The Alameda County District Attorney's Office said it filed murder charges against a former Bay Area transit officer in the shooting death of an unarmed black man.

District Attorney Tom Orloff said the murder charge was filed against 27-year-old Johannes Mehserle because the evidence indicates "an unlawful killing done by an intentional act" and that there was no evidence available yet that could "mitigate" that.

Oakland police said Wednesday that Mehserle was arrested in Douglas County, Nevada on Tuesday in connection with the shooting of Oscar Grant III at the Fruitvale BART station in Oakland on Jan. 1.

Officers said Mehserle waived an extradition hearing in Nevada, and is being transported to the Santa Rita Jail in Dublin.

"This investigation shows that no one is above the law, but everyone is entitled to due process of the law," said BART Board President Thomas Blalock said. "BART investigated this shooting thoroughly and treated the investigation and information no differently because the suspect involved was a police officer. Now we have to let due process take its course."

Orloff said Mehserle could be arraigned as early as Thursday.

Nevada authorities arrested Mehserle after learning the Alameda County District Attorney's Office had issued a warrant for his arrest for homicide, according to the Douglas County Sheriff's Office.

Oakland police provided the sheriff's office information Tuesday morning that Mehserle was in the Zephyr Cove area of Lake Tahoe, Nev., the sheriff's office reported.

After receiving confirmation that an arrest warrant had been issued, authorities contacted Mehserle's attorney, who in turn called Mehserle.

Mehserle left a home at 1007 Skyland Drive in Zephyr Cove and surrendered to sheriff's officials without incident at about 6:20 p.m., the sheriff's office reported.

"We want the public to know that this one incident is not reflective of BART, its police or its employees," BART General Manager Dorothy Dugger said. "I have great confidence in the professionalism of the BART Police Department. This was a tragic event in which a life was lost for which someone has been arrested and charged."

He was booked into the Douglas County Sheriff's Office main jail in Minden, according to the sheriff's office.

He had been kept in a segregated area of the facility and is on a precautionary health and welfare watch, according to the sheriff's office.

The shooting at the Fruitvale station in Oakland occurred shortly after 2 a.m. on Jan. 1 when Mehserle and other officers stopped a train at the station in Oakland after receiving reports that two groups of men were fighting on the train.

The shooting, which is under investigation by multiple agencies, has prompted protests in the Bay Area, including a violent demonstration last week in Oakland.

Another protest is scheduled for 4 p.m. today outside Oakland's City Hall.