First off, congrats to officer Jessop for his quick thinking and fast response to the situation. He is without blame or guilt in the incident as the video clearly shows.
Second, thank your favorite diety for drunken, incompetent, and stupid people like Davis. Had he not been drunk and and stupid, he might have actually succeeded in firing that hand cannon.
Third, Davis was a convicted felon and was still able to obtain a firearm. this, along with the thousands of other felons who have obtained firearms is clear evidence that all the forms, bureaucratic red-tape and delays required by numerous "gun laws" aren't worth spit.
Re: Coroner's inquest - The investigating agency apparently did a thorough job. Not only do they need to show that lethal force was justified, but they also need to show that (a)the contact was legally justified, (b)the officer followed proper procedure during the stop and (c) anything non-obvious that the officer knew about the subject or situation. Other facts - like the officer's use of approved ammo types, his firearms qualification and perhaps any prior complaints on his use of force may be relevant (in some cases). That's what takes 5 hours to review.
Jessop's Glock 22 is a .40 S&W pistol. Its performance against automotive sheet metal is generally good. It is likely that the fatal round went through the large window opening after the glass shattered. Unencumbered by metal, it could easly penetrate two seatbacks to strike Davis.
Had Davis been less drunk and more aggressive in his intent to kill Jessop, he might have succeeded. The .41 Magnum's penetration against automotive bodies is excellent (quite often penetrating both doors easily). Jessop's car doors would become concealment, not cover.
S&W .41 Magnums - Model 57's and Model 58's (fixed sights)
Re: Tactics -- Besides Kmar's comments, I'll add that we were taught to make the initial approach to the B-pillar and assess the situation. That includes a visual look at the occupants, their hands and the areas around their thighs. Plus the attitude of the driver and occupants. Once you're satisfied with the situation you move a step forward to see the front seat area better.
However, if you get "bad vibes" or suspect that the driver is going to get hostile you tell him to wait and back off carefully to radio for back-up. Unfortunately, incidents often unfold - like this one did - with little warning that the driver is going to go Bozo on you.
For the most part, an officer's "escape" route from the kill-zone is to move to the vehicle's rear... behind the line of the B-Pillar (making it difficult for the driver to bring his weapon to bear and/or aim) and staying away from the "crush-zone" between the vehicles.
Officer Safety Tip: Before leaving the car, hang the radio mic out the window. One of our local officers in the early 80's was wounded on a car stop. But a 9mm round hit his HT radio too. He dragged himself to his car and managed to get the door open, but couldn't reach the microphone. Fortunately a citizen came to his aid and he survived.
Note that Jessop thought he fired 7-8 rounds when he nearly emptied the magazine. This is a typical stress-related problem. Your focus is on stopping the threat, surviving and getting help on the way. These are far more important than counting your own shots.
By the way... was anyone else astounded by the sound of that .41 Mag going off? I'm surprised Jessop isn't deaf in one ear now.