On July 5, two white Baton Rouge police officers fatally shot 37-year-old black man Alton Sterling. Here's what you need to know. (Monica Akhtar/The Washington Post)

AGAIN.

Again, a black man has been shot to death by a white police officer or officers. Again, the incident has been recorded on a cellphone camera. Again, the available evidence — not conclusive, but persuasive — suggests the shooting was unwarranted.

Americans once again are watching the shuddering images of a man’s death in horror, in disbelief, in indignation. Demonstrators, mainly African American, fueled by a potent sense of injustice, once again are chanting in the streets.

The dead man this time is Alton Sterling, 37, who was selling CDs in front of a convenience store in Baton Rouge early Tuesday morning when police arrived, alerted by an anonymous phone call reporting that a man had brandished a gun. The video of the ensuing encounter, recorded by a witness, shows one officer tackling Mr. Sterling with help from a second, a brief struggle on the ground and someone shouting, “He’s got a gun! Gun!” And then the sickening sound of shots, along with gasps and cries of witnesses as the camera falls away.

We don’t know if Mr. Sterling, whose chest and back were pierced by bullets, had a gun. If he did, we don’t know if he reached for it. We can’t tell whether he was actively resisting the officers, or why they tackled him in the first place.

What we do know is that the images of the incident, which are partially obstructed by a car, do not suggest the police had lost physical control of Mr. Sterling at any time. Nor do they appear to show that the police faced an imminent threat to their safety or lives that would justify opening fire. One witness said he saw a gun taken from Mr. Sterling’s pocket after he was shot.

Louisiana Gov. John Bel Edwards (D) was wise to immediately hand the investigation of Mr. Sterling’s death to the Justice Department’s Civil Rights Division, along with federal prosecutors in Louisiana and the FBI. That may reassure protesters distrustful of local authorities’ ability or inclination to investigate their own city’s police force — all the more given that one of the officers in the video is the son of a captain in charge of special operations in the same department.

There are questions that federal investigators should ask immediately: What other video footage exists — from the officers’ cruiser or body cameras, the convenience store’s surveillance cameras or other witnesses — and what does it show? Did Mr. Sterling in fact have a gun? And was he the man who had brandished one in the alleged incident to which the officers were responding in the first place?

What is known, in the words of Quinyetta McMillon, the mother of Mr. Sterling’s oldest son, is that the incident “took away a man with children who depended upon their daddy on a daily basis.” As she said that, their son, who is 15, sobbed at her side.