A former Bay Area Rapid Transit officer accused of killing a man at an Oakland train station testified Friday that he mistakenly grabbed his handgun instead of his Taser while trying to subdue the man.

"I thought it was my Taser,'' Johannes Mehserle, 28, said during his trial in downtown Los Angeles.

Mehserle, who is white, is charged with murder for the New Year's Day 2009 shooting of 22-year-old Oscar Grant, who was black. The racially charged case was moved to Los Angeles for trial due to extensive publicity in the Bay Area.

Testifying in his own defense, Mehserle described for jurors his struggle with Grant, saying he was standing over the man trying to handcuff him. Mehserle said Grant was on his knees then fell to the ground.

"My main focus was his hands,'' Mehserle said. "I was trying to get him handcuffed,'' but "his right hand was underneath him.''

He said he was "repeatedly telling him to give me his hand.

At that point, however, Mehserle saw Grant reach into his right pocket, he testified. Mehserle told jurors he had been involved in past cases when people carried small handguns in their pockets.

"I remember the digging motion with his right hand, like he was looking for something,'' Mehserle said. "I made the decision at that point to Tase him.

"... It made me question what his intentions were. I knew the right front pocket was where people kept guns.''

Mehserle said he told Grant he was gong to Taser him, after which Mehserle stood up and backed away from Grant and reached for the Taser. He said he didn't realize he was grabbing his gun instead of the Taser.

He said he wound up firing one shot.

"I remember the pop,'' the ex-transit officer said. "It wasn't very loud. It wasn't like a gunshot -- and I remember thinking the (Taser) had malfunctioned.''

Mehserle said at that point, he looked down, "and saw I had my gun in my hand. It shouldn't have been there.''

He added that he heard Grant say, "You shot me.''

During his testimony, Mehserle appeared to be fighting back tears, prompting a spectator in the courtroom to stand up and shout, "Save those tears, dude'' -- drawing applause from Grant's relatives.

As the man was walking out of the courtroom, Superior Court Judge Robert J. Perry ordered him arrested, and sheriff's deputies took the man into custody.

After sending the jury out of the room, Perry warned the audience that if there were any further outbursts, "I'll clear the courtroom -- press, everyone. I'm not gonna have it.''

Mehserle described his reaction to having fired the shot as "disbelief -- not knowing how or why it could happen.''

He said he remembered looking down, "and I could see there was blood on my hands.''

"Mr. Grant's blood?'' his attorney, Michael L. Rains, asked.

"Yes,'' he answered.

The ex-officer said he was "devastated'' by the events of that day.

"I didn't intend to shoot Mr. Grant,'' he said.

Questioned by Alameda County Deputy District Attorney David R. Stein, the defendant said that from the moment he arrived at the Bart station that night, he had attempted to "de-escalate'' an atmosphere of increasing violence.      A disturbance had been reported on a train, and the shooting occurred as BART officers tried to control a trainload of revelers on a platform.

Images of the shooting, recorded on multiple cameras, were repeatedly broadcast in the Bay Area.

Seeing the videos, Mehserle said Friday, are "like reliving the whole thing over again.''

One of the most bizarre pieces of evidence in the case is a photo of Mehserle taken by Grant on his cell phone moments before he was killed, showing the officer standing over him.