Here's a CNN interview with Piaget Crenshaw who filmed the aftermath and saw the event from her balcony.
She says
"From my point of view I couldn't tell exactly what was going on but it just looked as if he was tryin' to pull him, almost, into the car - and Brown being a bigger fella that didn't seem to have been working, and so of course he got away and that just seemed to have upset the officer. The officer got out and just started chasin' after the boy and I'm hearing shots fired, clearly none of them hit him but one I think did graze him as they said on the autopsy report, and at the end he just turned around after I'm guessing he felt the bullet graze his arm he turned around and then was shot multiple times."
She's giving this commentary on it after so much info has already come out. She's heard Dorian's version which had the "officer tried to pull Mike into the vehicle" and she's parroting that, she's incorporating the autopsy info and trying to make it fit in the way most favorable to Brown, etc.
With regard to this smaller officer trying to pull a 6'4" 293lb man into his cruiser through the window, no thinking person believes that was what the officer was doing. Keep in mind, anything relevant that was going on between them at that point would not have been very apparent to anyone other than Brown and the officer. From the perspective of people outside the vehicle, especially at a distance, they just see Brown leaning into the window and some sort of struggle happening. If they sympathize with Brown (especially with hindsight since he ends up dead shortly) they wish to interpret it as the exceptionally silly "Officer was trying to pull him through the window" but in reality, it seems much more likely, especially if the Officer has the documented and serious head injuries we're hearing about... that Brown leaned into the window to attack the officer and to try to get control of his weapon.
My guess would be that the officer tries to exit his vehicle to have a more proper and serious contact with the two suspects after hearing about the robbery and seeing them holding the box of cigarillos. As he tries to exit the vehicle, Brown isn't having it and shoves the door closed on him, possibly pinching the officer's arm and/or leg at this time, or possibly just pushing the officer back in somewhat. Police protocol would dictate at this time the officer should draw his weapon. Mike Brown then sees the officer drawing his weapon, and rather than doing the smart thing of apologizing for his violence and surrendering, making it clear to the officer he will present no further problem, he instead escalates the violence and leans through the window to attack the officer, and try to gain control of his gun. I have little doubt that if Brown had successfully gotten control of the gun, he would've shot the officer several times through the cruiser window, and then ran off.
So again, I consider the "trying to pull him through the window" thing to just be a silly attempt on the part of Johnson and others outside to make sense of what they were seeing in a way that fits their biases. Why would brown even be up next to the window in the first place if he and Johnson thought the encounter was over after the earlier contact, and the officer was trying to exit the vehicle? The officer wouldn't have beckoned him over to come right next to the door. I believe Brown came right over to the door to prevent the officer's exit, and to attack him.
As for what happened after the officer got out of the vehicle, now in full control of his weapon, and followed after Brown? Who knows. Things were happening very fast at that point, and people inclined to side with Brown watching from various distances may not have noticed something threatening he did.
Frankly, I don't really care what Brown did at that point. If it was a situation where he'd just attacked a police officer unprovoked, injured his face significantly, and tried to take his firearm... I have no problem at all with Wilson getting out and "executing" Brown. That is the expected result after trying to kill a police officer.
I think it's a result he could have avoided even then by halting, and completely complying - putting his hands up, making no further movement either away from or toward the officer, and kneeling, etc. I'm not sure how much in the way of orders Wilson was giving at that point, and how obvious Brown was making it that he wouldn't obey orders... but we've heard he may have at least said "freeze!" which sounds like he was still willing to spare Brown if Brown would comply.
Seems like Brown didn't comply, and/or did something threatening.
I'd be fine with it even if he'd unloaded into Brown's back. The man had just tried to kill a police officer. That makes him a credible threat to the community at large if allowed to escape, IMO.