GRAPHIC CONTENT WARNING: New video emerges showing killing of Alton Sterling

In a swift move by authorities to keep tensions from boiling over, the U.S. Justice Department has launched a civil rights investigation into the video-recorded killing of a black man who was shot as he scuffled with two white police officers on the pavement outside a convenience store in Baton Rouge, La.

Alton Sterling, 37, was shot and killed by police early Tuesday in the parking lot outside the Triple S Food Mart, where he regularly sold homemade CDs from a folding table.

alton sterling

Alton Sterling, 37, of Baton Rouge, died Tuesday of multiple gunshot wounds after an altercation with police outside a convenience store. (Facebook )

The incident was captured on at least two videos, setting off angry protests in the city's black community. It comes at a time when law enforcement officers across the U.S. are under close scrutiny over what some see as indiscriminate use of deadly force against blacks.

The second cellphone video, taken by the store's owner, Abdullah Muflahi, emerged Wednesday evening. It shows the shooting from a slightly different angle than the widely circulated clip taken by a community activist, as well as a few seconds of footage after shots were fired.

Muflahi's video shows the officers on top of Sterling and the shots being fired. The camera moves away at one point and when it returns, Sterling can be seen lying on the ground with what appears to be blood on his chest.

One officer is lying on the ground on his side with his weapon pointed toward Sterling, who appears to still be alive as his arm moves up to his chest. A voice can be heard saying "Shots fired! Shots fired!" The video then shows a second officer reaching into Sterling's pocket and pulling out an object.

Warning: This video, taken by the store's owner, contains disturbing images and graphic language.

WARNING: Graphic content and explicit language in 2nd video of police-involved shooting in Baton Rouge, La.0:38

Muflahi said he saw Sterling being thrown on top of a car hood. He said Sterling appeared confused and kept asking: "What did I do wrong?"

He said he never saw Sterling with a gun but saw a police officer pull a gun out of Sterling's pocket afterward.

'Very serious concerns'

Moving quickly, just one day after the shooting, Louisiana Gov. John Bel Edwards asked the Justice Department to take the lead in the investigation.

"I have very serious concerns. The video is disturbing, to say the least," the governor said at a news conference.

Edwards said he hoped the public would be patient as the investigation unfolded to avoid "violent acts and the destruction of property," a reference to protests that broke out in Ferguson, Mo., and Baltimore in the past two years after the deaths of Michael Brown and Freddie Gray respectively following deadly police interactions.

Police Shooting-Louisiana

Nishka Johnson touches a makeshift memorial for Alton Sterling, who was shot and killed by Baton Rouge police early Tuesday outside a convenience store where he was selling CDs. (Gerald Herbert/Associated Press)

Edwards said he spoke by phone to express his condolences to Sandra Sterling, an aunt of the victim who was Alton Sterling's primary caregiver while he was growing up.

"It's a horrible thing. It's a horrible thing to happen to him," Sandra Sterling said to media early Wednesday morning. "He didn't deserve that."

Baton Rouge Police Chief Carl Dabadie Jr. has said that Sterling was armed — he didn't specify the type of weapon — but that there are still questions about what happened.

"Like you, there is a lot that we do not understand. And at this point, like you, I am demanding answers," Dabadie said, calling the shooting a "horrible tragedy."

Police said they also have dash-cam video, body-cam video and store surveillance video of the shooting.

Lawyer for Alton Sterling's family speaks about shooting6:31

Sterling was confronted by police after an anonymous caller reported being threatened by someone with gun outside the Triple S Food Mart, authorities said.

The police chief identified the officers involved as Blane Salamoni, a four-year member of the department and Howie Lake II, who has been on the force for three years. Both are currently on administrative leave.

Authorities would not say whether one or both fired their weapons or how many times.

According to court records, Sterling has multiple criminal convictions since the mid-1990s, for battery, resisting arrest, burglary and other crimes. He is a registered sex offender after spending close to four years in prison for felony carnal knowledge of a juvenile.

Protests at shooting scene

In the wake of Sterling's death, hundreds protested Tuesday night, and demonstrators gathered again on Wednesday, shouting slogans and holding up signs.

A makeshift memorial at the scene included notes to "Big Alton."

​"No justice, no peace," chanted the protesters, who occasionally blocked traffic.

Police Shooting Louisiana

Regina Adams, who said she knew Alton Sterling since he was a baby, speaks out as people gather outside the Triple S convenience store in Baton Rouge, La., on Wednesday. (Gerald Herbert/Associated Press)

Quinyetta McMillon, the mother of Sterling's teenage son, trembled as she read a statement outside city hall, where a few dozen protesters and community leaders had assembled. Her son, Cameron, 15, broke down in tears and was led away sobbing as his mother spoke.

She described Sterling as "a man who simply tried to earn a living to take care of his children."

"The individuals involved in his murder took away a man with children who depended upon their daddy on a daily basis," she said.

A cousin of Sterling's, Sharida Sterling, said he had been selling music there for about six years, often lugging his box of CDs, table and folding chair on two buses to get to the store.

Sharida Sterling said that the store management never had any problems with him but that he was often harassed by police — she suspected because he was black and a "big guy."

"I don't want them to get away with a slap on the wrist because it could happen to somebody else's brother," she said.

Investigations often take months

Baton Rouge, a city of about 229,000, is 54 per cent black, according to census data, and more than 25 per cent of its people live in poverty.

The U.S. Justice Department will look into whether the officers wilfully violated Sterling's civil rights through the use of unreasonable or excessive force.

Similar investigations, which often take many months, were opened after Michael Brown's shooting in Ferguson, Mo., and following Eric Garner's chokehold death in New York City.

Federal investigators must meet a high legal burden to bring a civil rights prosecution, establishing that an officer knowingly used unreasonable force under the circumstances and did not simply make a mistake or use poor judgment.

Edmond Jordan, a lawyer for the Sterling family, told CBC News Network that he was "pleased" an investigation was called so quickly.

"Frankly, I credit the people of Baton Rouge, who decided to protest and say they're not going to tolerate this anymore. Because if not for them, and the person who released this video … maybe we wouldn't be at this point."

Warning: This video, taken by a community activist, contains disturbing images

U.S. police shooting caught on camera0:27

With files from CBC News and Reuters