A six-minute video showed Tabatabainejad audibly screaming in pain as he was stunned several times with a Taser, each time for three to five seconds. He was told repeatedly to stand up and stop fighting, and was told that if he did not do so he would "get Tased again."

Tabatabainejad was also stunned with the Taser when he was already handcuffed, said Carlos Zaragoza, a third-year English and history student who witnessed the incident.

"(He was) no possible danger to any of the police," Zaragoza said. "(He was) getting shocked and Tasered as he was handcuffed."

But Young said at the time the police likely had no way of knowing whether the individual was armed or that he was a student.

As Tabatabainejad was being dragged through the room by two officers, he repeated in a strained scream, "I'm not fighting you" and "I said I would leave."

The officers used the "drive stun" setting in the Taser, which delivers a shock to a specific part of the body with the front of the Taser, Young said.

A Taser delivers volts of low-amperage energy to the body, causing a disruption of the body's electrical energy pulses and locking the muscles, according to a report by the American Civil Liberties Union.

"It's an electrical shock. ... It causes pain," Young said, adding that the drive stun would not likely demobilize a person or cause residual pain after the shock was administered. Young also said a Taser is less forceful than a baton, for example.

But according to a study published in the Lancet Medical Journal in 2001, a charge of three to five seconds can result in immobilization for five to 15 minutes, which would mean that Tabatabainejad could have been physically unable to stand when the officers demanded that he do so.

When Tabatabainejad, 23, refused to provide his ID to the community service officer, the officer told him he would have to show it or leave the library, the report said.

After repeated requests, the officer left and returned with campus police, who asked Tabatabainejad to leave "multiple times," according to a statement by the UCLA Police Department.

"He continued to refuse," the statement said. "As the officers attempted to escort him out, he went limp and continued to refuse to cooperate with officers or leave the building."

Witnesses disputed that account, saying that when campus police arrived, Tabatabainejad had begun to walk toward the door with his backpack. When an officer approached him and grabbed his arm, the witnesses said, Tabatabainejad told the officer to let go, yelling "Get off me" several times.

"Tabatabainejad encouraged library patrons to join his resistance," police said. "The officers deemed it necessary to use the Taser."

Officers stunned Tabatabainejad, causing him to fall to the floor.

The video shows Tabatabainejad yelling, "Here's your Patriot Act, here's your ... abuse of power," the Daily Bruin reported, adding he used a profanity.

"It was beyond grotesque," said UCLA graduate David Remesnitsky of Los Angeles, who witnessed the incident. "By the end they took him over the stairs, lifted him up and Tasered him on his rear end. It seemed like it was inappropriately placed. The Tasering was so unnecessary and they just kept doing it."

Campus police confirmed that Tabatabainejad was stunned "multiple" times.

By then, Remesnitsky said, a crowd of 50 or 60 had gathered and were shouting at the officers to stop and demanding their names and badge numbers.

Remesnitsky said officers told him to leave or he would be Tasered.

Tabatabainejad declined to comment. He was arrested Tuesday night and cited by campus police for resisting and obstructing a police officer and was released.