Mobile footage of events leading up to the incident
A former police officer in California has been charged with the murder of an unarmed black man at a railway station.
Johannes Mehserle, a transport officer at the time, is accused of shooting Oscar Grant, 22, in the back as he lay face down on a train platform.
Mr Grant was among several people taken off a San Francisco to Oakland train when police intervened to stop a fight.
The 1 January shooting, filmed on mobile phones, has provoked frequent and at times violent protests.
"At this point, what I feel the evidence indicates is an unlawful killing done by an intentional act and from the evidence we have there is nothing that would mitigate that to something lower than a murder," Alameda County District Attorney Tom Orloff said.
Johannes Mehserle was arrested in the neighbouring state of Nevada
It is rare for a murder charge to be brought against a police officer for an incident that happens while he or she is on duty, correspondents say.
Mr Mehserle's lawyer, Christopher Miller, said he was confident his client would be cleared, as "all the circumstances of that chaotic night become clear".
Video recorded by passengers on their mobile phones appear to show Mr Grant sitting calmly on the platform at Fruitvale station in Oakland after he and several others were pulled off a train by police.
He is then forced to lie face down, there is a struggle, Mr Mehserle draws his weapon and shoots Mr Grant once in the back.
Video of the shooting has circulated widely on the internet, increasing tensions between police officers and many African-American residents.
Oscar Grant's family have called for calm
Protesters have taken regularly to the streets. One demonstration last week turned violent, resulting in more than 100 arrests and damage to some 300 properties.
Mr Mehserle, who resigned a week after the shooting, worked for the Bay Area Rapid Transit (Bart) force.
He was arrested on Tuesday in the neighbouring state of Nevada, where he had gone after receiving death threats, his lawyer said.
On Wednesday, some 50 people were briefly moved out of the area after Mr Mehserle's parents found two suspicious packages in front of their house, local police said.
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