> Cops are sourced from the general population
They are notably not. Usually, immigrants are drastically under-represented compared to general population (at least in Germany, you have to hold German or European citizenship to join the police force).
> so incidence rates need to be compared to the general population
Oh hell no. Police officers act on behalf of the government and with powers that are both far greater than those of ordinary people and not immediately appealable. As a result of that, police officers in Germany are actually held to extremely high standards by law (§34 BeamtStG - https://www.gesetze-im-internet.de/beamtstg/__34.html) and receive at the very least two years of training.
I won't say our police are perfect (because they aren't, they still are a bunch of bullies), but they are orders of magnitude better than the trigger happy, barely educated (seriously, 360 hours of training?! - https://www.nola.com/news/crime_police/article_9dd5d48b-2152...) morons that make up the US police force.