Updated

A former transit police officer has been charged with murder for the fatal shooting of an unarmed and allegedly restrained black man in a racially charged case that has outraged residents and community leaders and set off violent protests.

Newly released court documents allege that Johannes Mehserle, who was charged Tuesday, shot 22-year-old Oscar Grant while Grant had his hands behind his back and another officer was kneeling on his neck.

Alameda County District Attorney Tom Orloff made the rare decision to file a murder charge against a police officer for an on-duty incident.

"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's nothing that would mitigate that to something lower than a murder," Orloff said at a news conference. He said he would not speculate on whether the charge would end up being first-degree murder or second-degree murder.

Witnesses said Grant was lying face down on a train platform at a station in Oakland when the 27-year-old white officer shot him in the back. Grant and others had been pulled off a train after reports of fighting, as New Year's Eve revelers were shuttling home after midnight.

Allegations that Grant's hands were behind his back and another officer was kneeling on him were contained in an Oakland police officer's request to issue an arrest warrant. It said it appeared from cell phone video that "Mehserle shot and killed Oscar Grant while Grant was restrained and unarmed."

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The shooting, captured on cell phone cameras and widely viewed on the Internet, has inflamed long-running tensions in Oakland between law enforcement authorities and many African-American residents.

Hundreds of people have taken to the streets calling for the prosecution of Mehserle, with one rally last week spiraling into violence that resulted in more than 100 arrests and damage to dozens of businesses.

More than a thousand demonstrators again gathered Wednesday, outside Oakland City Hall. They listened to preachers, community activists and others who urged a peaceful demonstration and demanded justice for Grant. Some protesters wore "Don't Shoot" signs on their backs and held signs that said, "Silence the Violence."

The protest was mostly peaceful before a small group went on a window-breaking rampage through downtown, smashing windows at several businesses and about 30 cars. Eighteen people were arrested, mostly for vandalism, Oakland police spokesman Jeff Thomason said.

Mehserle surrendered without incident Tuesday at a family friend's house in an upscale neighborhood on the east shore of Lake Tahoe in Douglas County, Nev., law enforcement officials said.

During a brief court appearance in Minden, Nev., on Wednesday, he waived extradition and was returned to California to face charges. His lawyer, Christopher Miller, said his client had been in Nevada for a few days to get away from the pressures of what was happening in the Bay Area, and there was no effort to avoid arrest.

"As you are all aware there were some death threats, significant death threats, made against him and his family," he said.

Late Wednesday, about 50 people were evacuated from their homes after Mehserle's parents found two suspicious packages on their porch. When authorities could not determine what was inside the packages, they destroyed them.

Mehserle could be arraigned as early as Thursday, Miller said.

"As this case moves forward through the justice system and all of the circumstances of that chaotic night become clear, I fully expect Mr. Mehserle will be cleared of the charges against him," Miller said. He called Mehserle "a fine officer with an excellent work history" who had been on the force about two years.

John Burris, the attorney for Grant's family, said the news of the charge was "terrific."

"It is consistent with the evidence I have seen. I think the family will be pleased," Burris said.

Michael Rains, a former police officer who has represented cops as a lawyer since 1979, called such a charge "extremely rare." Rains said he knows of no similar prosecutions in Northern California in the 45 years he has been either a police officer or a lawyer.

Rains said that convicting a police officer of murder for firing a weapon while on duty could prove difficult. He said there are many laws and Supreme Court cases to "discourage second-guessing and hindsighting of their actions." Rains also said that juries typically view police officers favorably.

"Police officers usually have a leg up in the jury box going to trial," Rains said.

According to the Oakland police department, no officer-involved shootings since 2004 resulted in a firing or criminal charges against the officers. A number of investigations from 2008 remain unresolved.

Grant was the first person killed by Bay Area Rapid Transit police since 2001, when a 42-year-old man was shot at a station in the nearby city of Hayward, officials said. The earlier shooting was deemed justifiable.

A message left with the BART Police Officers Association was not immediately returned Wednesday.

BART Board President Thomas Blalock said in a statement that the investigation "shows that no one is above the law, but everyone is entitled to due process of the law."

Click here for more on this story from KTVU-TV in San Francisco.