White police officer charged over unarmed black man's death

State investigators arrested North Charleston police officer Michael Slager on Tuesday after viewing a video of the shooting.

Authorities say the victim, Walter Lamer Scott, was shot after the officer already targeted him with a stun gun.

The US Department of Justice is set to launch an investigation.

"When you're wrong, you're wrong," North Charleston Mayor Keith Summey said, announcing the arrest. "When you make a bad decision, don't care if you're behind the shield or a citizen on the street, you have to live with that decision."

Police officers in the US fatally shoot and kill hundreds of people each year, but only a handful of cases result in the officer facing criminal charges.

The incident on Saturday began after Scott's car was stopped for having a broken rear light, local media reported.

A video of the incident published by the New York Times shows a brief scuffle before Scott begins running away. The video then shows the officer firing several shots at Scott, who falls to the ground.

The Post and Courier newspaper of Charleston reported that Scott had been arrested about 10 times, mostly for failing to pay child support or show up for court hearings.

Scott's brother, Anthony, told the Post and Courier that he believed his brother fled from Mr Slager because he owed child support.

Anthony Scott said that because of the video, "we have received the truth" and "through the process, justice has been served".

Chris Stewart, a lawyer for Scott's family, called the passer-by who recorded the video a "hero".

The shooting occurred as heightened scrutiny is being placed on police officer shootings, particularly those that involve white officers and unarmed black suspects.

A grand jury declined to indict Ferguson, Missouri officer Darren Wilson over the fatal shooting of Michael Brown last August, leading to nationwide protests.