NORTH CHARLESTON, S.C. — The police officer who was arrested on Tuesday after shooting and killing an unarmed black man has been fired from the department and the police chief here said Wednesday that he was appalled by what a video of the encounter revealed.

“I have watched the video and I was sickened by what I saw,” Eddie Driggers, the North Charleston police chief, told reporters, at an emotional and often chaotic news conference, with protesters repeatedly shouting and interrupting. “And I have not watched it since.”

Asked whether the proper protocols were followed after the shooting, Chief Driggers said, “Obviously not.”

There were pointed questions about when — and if — first-aid was provided to the victim and if the officer’s version of events was ever in doubt before the video emerged. Officials declined to answer those questions, saying they had immediately turned to the state to carry out an impartial and independent investigation.

“That’s the right thing to do,” Chief Driggers said.

As protesters gathered outside City Hall, the mayor of North Charleston, Keith Summey, made clear that he was trying to calm the community. He said he and the chief had visited the family of Walter L. Scott, 50, the man who was fired at eight times as he ran away from an officer after a traffic stop.

“We let them know how we felt about their loss, and how bad it was,” the mayor said, adding that the city would provide a police escort at the funeral.

Mayor Summey said he had issued an executive order that all of the department’s police officers start wearing body cameras — a tacit acknowledgment of the importance video played in this case.

Mr. Scott’s father, in an interview on the “Today” show on NBC earlier in the day, said he believed that without the video, the officer would never have faced prosecution.

“It would have never come to light. They would have swept it under the rug, like they did with many others,” Walter Scott Sr., the father of the victim, said.

The officer, Michael T. Slager, 33, was being held at the Charleston County Jail after a magistrate judge on Tuesday night denied him bond. Officials said at the news conference that the city would continue to cover health insurance for his wife, who is eight months’ pregnant.

During a court appearance conducted by videoconference, Officer Slager, dressed in a jail uniform, appeared nervous and said little beyond disclosing that he was a married father of two stepchildren. He said that he was expecting another child and that he lived near the North Charleston neighborhood where the shooting took place.

A makeshift memorial was taking shape on Wednesday in the empty lot behind Mega Pawn on Rivers Avenue, where Mr.Scott, 50, was shot on Saturday morning. Two small Styrofoam-backed flower wreaths, one with an orange bow and one with white flowers in the shape of a cross, could be seen along with 11 white candles, some lit.

Mr. Scott’s family spoke in a series of nationally televised interviews on Wednesday morning, saying they were glad the truth had come out. They said they were pleased the video had been made public, despite how painful it was to watch.

“When I saw it, I fell to my feet and my heart was broken,” Mr. Scott’s father said.

“The way he was shooting that gun, it looked like he was trying to kill a deer,” Mr. Scott said “I don’t know whether it was racial, or it was something wrong with his head.”

Unlike in many prominent cases involving the use of deadly force by the police, there appeared to be little ambiguity in what took place here. The video showed that Mr. Scott was shot as he ran away from Officer Slager.

The swift action taken by local prosecutors after the video surfaced and the nearly uniform public comments by local politicians condemning the actions of the police officer seem to have helped keep the community calm, even as the incident underscored the tension between the police and minority neighborhoods around the country.

A few dozen people gathered outside City Hall in North Charleston on Wednesday morning to protest police practices in the city, South Carolina’s third largest.

Clutching signs with slogans like “the whole world is watching” and “back turned, don’t shoot,” protesters talked about Mr. Scott’s death and a broader distrust of the authorities here.

”This has been a reality that has been in the North Charleston Police Department for many, many years,” a man said over a loudspeaker. “It just so happens we got a video.”

Demonstrator after demonstrator stepped to the microphones to share accounts of what they said was systemic racism. Some spoke of groundless searches, while others complained about arrests for nonviolent offenses.

The protest was vocal, but peaceful. A few law enforcement officials, dressed in plain clothes, stood nearby, and Sheriff Al Cannon of Charleston County walked through the crowd at one point.

From Ferguson, Mo., to Staten Island, New York, recent fatal confrontations between police officers and black men have set off widespread protests and outrage. President Obama dispatched Attorney General Eric H. Holder Jr. to cities around the country in an effort to improve police relations with minority neighborhoods.

But the death of two police officers in New York City, shot and killed by a mentally disturbed young man who said he was targeting the police to avenge the shooting of Michael Brown in Ferguson, raised concerns that the national discussion had turned into something much darker.

As the video of the shooting in North Charleston played over and over on screens across the nation, there was little debate about whether the use of force was justified.

Instead, the question was what would have happened if not for the video.

Before the video surfaced, immediately after the shooting, the State Law Enforcement Division started an investigation to determine whether the officer’s action was justified.

The shooting unfolded after Officer Slager stopped the driver of a Mercedes-Benz with a broken taillight, according to police reports.

As soon as he stopped the car, the driver, Mr. Scott, fled and Officer Slager chased him into a grassy lot that abuts a muffler shop. The officer fired his Taser, a stun gun, but it did not stop Mr. Scott, according to police reports.

A video taken by a bystander shows what happened next. Wires, which carry the electrical current from the stun gun, appear to be extending from Mr. Scott’s body as he tussled with Officer Slager. As Mr. Scott turns to run, something — it is not clear whether it is the stun gun — is either tossed or knocked to the ground behind the two men.

Officer Slager draws his gun as Mr. Scott is running away. When the officer fires, Mr. Scott appears to be 15 to 20 feet away and fleeing. He falls after the last of eight shots.

The officer then goes back toward where the initial scuffle occurred and picks something up off the ground. Moments later, he drops an object near Mr. Scott’s body, the video shows.

Mr. Scott was shot on an unkempt grassy lot, about the size of a football field. Tall trees with hanging Spanish moss shade most of the lawn.

Even after Mr. Scott was shot and lay, motionless on the ground, Officer Slager placed his hands behind his back and handcuffed him. It would be several more minutes, according to the video, before an officer with a medical kit arrived to perform first aid.