The four men are being held at the Hennepin County jail and have yet to be charged.

The day after the shooting, Mr. Scarsella posted a Confederate banner known as the Bonnie Blue Flag at the top of his Facebook page. A video posted on YouTube showed a SWAT team arresting him at his house in a Minneapolis suburb later in the day.

The racial tension at the protests began to grow after a video was posted online last week showing two light-skinned men saying they planned to go to the protest to “make the fire rise.”

In the video, which was posted on a Black Lives Matter Facebook page to alert members, two young men in masks and military fatigues were driving in a car. The driver identified himself as SaigaMarine, and his passenger as BlackPowerRanger.

“We’re locked and loaded,” SaigaMarine told the camera as he brandished a pistol. Referring to protesters using a racial slur, he said the pair planned to visit the protest to “do a little bit of reverse cultural enriching.”