The Wisconsin Department of Justice has just thoroughly destroyed the "white police officer kills innocent, unarmed black man" narrative that has led to rioting in Kenosha all week.
Jacob Blake either lunged for his knife or had it in his hand and lunged for what officer reasonably thought was another weapon.
He was not "breaking up a fight between two women." His girlfriend called 911 because Blake wasn't supposed to be at her home. He is charged with sexually assaulting her and had an outstanding arrest warrant for it.
He was violent from the outset of the encounter and officers tried Tazing him. It didn't work. Blake gave officers reason to believe he was armed, and they can be heard yelling "drop the knife" as he walks toward a car full of children.
Blake clearly has something that looks like a curved blade in his hand as he walks toward the car, having just fought officers and terrified his girlfriend. He opens the door and lunges for something (either the knife or what the officer reasonably feared was another weapon) 
