– The fatal shooting of a black man running from a white police officer exacerbated the nation's debate over police use of force Wednesday, and the mayor and police chief of South Carolina's third-largest city said they were "sickened" by what a bystander's video revealed.

The officer, who has been charged with murder, was fired, and the mayor said he ordered enough body cameras for every officer on the street. But that did little to quell the outrage of an angry crowd at North Charleston's City Hall, and the officials were shouted down by protesters calling for justice.

The officer reported that he fired in self-defense after the suspect he pulled over Saturday for a broken brake light grabbed his stun gun. Police shared his version with the public and pledged a full investigation.

But the officer's story quickly unraveled after a nervous bystander's shaky video was shared with the dead man's family and then the world.

It shows Patrolman Michael Slager firing repeatedly at Walter Scott as the unarmed 50-year-old tries to flee. The video begins with what appears to be a brief physical altercation over the officer's Taser, which falls to the ground shortly before the officer pulls out his Glock pistol and fires eight times. Scott then crumples to the ground about 30 feet away. Not once can the officer be heard yelling "stop" or telling the man to surrender.

Moments later, the officer is seen walking back and picking up what appears to be the Taser, then returning to drop it at Scott's feet as another officer arrives to check the man's condition.

The video changed everything, authorities and advocates said Wednesday.

"What if there was no video? What if there was no witness, or 'hero' as I call him, to come forward?" said L. Chris Stewart, a lawyer for the dead man's family. "We didn't know he existed. He came out the blue."

Slager was promptly abandoned by his attorney and charged with murder after the video was made public by the slain man's family.

Mayor Keith Summey announced that the officer was immediately fired and that he's ordering 150 more body cameras, so that every uniformed officer on the street will wear one, a key demand of the Black Lives Matter movement that is growing nationwide.

"I have watched the video. And I was sickened by what I saw. And I have not watched it since," Police Chief Eddie Driggers said.

The news conference was meant to quiet the uproar, but both the mayor and chief were interrupted by chants of "no justice, no peace."

Outside City Hall, local organizer Muhiydin D'Baha repeatedly hollered, "Eight shots in the back!" through a bullhorn. The crowd yelled, "In the back!" in response, aiming to coin a new phrase to supplant the "hands up, don't shoot!" refrain that grew out of other officer-involved killings.

Scott's family and Stewart appealed to keep protests peaceful, saying the murder charge shows the system is working in this case so far.

But Stewart does plan to sue police, and said officials acted decisively only because of the video, which was recorded by a whispering man who tried to avoid the officers' attention as he peered over a chain-link fence into the empty lot where Scott died.

That man, Fayden Santana, told NBC on Wednesday that he approached the scene because he noticed Slager controlling Scott. "The police had control of the situation," Santana said. "He had control of Scott. And Scott was trying just to get away from the Taser."

Local police turned over the investigation to state law enforcement. The video also prompted the FBI and the Justice Department's civil rights prosecutors to announce a federal probe.