SANTA ANA (CBS) — “Dad – they’re killing me!”

Kelly Thomas, a mentally ill, homeless man from Fullerton, yelled that out during a violent struggle with police. He died days later from his wounds.

In court Monday, people gasped, screamed and some cried as they watched a video of the beating, which was captured on a security camera at a Fullerton bus station.

On the night of July 5, 2011, Fullerton Police Officer Manuel Ramos was responding to a call of a car break-in and found 37-year-old Kelly Thomas walking near the scene of the crime. He began questioning the homeless man and called for back-up.

“Put your hands on your (expletive) knees…put your feet out in front of you,” Ramos could be seen telling Thomas in the video.

“Well, which one is it, dude?” Thomas said.

“Both,” Ramos responded.

“I can’t do both,” Thomas retorted.

“Well, you’re gonna have to learn real quick,” Ramos told him.

According to audio captured on an officer’s tape recorder, the situation escalated quickly after that.

Ramos and Officer Joseph Wolfe questioned Thomas about someone else’s mail in his backpack.

After a few orders, Ramos told Thomas with an expletive how he’s going to use his fists on him. The two exchange expletives, Thomas gets up and the batons come out.

“Get on the ground,” an officer yelled.

The courtroom audience gasped at what they saw next – officers began swinging their batons at Thomas and piling on top of him.

Thomas could be heard apologizing to officers – “OK, I’m sorry.”

After repeatedly ordering Thomas to put his hands behind his back another officer knees Thomas.

“OK man, I can’t breathe,” Thomas said.

Minutes later, another officer, Corporal Jay Cicinelli, ordered Thomas to stop resisting. Then, he used his Taser on Thomas several times.

Thomas could be heard screaming and begging the officers to stop.

As the officers continue to struggle with Thomas the man screams out for his father, crying for help.

Thomas’ father, Ron, was in the courtroom Monday. This was not the first time he’s seen this video and he sat calmly through the showing.

As four officers subdued Thomas, one striked the schizophrenic man repeatedly.

After the struggle, Cicinelli can be heard telling another officer he believed Thomas was on something.

“We ran out of options so I got the end of my Taser and I probably…I just started smashing his face to hell,” Cicinelli said.

KCAL9 News spoke with Steve Meister, a criminal defense attorney and former L.A. County prosecutor, and Timothy Williams Jr, a police procedures expert and former LAPD detective, about the video and how it will impact the case.

“Look how many officers it took for him to stay still – five,” Meister remarked while watching the video. “An unmedicated schizo who was obviously capable to fight 5 officers who are trained to take down… That presents a danger.”

“In my opinion, all of this was excessive force,” Williams said. “I’ve been in altercations and I know it doesn’t take all that to control someone who was unarmed.”

“Even though charges are about how this ended, the case is about how it started,” Meister said.

He added that, if there is a trial, the video will be presented in two different ways: first, showing officers in a dangerous situation, and, on the flipside, officers over-reacting.