The North Charleston police chief, Eddie Driggers, said officer Slager, 33, had been arrested and charged with murder.
Attorney L Chris Stewart, who came to North Charleston a day after the shooting to represent the family, said the video forced authorities to act quickly and decisively, and he called the person who made the video a hero.
“What happened today doesn’t happen all the time,” Stewart told a news conference. “What if there was no video?” Scott’s mother stood nearby, saying, “Thank you, Lord” and “Hallelujah.”
The family plans to file a civil rights suit against Slager, the department and the city, Stewart said.
Scott’s older brother Anthony told the Post & Courier: “We just would like for justice to be taken, for justice to be served, and we would like for the truth to come out so my brother can rest in peace. Whatever happened yesterday, all we want is the truth, and we will go to any length to get it.”
Anthony Scott said his late sibling served for two years in the US Coast Guard, that he was a father of four, and that he loved the Dallas Cowboys.
According to the Post & Courier, Walter Scott had a warrant out for his arrest from a family court at the time of his death.
His arrest history, mostly for contempt of court charges for failing to pay child support, included one accusation of a violation stemming from an assault and battery charge in 1987, the newspaper reported.
A local Black Lives Matter group, formed after the death of unarmed teenager Michael Brown in Ferguson, Missouri, last August, has planned a demonstration on Wednesday morning at North Charleston city hall.
The Federal Bureau of Investigation and the Justice Department’s Civil Rights Division have also launched investigations into Saturday’s shooting.
“The Department of Justice Civil Rights Division and the South Carolina US 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,” the Justice Department said in a statement.
The murder charges against Slager come amid a national debate on police practice after a spate of high-profile police killings around the country.
President Barack Obama convened a national police taskforce in the wake of the death of Brown in Ferguson, which sparked a wave of unrest in the small city and protests across the country.
The taskforce recommended a variety of criminal justice reforms last month,including that local law enforcement agencies report each officer involved in a shooting to federal government when they occur. At present there are no official national statistics on officers involved in fatalities as local agencies are not required to provide information to the federal government.
Also in South Carolina, a white police officer was charged on Tuesday in the case of a 68-year-old black man who was shot dead last year. A grand jury had earlier chosen to indict North Augusta officer Justin Craven on a charge of misconduct in office, rather than the manslaughter indictment sought by prosecutors, in the February 2014 death of Ernest Satterwhite. The new charge, discharging a gun into an occupied vehicle, is a felony.