen residents gathered at the news briefing by Jackson, and some were outraged that police suggested Brown was a robbery suspect when he was killed.

I don’t believe what the officer did was called for. Even if there was a robbery, it was unnecessary force to shoot an unarmed black man

“I think it was the right thing to do releasing the officer’s name, but for them to say this was an armed robbery makes me think this is a cover-up,” said Ferguson resident Milton Jackson, 37.

“I don’t believe what the officer did was called for. Even if there was a robbery, it was unnecessary force to shoot an unarmed black man,” he said.

Arthur Austin, 39, another resident, said: “This is how the police operate here; they always defame the name of the victim. Michael Brown had never been in trouble so it doesn’t add up. The more I hear, the less I trust what the police are saying.”

Protesters have also expressed anger over the fact that Brown’s bloodied body lay in the middle of a narrow residential street for several hours on August 9 after he was shot. But Jackson said yesterday that several officers and an ambulance had responded quickly to the scene and “assessed” Brown. His body was not moved for hours because the scene was being investigated and recorded, authorities said.

Police had held back naming Wilson for nearly a week because of fears he could be harmed amid a volatile and sometimes-violent week of angry protests that have followed Brown’s death.

Nixon told ABC News yesterday that the officer, who was placed on administrative leave, would be protected against any possible retaliation.

“I think that will be a step on the road to healing here and justice,” Nixon told ABC News.

The move to identify the officer comes after the American Civil Liberties Union sued St Louis County and the county police on Thursday, seeking copies of initial police reports of the shooting.

Civil rights leaders from around the country, community activists and protesters also demanded that the officer be identified and be held accountable for the killing.

Thousands of protesters demanding justice for Brown’s killing have clashed with riot gear-clad local police since Saturday, though there was a marked shift to a calmer tone on Thursday after the governor put an African-American Missouri Highway Patrol captain in charge of security for the area.

Rather than confront protesters with riot gear, rubber bullets and tear gas, a small number of police mingled with the crowd on Thursday night, urging a healing to the racially charged situation.

The protests cast a spotlight on racial tensions in greater St Louis, where civil rights groups have complained in the past of racial profiling by police, of the arrests of a disproportionate number of blacks and of discriminatory police hiring practices. Just three of the town’s 53-strong police are black, while two-thirds of its population of 21,000 are black.

The police version of the shooting differs markedly from witness accounts. Police have said that Brown reached into the police car and struggled with the officer who shot and killed him. They said Wilson was injured during the incident and was treated in a hospital for swelling on the side of his face.

But some witnesses have said Brown was trying to get away from the officer, who had tried to grab him after telling him to move off the road on to a pavement.

Witnesses said Brown held up his hands in a sign of surrender but was shot several times.