You're conflating police murder with police homicide. The difference is that some (hopefully almost all) of the time the police kill someone, they are justified

You're conflating police murder with police homicide. The difference is that some (hopefully almost all) of the time the police kill someone, they are justified in doing so. 40 is what we should expect for murders - i.e completely unjustifiable killings. This is also blurred a bit further because we can imagine a class of killing that's "kind of justified" that we'd expect the police to sometimes engage in. Something like killing through negligence or incompetence. A certain fraction of people are likely negligent or incompetent. If you're an incompetent plumber, pipes may burst. If you're an incompetent, lazy, whatever police officer you may cause someone to die. We should also expect some level of this too.