The case will be centered around what happen when he started to run, that's it. Nothing that happen before hand matters. The cops life wasn't in danger when the guy was running from him. Thats why this video is soooooooooooo important. There is no reasonable doubt. The case starts when he ran.
the guy who filmed the video is a witness who will surely be put on stand to testify about what he saw prior to recording, and that was some sort of altercation, the video starts when he ran but the defense attorneys will center on the events (scuffle) leading up to the flight from officer.
This is what's important about the witness not saying a fukking word. Everything leading up to the shooting will be used in his defense. Him vaguely saying there was a scuffle leaves plenty of doubt... this is why you don't fukking talk to these people. It's never beneficial to talk to the media or the police.