(01-14) 19:51 PST OAKLAND -- The unarmed man killed by former BART police Officer Johannes Mehserle on an Oakland train platform early New Year's Day put up a brief struggle with officers but had been restrained and had both arms behind him when he was shot in the back, police investigators said. 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. SOURCE:SFGATE.COM