I agree that some "old school" people might not easily adapt to change and it does happen in all professions. (most of the people who resist change end up being fired imo). But as a cop, his ongoing training demanded compliance to LE's warnings on the danger of putting a person in the prone position. That's not a lesson that any cop should ignore, regardless of their experience and years on the force.
I agree with you in part (looking for an explanation for a career cop who wont adopt change) but it is obvious that he has acted in a similar way throughout his career, regardless of regular training, and despite many complaints. He should have been fired years ago, and the fact that he wasn't, gave him more power to be capable of being charged for murder. jmo