A demonstrator walks through smoke launched by police after a skirmish in Ferguson, Missouri.

Ferguson, Missouri - Vandals attacked stores in Ferguson early on Saturday, hours after police said the unarmed black teenager shot dead by a white officer in an incident that unleashed days of rioting was a robbery suspect.

The allegation reignited anger in the town, a St. Louis suburb in the state of Missouri that has endured on-and-off rioting since 18-year-old Michael Brown was killed on August 9.

Police released surveillance footage showing a tall, muscular black man - in a T-shirt, khaki shorts and sandals, the same outfit Brown was wearing - grabbing a convenience store clerk by the shirt and shoving him. Bown allegedly stole a $49 box of cigars.

Following a peaceful demonstration that ended around midnight Friday (0500 GMT), groups of rioters struck several stores, including a cell phone store and a meat market, the St Louis Post-Dispatch and other local media reported.

Police in some areas fired tear gas and smoke bombs, but mostly stayed at a distance in armoured vehicles and riot gear, according to news reports.

In several instances, locals rushed to the stores being raided and convinced the looters to stop stealing and leave, then stayed to prevent the thieves from returning.

“If you're getting conflicting reports, it's because there's chaos here. It's dead in some areas, crazy in others.#Ferguson,” wrote BuzzFeed reporter Joel Anderson on Twitter.

A barrier of locals stood outside the store that Brown allegedly stole from and stopped looters from breaking in, CNN reported.

The owners of one looted store, angry that police did not intervene, showed up with handguns and rifles, various news outlets reported.

The link between Brown and the “strong-arm” theft of a box of Swisher Sweet cigars, about 20 minutes prior to the Saturday shooting, appears in a police report summarising the content of a surveillance video.

“The video reveals Brown enter (sic) the store” with his a friend and engaging in “an apparent struggle confrontation” with a store clerk.

“It is worth mentioning that this incident is related to another incident (in which) Brown was fatally wounded involving an officer of this department,” the report added.

Through their lawyers, Brown's family said they were “beyond outraged” at what they called a “devious” attempt to smear the character of their son, who had no criminal record and was about to start vocational college.

“There is nothing based on the facts that have been placed before us that can justify the execution-style murder of their child by this police officer as he held his hands up, which is the universal sign of surrender,” the lawyers added.

Ferguson police chief Thomas Jackson identified the officer who shot Brown as Darren Wilson, 28, a white, four-year veteran of the force with no record of ill-discipline.

“Initial contact between the officer and Mr Brown was not related to the robbery,” Jackson said later.

Wilson - in a patrol car - stopped Brown “because he was walking down the street, stopping traffic. That was it,” Jackson said.

Wilson's home in a mostly white town some 18 miles from Ferguson has been under police protection, but neighbors told the Washington Post that the officer got “spooked and took off pretty quickly before the name was announced.”

Jackson said he released the incident report and video because he had received “too many requests” from news media under freedom-of-information laws.

Local residents however suspected an attempt by Ferguson police to rewrite the narrative just as St Louis County police and the FBI conduct parallel investigations.

“I think they're covering up a lot of things,” said one woman, interviewed on CNN, who did not want to give her name. “They're covering up for this officer... Why wasn't this said in the beginning?”

In the past week, protests escalated into confrontations with county police who donned military-style combat uniforms, armed themselves with assault rifles, tear gas and rubber bullets, and deployed armoured vehicles.

Missouri Governor Jay Nixon ordered state troopers to take over from the distrusted local police on Thursday, which briefly helped calm the situation.

The new operation is headed by Captain Ron Johnson of the Missouri State Highway Patrol, an African-American officer who became an instant hero for meeting protesters in person even shaking hands and hugging some of them.

FBI agents, working with attorneys from the Justice Department's Civil Rights Division and US Attorney's Office, meanwhile interviewed witnesses on the scene at the time of the shooting, officials said.

In the coming days, FBI agents will “be canvassing the neighborhood where the shooting took place to identify any individuals who may have information related to the shooting,” a Justice Department statement said.

Separately, protesters sprayed graffiti and broke windows as they marched late Friday in heavily black Oakland, California, against the abuses in Ferguson. Riot police came out in force, according to news reports, but were restrained in their response and there were only minor clashes. - Sapa-AFP