The ejection port is on the right side of Darren Wilson's service pistol. As a result, any discharge of the firearm from inside the car would put the shell towards the front windshield and bounce around in the car. If it were to exit the vehicle at all, it would have lost most of its velocity and thus roll to a stop somewhere quite close to the truck, which one of them did. Are you going to sit there and say that a shell casing leapt from the gun in the opposite direction of where it came to rest, escaped being obstructed by three bodies, and landed all the way on the other side of the road? Sorry man, that is a bridge too far for me. Give me a possible reason. The only one I can think of is the casing might have landed in Officer Wilson's lap and when he got out of the car, it rolled over there. However, unless he literally jumped out of the car and did a pelvic thrust towards the sidewalk, I don't see how a little shell casing is going to make it through the rough asphalt and come to rest on the other side of the road. Simply disclaiming that shell casings are unpredictable does not explain the fact that one landed impossibly far away from the vehicle. As far as I know, they are still subject to the laws of physics.

"Are any of these things likely to have had any material affect on the investigation?" I think the answer is "No"

We don't know what might have been washed off. It is possible that his hands were drenched in Mike Brown's blood, which would support Johnson's account that he was trying to pull Mike Brown into the car. The bottom line is that this is pretty fucking basic procedure. Unless you think that police officers should be allowed to bag and tag their own guns and wash their hands after they kill an unarmed citizen? Furthermore, no notes or recordings taken of the initial statement? And then they all ride to the hospital together? Come on now... I'm willing to grant that there is the possibility for human error, but this shit is just ridiculous.

We know Darren Wilson knew about the robbery suspects because we have a recording of him responding to the dispatcher about it. Even if Wilson didn't know all the details that went over the radio, he knew it was two individuals who had stolen cigars.

We know Darren Wilson knew about the robbery, and presumably, knew that there were suspects in the world that allegedly committed the crime. However, not knowing the details is the crucial piece. To him, Dorian Johnson and Mike Brown were just two black kids in the middle of the road, which brings me to my next point.

"Put me on Canfield with two and send me another car,” what he is telling the dispatcher is that he is on Canfield with two individuals who are possible suspects and he needs another car.

Ferguson police specifically target black people in the community for jaywalking. That is also in the report. I think that if Officer Wilson legitimately thought Mike Brown and Dorian Johnson were suspects in this robbery, he would not have approached them before backup arrived. He was initially going to stop them for jaywalking, which I am assuming would not require immediate backup. My guess is he planned on searching them during the course of the interaction, which is another Ferguson police custom, so he needed backup at some point, just not right away. I don't think we can assume that he knew with any degree of certainty that these two individuals were specifically involved in the robbery. Perhaps he had an inkling in his mind that it was a possibility, but his actions do not support the way police officers handle strong-arm robbers.

You're forgetting he still has to come to a halt from running, turn around, scrunch his hands, etc.

If Brown stopped running and turned around after being hit by the first round (as Dorian Johnson's account suggests), then took another two bullets to the interior right bicep and right shoulder, he would have been facing Officer Wilson when the pause occurred. The final volley landed the two fatal rounds in the eye and head. If the only thing to do is stagger, not stop and turn around, a guy who is 6'5" could easily stagger seven steps in three-ish seconds (I am assuming that the three second pause was between the last shot of the first volley and the first shot of the last volley, not that the final volley only lasted three seconds total).

The report explains why it finds some witnesses credible and others not credible.

A major part of the reason why the contractor's account was dismissed is because the contractor insisted there were three officers present during the shooting. As far as I can tell, the guy that saw Officer Wilson pull out a Taser that didn't exist also basically suffers from whatever makes the account the contractor gave unreliable. The reason this witness is credible is pretty clearly because he supports the police narrative that Mike Brown charged Officer Wilson. Nearly the entire rest of his testimony is ridiculous.

I don't know if the police supervisor was able to remember with 100% clarity what Wilson said at the crime scene.

This is why it is so fucked up that there were no notes or recordings taken of the initial statement.

The direct testimony we have from Wilson is that he drew the gun first--which is actually a worse story for him (if he was lying) than if Brown grabbed the gun. But it doesn't matter, because a police officer is entitled to at least draw his gun if he is being pummeled.

You are incorrect. Brown reaching for the gun establishes Officer Wilson's reasonable fear for his life. If Brown did not reach for the gun before Officer Wilson drew, we have to rely on Officer Wilson's testimony that he was in fear for his life based on what the pictures of his alleged injuries showed. Now, you tell me, does that look like a fight that could have ended in death? He reasonably thought that his life was going to end based on what looks like a fuckin slap fight?

Lastly, drawing a firearm that you don't intend to use is asking for it to be used against you. That is the cardinal rule of defensive firearm training. If Officer Wilson really and truly believed he was going to die, he would have put the truck in drive and floored it.