If you're interested in other things IPRA 'investigates', some people have FOIA'ed Chicago police misconduct complaints and created visualizations based on the data[1].

[1] http://invisible.institute/police-data/

Devils advocate but wouldn't they investigate every shooting incident, so you'd expect the vast majority to be clean.

I know every discharged weapon in the UK is followed by immediate officer suspension and investigation, and I suspect very few are actually ruled as bad and rightly so.