In the second day of Mehserle's preliminary hearing in Alameda County Superior Court, San Francisco State University student Tommy Cross said he thinks that BART officers, particularly Tony Pirone, used excessive force when they responded to the Fruitvale station after receiving reports that there had been a fight on a crowded train.

Cross said Pirone yelled at Grant, a 22-year-old Hayward man, and other passengers to "Get off the train (expletive)" in a "hostile and aggressive tone."

Cross said he decided to record the incident with his camera because he felt Pirone was being too rough with Grant.

"I was wondering why the officer was using so much force and being so aggressive with a man who was cooperative," he said.

His video was played in court Tuesday.

Cross said that after firing the shot that struck grant, Mehserle, 27, said, "Oh my God, oh my God."

Under cross-examination by Mehserle's lawyer, Michael Rains, Cross admitted that he had no idea if Grant had committed a crime, had a gun or was under arrest at the time of the shooting.

Daniel Liu, another passenger on the train, which had departed from San Francisco and was headed toward Dublin, said he also decided to record the incident after he saw Pirone struggling with several passengers.

Liu said Grant appeared to be cooperative and that after Mehserle's gun went off, the expression on Mehserle's face appeared to indicate that "he was surprised and shocked."

Dan Liu, who was the first to provide exclusive video footage of the shooting to KTVU, was the second to testify. In an exclusive interview after Tuesday's testimony, he said that he went through three fake names after the incident during interactions with the press.

"I just didn't want to make a big deal out of it," he said.

Liu said that the memory of the shooting continues to be present in his mind.

"It kept recurring in my mind and my thoughts. It will always be there," he said.

Rains has said that Mehserle meant to use his Taser to subdue Grant and fired his gun by mistake.

Another witness, Jamil Dewar, 16, testified that he, Grant and a large group of their mutual friends had been partying in San Francisco that night.

Dewar said Grant had been drinking but said he doesn't know how much "because I wasn't watching."

Dewar said Grant had gotten into a fight with another man on the train but that he and several other friends had broken up the fight before the train arrived at the Fruitvale station.

Deputy District Attorney David Stein rested the prosecution's case today and Rains will begin presenting witnesses on Mehserle's behalf Wednesday morning.

At the end of Mehserle's preliminary hearing, which is expected to last two weeks, Judge C. Don Clay will determine whether prosecutors have presented enough evidence to have Mehserle ordered to stand trial on murder charges.

The shooting of Oscar Grant was captured on numerous cell phone cameras, and the people who recorded those images figured prominently in the hearing.

Former BART police officer Johannes Mehserle -- out on $3 million bail and wearing a bullet proof vest -- was surrounded by deputies, bodyguards, his attorney and parents as he left an Oakland courtroom Monday.

For four hours, he sat stoically listening to the beginning of a hearing to see if there's enough evidence to try him for murder.

The first witness prosecutors called was Karina Vargas. She repeated what she told KTVU shortly after the New Year's Day shooting: that she didn't know Oscar Grant but turned on her camera because she thought police “were being too rough with him.”

She turned her camera to an arrest at her side and heard a gunshot.

As the tape of the shot played in court, Vargas wiped tears from her eyes. Family members of 22-year-old Oscar Grant, the unarmed man killed by the shot, cried.

"It's very painful but we know it's something we have to go through at this time to get justice for Oscar," said Grant's uncle Bobby Johnson outside the courtroom.

Under cross examination, Vargas said after firing his gun, Mehserle put his hands to his head and “looked dumbfounded and in shock.”

A second woman on BART who also took video said she didn't see that reaction from Mehserle.

While demonstrators rallied outside, inside court the doctor who performed the autopsy on Oscar Grant said the single gunshot entered from the left side of his back and "almost" exited his right chest.

Former officer Mehserle's defense is expected to be that he mistakenly fired his gun instead of his Taser.

The preliminary hearing which continues Tuesday is expected to last two weeks. Then Judge C. Don Clay will decide if there is enough evidence to try Johannese Mersehle for manslaughter or murder for the shooting of Oscar Grant.