WASHINGTON (AFP) - The bystander who shot a video, apparently showing a white police officer fatally shooting an unarmed black man, said he knew right away the profound significance of the chilling footage he had recorded.

"As you can see in the video, the police officer just shot him in the back," said Mr Feidin Santana, who used his cellphone to film the dramatic and tragic encounter. "I knew right away, I had something on my hands," he told NBC television.

As a result of the recording which in just 24 hours has been seen around the world, the police officer, 33-year-old Michael Slager, was charged with murder on Tuesday, and could face a sentence of up to life in prison or the death penalty.

Slager stands accused of shooting Mr Walter Scott, 50, repeatedly in the back after a scuffle that began with a traffic stop for a broken tail light in North Charleston, South Carolina.

Mr Santana said that after filming the incident, he immediately became fearful of his own safety.

"I won't deny I knew the magnitude of this, and I even thought about erasing the video," the 23-year old said in a separate interview with MSNBC television.

"I felt that my life with this information might be in some danger. I thought about erasing the video and getting out of the community, leaving North Charleston," he said.

In the video, Mr Scott is seen being shot as he tried to run from Slager, who then handcuffs the dying man.

"It's not something that no one can feel happy about. He has his family, Mr Scott also has his family," Mr Santana - who was on his way to work when he noticed Slager and Mr Scott, and heard a stun gun being deployed - told NBC.

"But I think, you know, (the officer) made a bad decision, and you pay for your decisions in this life."

"Mr Scott didn't deserve this," he continued. "And there were other ways that can be used to get him arrested. And that wasn't the proper way to do that."

He described the scene that unfolded during the fatal encounter.

"Before I started recording, they were down on the floor. I remember the police (officer) had control of the situation," Mr Santana said.

"He had control of Scott. And Scott was trying just to get away from the Taser (stun gun). But like I said, he never used the Taser against the cop."

Several killings of unarmed black men by police officers in recent months have sparked sometimes violent protests across the United States, with demonstrators alleging racism in the nation's police departments.

Officers have rarely been charged in the shootings, however - even when the incidents were recorded.

Slager was arrested and charged with murder after the video surfaced showing him shooting eight times at Mr Scott, 50, while Mr Scott was running away.

He was fired from the police force on Wednesday after being charged with murder and being booked into jail.

Slager could face a sentence of up to life in prison or the death penalty.

Mayor Keith Summey announced the sacking at a highly charged press conference frequently interrupted by residents angered over the killing.

The mayor said the police department would buy body cameras for officers to wear to help investigate shootings.

Protesters gathered in front of City Hall throughout the day Wednesday and demonstrated against racial inequality.

Signs at the rally included slogans such as: "Stop racist police terror" and "No justice, no peace".

Some demonstrators said the quick arrest of the officer helped defuse what could have been a tense situation.

The deadly shooting occurred on Saturday following a traffic stop for a broken tail light. After initial police reports claimed Mr Scott had taken Slager's stun gun, Mr Santana's video was released to The New York Times and published on Tuesday.

The video shows wires from the stun gun extending from Mr Scott's body, implying that the victim rather than the police officer had been hit as the two men scuffled.

As Mr Scott, who was heavy-set, tries to flee, Slager draws his handgun and shoots eight times toward his back.

The officer later approaches Mr Scott, who is on the ground, telling him to put his hands behind his back, before putting him in handcuffs.

Slager appears to pick up a device that had fallen during the altercation and drop it by Mr Scott's body.

Mr Scott was hit by five bullets - three times in the back, once in the upper buttocks and once in the ear, said family lawyer Chris Stewart, quoting the coroner who examined Scott's body, according to the Times.

Mr Scott's father, also named Walter, said the family was devastated by his son's death, but was grateful for the video evidence.

"The way he was shooting that gun, it looked like he was trying to kill a deer or something running through the woods. I don't know whether it was racial or something wrong with his head or what," the father told NBC's Today Show.

"I thank God they had the video. God has my back. When I saw it, my heart was broken. I said, 'It can't be.' I saw it. I couldn't take it anymore."

The victim's family spoke out at a news conference after the officer's arrest and called the unidentified person who filmed the video a hero.

They remembered Mr Scott as a Dallas Cowboys football fan and loving father of four.

Senator Lindsey Graham of South Carolina expressed his dismay after seeing the video.

"The horrific video is very difficult to watch and deeply troubling on many fronts," Mr Graham said.

The US Justice Department released a statement saying it would "take appropriate action" over the shooting.

The killing of unarmed black teen Michael Brown in August was a catalyst for a recent surge in protests and a renewed debate on racism and police tactics.

A jury chose not to indict a Ferguson, Missouri, police officer for the shooting. Since then, other killings by police have prompted protests in cities from coast to coast.

In December, two New York police officers were killed by a gunman who had boasted he was going to avenge police abuses.

Police officers have enjoyed significant legal leeway in the United States and prosecutors and civilian grand juries have often proved reluctant to indict them over excessive force.

The US Justice Department has launched investigations into a number of police departments after shootings.

It unearthed what it called damning evidence of racism in the Ferguson police force after Brown's shooting.