A pedestrian passes a mural on Thursday of Oscar Grant in Oakland, Calif., shortly before a jury delivered an involuntary manslaughter verdict in Johannes Mehserle's trial. (Noah Berger/Associated Press)

A former transit officer was convicted of involuntary manslaughter Thursday in the shooting death of an unarmed man on an Oakland train platform in a 2009 encounter that set off days of racial rioting in the city.

The jury deliberated more than six hours over two days to convict Johannes Mehserle, who is white, in the killing of 22-year-old Oscar Grant, a black man who was shot to death as he lay face-down.

Involuntary manslaughter carries a sentence of two to four years.

Mehserle was placed in handcuffs and taken away after the verdict. He turned to his family and mouthed, "I love you, guys."

Johannes Mehserle, right, testified that he thought Grant had a weapon. (Cathleen Allison/Associated Press)

At least five bystanders videotaped the New Year's Day incident in what was among the most racially polarizing cases in California since four Los Angeles officers were acquitted in 1992 in the beating of Rodney King.

On the east side of San Francisco Bay, police in riot gear were deployed on the streets of Oakland, fearing protests would erupt following the verdict. Gov. Arnold Schwarzenegger issued a statement urging Californians to remain calm and not resort to violence.

A crowd near Oakland City Hall moaned and cursed when they heard the verdict. A dozen people gathered in a semi-circle to pray.

"It's not real, it's not real. Where's the justice? He was killed in cold blood," said Amber Royal, 23, of Oakland.

Grant family lawyer John Burris said the family was "extremely disappointed" with the verdict.

"This verdict is not a true representation of what happened to Oscar Grant and what happened to him that night. This was not a voluntary manslaughter case," Burris said.

The jury had a choice between murder and lesser charges of voluntary and involuntary manslaughter. The panel included eight women and four men, and none listed their race as black.

Seven said they were white, three were Latino and one was Asian-Pacific. One declined to state their race.

The verdict followed a three-week trial in which prosecutors played videos recorded by bystanders, and witnesses recounted hearing the frightening gunshot that killed Grant.

Mehserle, 28, testified that he struggled with Grant and saw him digging in his pocket as officers responded to reports of a fight at a train station. Fearing Grant could have a weapon, Mehserle said he decided to shock Grant with his Taser but pulled his .40-caliber handgun instead.

Alameda County Deputy District Attorney David Stein said in his closing argument that Mehserle let his emotions get the better of him and intended to shoot Grant with the handgun without justification.

One of Grant's friends, Jackie Bryson, testified that Mehserle said "(expletive) this" before firing the fatal shot.

Defence lawyer Michael Rains contended the shooting was a tragic accident. Mehserle had no motive to shoot Grant, even though he was resisting arrest, the lawyer argued.

Planned to use stun gun

Rains also said Mehserle told a colleague before the shooting: " I can't get his hands. I'm going to tase him."

Mehserle pleaded not guilty to murder and resigned from the Bay Area Rapid Transit agency after the shooting.

Fallout from the shooting was swift in Oakland after the videos were shown on television and the internet. The shooting and the nearly two weeks it took to arrest Mehserle sent the city into a tailspin of violence as downtown businesses were damaged, cars were set ablaze and clashes erupted between protesters and police.

Grant has become a martyr of sorts in a city where more than a third of residents are black. His omnipresent image on buildings and storefront windows arguably rivals that of slain hometown rapper Tupac Shakur.

Grant's family and friends filed multimillion-dollar lawsuits against the transit agency. Only the mother of Grant's daughter has reached a settlement.

Prior to his death, Grant had been released from jail after being sentenced to 16 months for a gun possession charge, filed after he ran from police and was subdued by an officer with a stun gun.