Johnson made a few claims that can be dis-proven, thereby negating his whole testimony.
For one, the cop is bruised, meaning that Brown did more than just suffer a neck grab like Johnson said. He was probably holding the door shut on the officer's head.
Do we really think the officer pulled up so close to them that he could not open his door without hitting them, (bad form for a cop) like Johnson says, or was he several feet away, ( good form for a cop) getting out of the car, when Brown slammed it on him?
If there are no entry wounds to the back, all those witnesses that claim he was shot in the back are lying too, Johnson included. Dump there testimony.
Hmm, I wonder if skinned knees would mean Brown was charging forward when he went down? Vs stationary, hands up, would crumple straight down? The body position seems consistent with a charge, head towards the cop car.
The location of the spent shells can tell pretty good where the officer was when he fired. If there was one that indicated the cop had advance, then retreated while still firing, that might mean he was being charged by a wounded bull.
So it seems to me there is potential evidence to mean we can not trust the "eye witnesses".
Likewise, the same evidence can corroborate stories- including the officer's.