The case against defendant Johannes Mehserle has provoked racial unrest at every turn, and police in Oakland, the scene of the killing, were on alert for more problems following a sentence many thought was too light.
"This is outrageous - This sentence of two years is outrageous," one protester told CBS Station KPIX. "For murder, for killing somebody!"
A rally billed as a tribute to Oscar Grant turned into a march through the downtown area, where people broke car windows and two windows on a bus. After police in riot gear repeatedly blocked and outflanked them, several hundred protesters splintered into smaller groups and entered residential neighborhoods.
Police helicopters hovered above, shining spotlights on the crowd.
A group of about 100 protesters holding a banner reading "Justice for Oscar Grant" was hemmed in with officers on both sides of the street before police started making arrests around 8 p.m. Friday, saying the assembly was illegal.
The action was taken, Oakland Police Chief Anthony Batts said, after one officer had his gun taken from him in a fight and another officer was hit by a car and suffered what police described as a non-life-threatening injury. "It's one thing breaking windows; it's another thing taking a gun from an officer," the chief said.
Police spokesman Jeff Thomason said officers checking the backpacks of several of those arrested found hammers, pepper spray, switchblades and anti-freeze.
Mehserle's sentence, handed down in Los Angeles, also angered the victim's family and friends, who demanded a much harsher punishment.
Wanda Johnson, Grant's mother, shouted, "Oh my!" when Superior Court Judge Robert Perry issued the two-year sentence. She burst out of the courtroom saying, "He got nothing! He got nothing!"
Grant's uncle, Bobby Cephus Johnson, said outside court: "I do believe it's a racist criminal justice system."
Still, he said the family was reacting calmly but added he could not comment for others.
"I have no power over what people feel their matter of expression should be," he said.
Some of the dozens of people who gathered outside Oakland City Hall for a tribute to victim Oscar Grant broke into tears when they learned of the judge's decision. Outside the Los Angeles courthouse, a small crowd that had earlier shouted "No justice, no peace" reacted relatively calmly to the sentence.
Mehserle, 28, had faced a possible 14-year maximum term after being convicted of involuntary manslaughter. At the time of the shooting, Mehserle was a Bay Area Rapid Transit officer responding to a report of a fight.
In making his decision during the highly charged, 3½-hour hearing, Perry threw out a gun enhancement that could have added as much as 10 years in prison and said there was overwhelming evidence that it was an accidental shooting.
Perry said race would not factor into his decision and although Mehserle had shown "tons of remorse" for killing Grant, he would have to account that a "young man needlessly died."
"I did the best I could with this case," Perry told the courtroom. "My decisions today will not be well-received by many people. I'm sorry for that."
Police said they were prepared in case there was a replay of the rioting in Oakland that followed the shooting on New Year's Day 2009.
Mayor Ron Dellums said he understood the pain and disappointment sparked by the sentence.
"It is still my hope that people will express their anger, will express their disappointment, their outrage, their pain in a manner that is nonviolent, in a manner that is not destructive to our community," he said at a news conference.
Johnson family attorney John Burris acknowledged a small step was taken by the justice system in sentencing Mehserle to two years, but he said that was insufficient. Both Burris and Bobby Johnson noted that NFL star Michael Vick got a harsher sentence for running a dog-fighting ring.
"What you take from that is that Oscar Grant's life was not worth very much," Burris said.
He also targeted Perry's comments before sentencing that he was saddened by the polarization of the community over the shooting.
"This case does nothing at all to heal, if that was ever any intent," Burris said.
Reaction to the case has drawn comparisons to the infamous 1991 Rodney King beating by Los Angeles police officers, which inflamed a racial divide and led to the disastrous 1992 riot when the officers were acquitted of brutality charges.
Mehserle was convicted in July in the videotaped killing of Grant, 22, in Oakland. The case was moved to Los Angeles for trial.
Perry had wide discretion when sentencing Mehserle. Prosecutors sought prison time while defense lawyers argued for probation. The judge gave Mehserle the minimum possible prison sentence.
Defense attorney Michael Rains immediately filed an appeal with the court after the sentencing. After time already served and good behavior credits, Mehserle will likely serve an additional six to seven months based on California's sentencing guidelines, the lawyer said.
Mehserle testified during the trial that he thought Grant had a weapon and decided to shock him with his stun gun but instead pulled his .40-caliber handgun. Grant was unarmed and face down when he was shot.
Sentencing came after four relatives of Grant and his fiancee pleaded with Perry to send Mehserle to prison for 14 years.
Wanda Johnson cried and struggled to give a victim impact statement. She said she regrets telling her son to take a BART train to San Francisco before the shooting.
"I live every day of my life in pain," she said. "My son is not here because of a careless action."
The family continues to maintain that it was murder when Mehserle shot Grant.
Mehserle, shackled and wearing a jail jumpsuit, also stood before the judge before sentencing and apologized for the shooting, which he contended was accidental and not racially motivated.
"I want to say how deeply sorry I am," Mehserle said. "Nothing I ever say or do will heal the wound. I will always be sorry for taking Mr. Grant from them."
He cried during portions of his 10-minute statement and said he and his family have received numerous death threats and he's been "green-lighted" - a term in which other jail inmates have the go-ahead to kill someone.
Earlier, the judge said he had received more than 1,000 letters urging a harsh sentence.
Prosecutors had sought a second-degree murder conviction, saying Mehserle became angry at Grant for resisting arrest.
However, jurors were given the choice of lesser charges, including voluntary and involuntary manslaughter. In reaching a decision on involuntary manslaughter, jurors found that Mehserle didn't mean to kill Grant, but his behavior was still so negligent that it was criminal.
Involuntary manslaughter has a sentencing range of two to four years, while the gun allegation carries a term of three, four or 10 years.
The judge rebuked prosecutors for arguing that Mehserle intentionally shot Grant, saying there wasn't any evidence to back up that allegation. Perry also said he believed the videos showed Grant resisted arrest and many people, including Mehserle's fellow officers and Grant's friends, contributed to the tragedy.
"All of these people share some responsibility," Perry said.
Early in the day, before the sentencing, there was a scuffle outside the Los Angeles courthouse that led to at least one arrest and an undercover officer being briefly handcuffed.
Police Lt. John Romero said the undercover police officer was coming out of the building when a member of the crowd recognized him and the two had a verbal exchange. When it escalated to pushing and shoving among the crowd, sheriff's deputies who guard the building moved in.