The conclusion by Oakland police, contained in a legal filing made public Wednesday, contributed to Alameda County prosecutors' decision to charge Mehserle, 27, with murdering 22-year-old Oscar Grant of Hayward.

It was an extraordinary decision. Several legal experts said they could recall no instance of a police officer in California being charged with murder for an on-duty incident, and Alameda County District Attorney Tom Orloff said he had never brought such a case in his 14 years on the job.

But the circumstances of the case are equally extraordinary, in that the shooting was filmed by several BART passengers and Mehserle has refused to talk to investigators about why he shot Grant. Orloff said Wednesday that both factors played into his decision to charge Mehserle with murder.

Mehserle waived extradition in a court hearing in Douglas County, Nev., on Wednesday, a day after he was arrested at a friend's home near Lake Tahoe, where his attorney said he had gone after receiving death threats in the Bay Area.

The Lafayette resident was driven to the Santa Rita Jail in Dublin, where he was placed in "protective custody," sheriff's Sgt. J.D. Nelson said. He is scheduled to be arraigned today in Oakland.

His attorney, Christopher Miller, said he expects Mehserle to be cleared. The former officer was not available for an interview.

Orloff said Mehserle had committed murder because he killed Grant in an intentional, unlawful act. Orloff said no evidence his office reviewed - witness statements and video shot by BART passengers, including footage that the public has not yet seen but that the district attorney called "very helpful" - indicated the shooting was justified.

Grant was shot at the Fruitvale BART Station about 2 a.m. Jan. 1 after he and several other young men were pulled off a train by police investigating reports of a fight. In a court filing justifying Mehserle's arrest, an Oakland police sergeant said video footage showed that "a struggle ensued" between Grant and two BART officers, including Mehserle.

Both hands behind back

The filing adds that the other officer was holding Grant down on his stomach, with his knee on Grant's head and neck. Mehserle was "seen trying to pull Grant's right arm, which appeared to be underneath Grant's body," before abruptly shooting him, police said.

"After careful analysis of the video, it is clear that both Grant's hands were behind his back, a position hands are commonly placed in by police officers in order to handcuff individuals," the police filing said. It concluded that Grant had been "restrained and unarmed" when he was shot.

Mehserle's subsequent refusal to talk to detectives about the shooting, Orloff said, left authorities with no window into his state of mind.

"When you basically have a situation of an unlawful, intentional killing of one individual by another, and that's all you know - and that's really all we know in this case - then that's a murder," the district attorney said at an Oakland news conference.

Mehserle's silence, Orloff said, "made it more difficult in the sense that his statement could or could not have given me some insight into his thought process, and I didn't have that insight. The videos are very powerful on what act was committed. The issue likely to be in this case is, what was the mental state at the time that act was committed?"

Miller, Mehserle's attorney, said at a news conference later in Sacramento that his client was "a fine young man" and an excellent police officer. Miller declined to say why Mehserle shot Grant.

The officer resigned from the BART police force Jan. 7 rather than talk to internal affairs inspectors who could have built a disciplinary case against him.

"As the 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.

Grant family pleased

Grant's family members were pleased by the murder charge, said their attorney, John Burris, who has filed a $25 million legal claim against BART. He said he doubted the shooting would have led to charges if it had not been caught on video.

"Anything less than murder would not have been satisfying," Burris said.

He quoted Grant's mother, Wanda Johnson, as saying, "That's very good, but it doesn't bring my son back."

Although more than 100 people are killed by police officers each year in California, officers are rarely charged with serious crimes. Several law enforcement officials and experts said Wednesday they could not recall the last time a California police officer was charged with murder after an on-duty incident.

"It hasn't been studied," said Bob Stresak, a spokesman for the California Commission on Peace Officer Standards and Training. "The occurrence of that is so rare, there's not a lot to study."

Some Oakland civic and community leaders have called for charges against the other BART officers who were on the Fruitvale Station platform when Grant was shot, but Orloff said he had found no evidence to justify such an action.

Sources said the other officers - including Tony Pirone, the officer whose knee was on Grant's head - remained on paid administrative leave Wednesday. BART Police Chief Gary Gee, appearing with Orloff at the Oakland news conference, said none of them was the subject of internal affairs investigations.

Orloff said he expected the case against Mehserle to go to trial, where a jury would probably have the option of convicting the former officer of first- or second-degree murder; convicting him of a lesser charge of voluntary or involuntary manslaughter; or acquitting him. Orloff said he would fight any defense effort to move the case out of Alameda County.

Not considered flight risk

Mehserle appeared stoic Wednesday morning as he was brought into a courtroom in Minden, Nev., southeast of Lake Tahoe. Wearing a navy-blue jail jumpsuit and shackles on his hands and feet, he told Judge Paul Gilbert, "I'd like to waive extradition." The hearing lasted about five minutes.

Mehserle was arrested Tuesday evening at a friend's home in the Zephyr Cove area near Lake Tahoe, authorities said. Orloff said Oakland police had used "technology" to track him and did not suspect him of trying to flee.

"There was no effort whatsoever to avoid arrest," defense attorney Miller said. "He took his family up there to avoid the pressures of what was going on in the Bay Area. As you're all aware, there were significant death threats made against him and his family."

Grant's death has been seen by some community leaders and activists as symbolic of problems between police and young men of color and as a test of whether officers can be held accountable for alleged brutality. Mehserle is white, and Grant was black.

Chief Gee said Wednesday that the investigation had found no "nexus to race that provoked this to happen."

BART board member Lynette Sweet, who called for Gee and BART General Manager Dorothy Dugger to lose their jobs because of how the initial investigation was handled, called the arrest "a great start."

"I just hope that this is for real," Sweet said. "Let's hope it's not a farce. No matter how this plays out, I just hope that justice is served. All eyes will be watching."

Demian Bulwa reported from Oakland, Wyatt Buchanan from Sacramento and Matthew Yi from Minden, Nev. Chronicle staff writers Rachel Gordon, Christopher Heredia, Henry K. Lee and Kevin Fagan contributed to this report. E-mail the writers at myi@sfchronicle.com, dbulwa@sfchronicle.com and wbuchanan@sfchronicle.com.

This article appeared on page A - 1 of the San Francisco Chronicle