It seems the police need to improve their accuracy. I bet he fell instantly even with the misplaced bullets. In over 38 yrs of crime scene reconstruction, I personally have never seen such penetration by a handgun bullet but I have heard a lot of embelishment by offenders. I question why the window would be penetrated first, maybe last but unless they are shooting into the window from outside and that is unlikely.
In this case, I would question how he knows it was the same bullet doing all the damage. Breaking it down, most BB guns will penetrate a double pane window. A pellet gun can penetrate such a window and a vase. A .22 caliber will do the same and into a human body. Past that, there has been so much momentum lost that little will begin penetrating walls. Even using 1/4inch wallboard, that would be a half inch of wallboard, not counting the other items. With penetration comes parasite drag and resulting co-efficient friction. A rifle bullet may do it but handguns would if they are hot loads.
We spend hours studying what happens at a shooting and why. Often the area is sealed for weeks in the event we need to re-examine something. It is all needed so fault can be determined and wrongful actions decided. The path of each bullet is traced with some expensive equipment. In the event of shell casings on the floor, ground or etc, their position also tells us pretty much where the firearm was when fired, the way it was being held and the location of the shooter. My degrees are in engineering and law as well as in business. All my education, training, experience, equipment and court testimony is examined each time I testify unless there is stipulation approving my credentials. Many people do not understand all that goes on in the background after a LEO or criminal shooting.