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Former Bay Area Rapid Transit police officer Johannes Mehserle. (AP Photo/Cathleen Allison, File)

LOS ANGELES — Chaos, distrust and disorder.

That was the theme a prosecutor used Thursday to describe the events that led to the death of Oscar Grant III at the hands of a BART police officer Jan. 1, 2009.

Police aggression and emotions caused the chaos, distrust and disorder that led former BART police Officer Johannes Mehserle to purposely pull out his gun, point it at Grant's back and fatally shoot the 22-year-old Hayward man, deputy district attorney David Stein said.

"The shooting of Oscar Grant was the result of emotions taking over. It was the result of aggression taking over for training and discipline," Stein said during a 95-minute opening statement. "Was the defendant confused? Look at where he is looking. He is looking at what he is doing."

Stein then showed one of six videos that recorded Grant's death and paused it at the second Mehserle looks down to his right hip and begins to pull out his gun.

Stein focused on the videos captured by cameras and cell phones of passengers on the train. He also showed the jury new videos created by the Alameda County District Attorney's Office that demonstrate the differences between what Mehserle had to do to remove his gun from its holster and what he would have needed to do to access his Taser.

"It only comes out when you want it to come out," Stein said, explaining the various snaps and buttons an officer must push to remove a gun from a holster.

But the Taser holster, Stein said as he held it before the jury, "doesn't have the same retention device."

Stein also pointed out that Mehserle wore his Taser and gun on opposite sides of his body and showed the jury that the gun is black and heavier than the Taser, which is yellow and lighter.

Stein began his opening statement in front of the packed courtroom of Los Angeles Superior Court Judge Robert Perry. About 45 people watched, including media members from the Bay Area and Los Angeles. Also in the galley were Grant's family members, including his mother, Wanda Johnson, and Alameda County District Attorney Nancy O'Malley, who inherited the controversial murder case when longtime District Attorney Tom Orloff retired last year.

Through much of his opening statements, Stein focused on the actions of former BART Officer Anthony Pirone, who appears in almost all the videos to incite the crowd on the BART train and Grant and his friends through physical and verbal abuse.

Stein called it an example of out-of-control police officers who acted out of aggression instead of according to their training.

"What happens when an officer or a group of officers believe that their duty is to more than just protect and serve?" Stein asked, using a motto he said was created by the Los Angeles Police Department. "What happens when they believe they should punish? "... The result will always be chaos, distrust and disorder."

That disorder led to Mehserle's pulling out his gun, shooting Grant and then immediately telling Pirone, " 'Tony, I thought he was going for his gun,' " Stein said.

"You'll see for yourselves that Mr. Grant wasn't resisting," Stein said. "He was in the process of putting his hands behind his back offering himself up for arrest."

While Stein displayed what at times was chaos on the platform and highlighted the constant foul language and aggression used by Pirone, Mehserle's defense attorney Michael Rains appeared less emotional as he addressed the jury.

Rains, in part, placed blame on BART for the shooting, citing minimal training of officers in the use of Tasers and what Rains suggested was a substandard policy for equipping officers with the device.

And, Rains said, Stein was correct when pointing out that, at times, Pirone appeared to not act professionally. However, Rains said, Pirone was not on trial.

"Mr. Stein didn't spend that much time talking about Mr. Mehserle," Rains said.

That's because, Rains said, Mehserle was on the train platform for only 2½ minutes before he fired a shot into Grant's back.

While Rains agreed Pirone's language was not professional, he said the aggression Pirone showed was provoked by Grant and his friends, who Rains said tried to strike blows at the officers.

Ultimately, the content of the videos will be left up to the jury to interpret. But Rains and Stein each suggested the videos will show different things happening — with Stein saying they will show police aggression and Rains saying they will show suspects resisting arrest.

Rains said the videos show Mehserle acting calm and in control.

"He is in complete control for the entire 2½ minutes until the fatal shot is fired," Rains said of Mehserle. "He had no beef with Oscar Grant. He had no animosity with Oscar Grant."

Rains said Mehserle made a mistake caused by a lack of training in the use of Tasers and has resulted in the 28-year-old already living in a prison.

"For the rest of his life, (Mehserle) will be trapped in a wretched prison of his own memories," Rains said.

Rains said that a frame-by-frame analysis of certain videos will prove that Mehserle struggled to remove his gun from its holster because he believed he was trying to grab his Taser.

"Mehserle is tugging on his gun, he is tugging on his gun with such force," Rains said. "The gun won't come out because he is using the wrong movement."

That frame-by-frame analysis of the video also shows, Rains said, that Mehserle had a look of shock on his face once he fired his gun, then quickly put his hands to his head and leaned over.

"He is sick to his stomach and wants to vomit because he's just shot a man that he did not want to shoot," Rains said.

In a chaotic situation when an officer's stress level is at its peak, an officer no longer thinks about what he is doing and reacts on the training he has been provided, Rains said. Because Mehserle had only six hours of training using a Taser, he became confused and believed his gun was his Taser, Rains said.

"Our brains don't have a dummy light to come on in stressful situations," Rains said. "We are blind to the things happening right in front of us."

Rains also, for the first time, gave the jury and the public more personal information about Mehserle in what appears an attempt to humanize him for the jury. Rains talked about how Mehserle was born in Germany and ended up in Napa at age 4 when his family moved there.

He said Mehserle won the "most huggable" award in high school and after graduation went to college to study computer programming before he changed his mind and enrolled in a police academy.

Rains spent about two hours giving his opening statements, after which three witnesses were called to the stand. The first witness was a video technician from the District Attorney's Office who explained how she transferred videos of the shooting to a computer.

The other two witnesses were riders on the BART train who captured the killing on their digital cameras.

Also Thursday, a white female juror was excused from the jury and replaced by a Latino woman, leaving the court with five alternates for the remainder of the trial. It is unknown why the juror was excused.