First off, the video looks bad and like BMoZ I think it deserves to be investigated and run through the courts as it may well have been a bad shoot. I think the cop unwisely went to guns while simultaneously trying to grapple with the fleeing driver and pulling the trigger was a mistake at best. That said, a lot of the claims that he is a liar or that the other cops at the scene were lying liars are really a matter of definition and degree rather than outright fabrication.
Isn't there also dash cam footage 
From the early body cam footage it doesn't look like the car was equipped with one. Check out 0:16 in the full body cam video below.
He got himself tangled in the car 
The cop could easily provide a legally defensible explanation of why he felt the need to reach into the car (preventing someone from fleeing a traffic stop) even if it was - in retrospect - the wrong move to make. If a police officer steps in front of a stopped vehicle to try to prevent it from fleeing, the driver would still be liable if they hit the cop, right? Seems to be a similar case here. The cop did something that put himself in danger but only because the driver was refusing to comply and was attempting to rabbit.
Pulling the gun at the same time as reaching into the car was a bad decision.
Just consider where the officer is standing when he fires the fatal shot. Obviously his right (shooting) hand is free and he's not being dragged. Since he shoots through the open window, his left hand is not impeded, otherwise he would have had to shoot Dubois through the rear side window.
It looks to me at 3:16 in the full video that his upper left arm is in contact with the door. He could just be crouching low or he could be off balance and supporting himself with his left arm on the door itself. The fact that he immediately falls when the car drives away seems to indicate the latter.
Next, show me where Dubois was grabbing him. Dubois has one hand on the steering wheel and the other on the gear shifter. He's not impeding nor holding Tensing.
It looks like the driver pushes the cop's hand away at 3:14 as the cop reaches for the keys. When the gun comes out the driver's right hand appears to be on the gear shift and the other hand is moving around a lot as if to ward off the gun.
Based on the video and measurements on Google Maps, it looks like after falling down, the officer gets up about 15-20 feet from where he initially approaches the car. He rolls up just past the no parking sign that was well in front of the stopped car. That's not a huge distance, but at minimum he was forced to keep pace with the moving vehicle to avoid injury. I don't think that is being "dragged", but I also don't think it is an outright lie to call it that. Moreover, it appears that at least one other cop (the one yelling "shots fired, shots fired!" and visible on the sidewalk at 3:22 in the full video) was close enough to see that at least from the opposite side of the car.
It will be interesting to see how a jury rules.
Full body cam footage:
https://www.youtube.com/watch?v=FicsKuLfpiw
