The witness turned the camera phone away as the second officer took his gun and pointed it at Sterling.
Audio has recorded what sounds like five gunshots. Sterling died at the scene.
Sterling was selling CDs outside the Triple S Food Mart, at the corner of Fairfields Avenue and North Foster Drive, WAFB-TV reports.
Police said that officers went to the Triple S Food Mart to reports of a man who was selling CDs threatening someone with a gun.
Baton Rouge Police have released few details about the shooting, including whether Sterling was armed.
A witness, the store's owner, Abdullah Muflahi, told the Advocate Sterling was armed, but was not holding his gun or touching his pockets during the incident. The gun was later found in his pocket, Muflahi told the newspaper.
The brief video shows the end of the incident. An officer can be heard yelling "get on the ground," out of the view of the camera. As the camera pans up, an officer is seen charging at Sterling, grabbing him and tackling him into the hood of a car and then down to the pavement.
Another officer can then be seen kneeling on Sterling. After a few seconds one of the officers yells, "He's got a gun!" The officer seen in the video kneeling on Sterling draws his weapon and one of them says, "if you f*cking move, I swear to God!"
Two shots can then be heard and the bystander drops the cell phone. Three more shots are then fired after a brief pause.
Sterling was shot multiple times in the chest and back, the Baton Rouge Coroner's Office told WAFB.
Two officers, who have not been identified, have been placed on administrative leave.
Body cameras worn by the officers apparently came loose during the incident Baton Rouge police spokesman Cpl. L'Jean McKneely said.
Police said in addition to the witness video, there is dashcam video and surveillance video from the convenience store.
Baton Rouge Mayor Kip Holden has said there will be a thorough investigation.
"This is not going to be a cover up," Holden said.
Mignon Chambers, Sterling's sister, told WAFB-TV that he was a father of five who has been selling CDs outside the store for years.
"I really wanna know more about what happened, about the whole situation, because my brother didn't deserve it. He didn't deserve it at all," Chambers told the news station.
