The mentality that @OBESE is talking about can be seen when PD roleplays checking the gun barrel for temperature. I have only seen that being done in this way /do would the gun barrel be hot or warm? So you are already guilty when they arrive. I once said my barrel was luke warm and that i was shooting some beer cans on the mountain and came to the place a bit further away from where thr original scene happened and i still ended up in prison with no evidence at all except my gun barrel being luke warm and 99.99% sure no witneses saw a thing. So from my stand point it seems to me that most of PD doesnt even take any evidence except gun barrels temperature when it comes to shootouts. Other situation was similar but the thing was i havent fired a shot and i got killed for nothing when i tried to escape the shootout and get my self to saftey. Argument for that was that i am part of the same group of people that shot at the officer.
This is only my POV and i am not acusing all of the PD for this. I havent made an IA report as my character took it onto his chin and moved on. But if we dont know some basic protocols of how PD works criminals cant defend themselves and they (PD) can keep doing more or less what they want with suspects.