via WGNO:

BATON ROUGE, La. -- (WGNO) -- The graphic video shows a deadly encounter outside a convenience store.

Two police officers pin down Alton Sterling, a 37-year-old black man, then shoot him as he lies on the ground.

The video, shared widely on social media, quickly sparked local protests and drew national attention.

WARNING: Graphic video

Baton Rouge, Louisiana, police say they came to the scene early Tuesday after an anonymous 911 caller reported a man threatening him with a gun.

Accounts of what happened next depend on whom you ask.

Sterling is dead. Federal authorities are investigating. And the president of the NAACP's local branch is calling for the city's police chief and mayor to resign.

The U.S. Justice Department's Civil Rights Division will be the lead agency investigating the shooting, Louisiana Gov. John Bel Edwards told reporters Wednesday. The U.S. attorney's office in Baton Rouge, the FBI and state police also will be involved, he said.

The governor, who called for calm and unity, said he has "very serious concerns" after watching the cell phone video of the shooting.

"The video is disturbing to say the least," Edwards said.

Edmond Jordan, an attorney representing Sterling's family, said the video of the shooting raises troubling questions.

"I think that the city is going to have to give us some good answers," Jordan, who is also a Louisiana state legislator, told CNN. "And I don't know if they'll be able to."

Sterling's family, he said, has seen the video of the shooting.

"(They) are taking it hard right now ... overwhelmed with grief," he said.

FULL STORY: Deadly officer-involved shooting captured on graphic cellphone video - WGNO