US South Carolina shooting
North Charleston police officer Michael Slager is seen in an undated photo released by the Charleston County Sheriff's Office in Charleston Heights, South CarolinaHandout/Reuters

A US police officer in South Carolina has been formally charged with murder for shooting down an unarmed black man who appeared to be fleeing.

Michael Slager, a 33-year-old white officer, was seen firing eight bullets at 50-year-old Walter Scott as he was running away.

Investigators have arrested the officer who was with the North Charleston Police Department and formally charged him with murder on 7 April. If convicted, the officer could face up to life in prison or a death sentence.

A video, thought to be shot by an anonymous bystander, was also obtained by the New York Times showing the exact shooting incident, which took place on 4 April. The police officer was arrested after the release of the video footage.

"I can tell you that as the result of that video and the bad decision made by our officer, he will be charged with murder. When you're wrong, you're wrong. And if you make a bad decision -- don't care if you're behind the shield or just a citizen on the street -- you have to live by that decision," North Charleston Mayor Keith Summey told reporters.

Slager is believed to have shot dead Scott even after he was targeting him with a stun gun. Scott was pulled over for a traffic stop.

Slager's lawyer initially released a statement saying the police officer "followed all the proper procedures and policies of the North Charleston police department".

An investigation led by the Federal Bureau of Investigation and the Justice Department's Civil Rights Division has also been launched.

"The Department of Justice Civil Rights Division and the South Carolina U.S. Attorney's Office will work with the FBI in the investigation. The Department of Justice will take appropriate action in light of the evidence and developments in the state case," said the Department.

The fatal incident marks a remarkable shift in the US justice system as the police officer involved in the matter was charged swiftly. Though hundreds of people have been killed by security personnel every year in the US, criminal proceedings against officers take place only in a few cases.