SAN FRANCISCO — A white former transit police officer accused of killing an unarmed black man on an Oakland train platform has been arrested on a murder warrant in Nevada, 12 days after the shooting inflamed long-running tensions between police and many African-American residents.

Johannes Mehserle, 27, was in custody Tuesday evening under a fugitive warrant issued from California, law enforcement officials said.

The 27-year-old Mehserle surrendered without incident, authorities said.

Karen Boyd, a spokeswoman for Oakland Mayor Ron Dellums, confirmed the arrest and said the mayor's office had been informed of it earlier Tuesday night. Alameda County District Attorney Tom Orloff was expected to announce details of the charges on Wednesday.

A message left late Tuesday night at the office of Mehserle's attorney, Christopher Miller, was not immediately returned. But he told the San Francisco Chronicle that Mehserle was arrested on suspicion of murder.

Witnesses say Mehserle fired into the back of 22-year-old Oscar Grant while the man was lying facedown on a train platform at a station in Oakland. Grant and others had been pulled off a train after reports of fighting, as New Year's Eve revelers were shuttling home after midnight.

The shooting was captured on several cell phone cameras and widely viewed on the Internet. Hundreds of protesters have taken to the streets calling for the prosecution of Mehserle, with one rally last Wednesday spiraling into violence and resulting in more than 100 arrests and dozens of businesses damaged.

John Burris, the attorney for Grant's family, said he talked to Grant's mother, Wanda Johnson, on Tuesday night and she was delighted with the news of the arrest.

"However it does not bring her son back," Burris said. "But she is happy and pleased that an arrest has occurred."

Grant's family has also filed a $25 million legal claim against Bay Area Rapid Transit.

Dereca Blackmon, the co-founder of the Coalition Against Police Execution, which was organizing a protest Wednesday, said she was pleased Mehserle was arrested but still wanted to know more details.

"We're disappointed that it took him fleeing the state in order for the law to take some action," she said. "Honestly this situation brings more questions than answers. Why was he fleeing?"

Douglas County, where the arrest occurred, is 15 miles south of Carson City in northwestern Nevada and includes Lake Tahoe and Carson Valley.

Mehserle refused to talk to BART investigators before resigning his position last week. The transit authority passed on details of its internal investigation to Orloff's office on Monday. The case also is being investigated by the Oakland Police Department.

State Attorney General Jerry Brown has assigned a prosecutor to monitor the case, and the U.S. Department of Justice has dispatched mediators to help avert violent protests such as one in Oakland last week.

BART board member Carole Ward Allen said she was pleased to hear the news about the arrest.

"I want to know why he did it," she said. "We've heard from everybody else but him. While I can't speak for the entire BART board, we want to make this process as transparent as possible."

The San Francisco Chronicle first reported the arrest.