Los Angeles ? As public outrage mounts, various law enforcement agencies have opened investigations into the arrest of a teenager who was videotaped being slammed onto a police car and punched in the face while he was handcuffed.

Dozens of angry protesters descended on Inglewood City Hall on Tuesday, demanding an end to police brutality and the ouster of Officer Jeremy Morse. Inglewood Mayor Roosevelt Dorn responded by saying that the officer should be fired and charged with assault.

“I will not under any circumstances tolerate the type of conduct I observed in the videotape,” Dorn told a packed City Hall news conference. “In my opinion the district attorney’s office should act.”

Meanwhile, lawyers for 16-year-old Donovan Jackson and his father plan to announce their intent to file a lawsuit Wednesday at the federal courthouse in downtown Los Angeles.

Rep. Maxine Waters sent a letter to Attorney General John Ashcroft demanding an investigation of the altercation, and charged that the white officer’s treatment of the black teen was racially motivated.

The FBI said it has opened a civil rights investigation. The Inglewood Police Department, the Los Angeles County sheriff and district attorney also are investigating.

Morse, a three-year veteran who was put on leave Monday with pay, could not be reached for comment. Phone messages left for the president of the Inglewood Police Officers Association were not immediately returned.

The incident happened during a traffic stop Saturday afternoon just east of Los Angeles International Airport.

A tourist’s videotape showed Morse hoisting Jackson to his feet, throwing his body onto a car, then striking him in the face with a closed fist. Two other officers appear to intervene, with at least one trying to pull away the first officer’s arm.

Police and sheriff’s officials said the teen lunged at deputies and was combative, while the boy’s father, the driver of the car that was stopped, said his son cooperated and Morse attacked him unprovoked. The family’s lawyer, Joe Hopkins, said the teen is developmentally disabled with no arrest record.

The teen was booked for investigation of assault on a peace officer; his father was cited for driving with a suspended license.

The video was recorded by a man who was staying at a motel across the street.

Another person who says he was victimized by Morse has also come forward.

Neilson Williams, 32, claims he was handcuffed and beaten by Morse and other officers June 23. He says he lapsed into a coma and was hospitalized for several days.

Williams alleges the officers gave no explanation for stopping him. He said he has filed a formal complaint with Inglewood police.

Sgt. Ron Ragan said the complaint is confidential and an investigation was being conducted. A police department news release said Williams was belligerent and resisted arrest.