A white South Carolina police officer has been charged with murder after video emerged of him shooting a black man running away from him.
State investigators arrested North Charleston police officer Michael Slager on Tuesday after viewing the mobile phone video of the shooting.
Authorities say victim Walter Lamer Scott was shot after the officer had 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, I 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 Mr Scott had been arrested about 10 times, mostly for failing to pay child support or show up for court hearings.
Mr 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.
Dorothy Williams, a Charleston city councillor, told CNN the community had remained calm in this case because Officer Slager was charged so quickly.
US police: Controversial recent killings
April 2015: Walter Lamer Scott, 50, is shot eight times in South Carolina as he runs away from Officer Michael Slager. Mr Scott dies at the scene. The shooting is captured on video and Mr Slager is charged with murder.
December 2014: Jerame Reid, 36, is shot dead during a routine traffic stop in New Jersey. An officer claims Mr Reid was reaching for a gun, but video footage seems to suggest he was attempting to step out of the car, hands raised.
November 2014: Tamir Rice, a 12-year-old boy, is shot dead in a playground by Cleveland police after a local resident reports he is pointing a gun at passers by. The gun turns out to be a toy. A grand jury will decide whether police will face charges.
August 2014: Michael Brown, an unarmed 18-year-old, is shot dead by Officer Darren Wilson in Ferguson, Missouri. The shooting leads to protests, first in Ferguson and later nationwide. A grand jury decides not to charge Mr Wilson.
July 2014: Eric Garner, an asthma sufferer, is stopped by police in New York and placed in a chokehold after refusing to be handcuffed. He dies despite repeatedly telling officers he cannot breathe. No police are charged.
March 2014: James Boyd, an unarmed homeless man camping in Alberquerque, is shot dead by two officers. Video of the incident leads prosecutors to say the officers acted with "deliberate intention" and they are charged.