Doesn't matter if your device is designed in such a way that it can stream content in a clandestine way, so that it's hard to verify whether it is or not, while sleeping. Of course you can always bypass things like this by starting the whole interaction by grabbing the phone and placing it somewhere else, but that would imply intention which may be even more damaging in a future court case if it could be proven from the phone that it was removed (which you can if it was already recording and streaming) -- and I'd like to think that most people can agree across party lines that police shootings do happen in the "heat of the moment" rather than as planned out homicides.
It also sure wouldn't hurt with mandatory police cameras, it would help police as well as long as they behave, and auditing an official like that shouldn't be controversial.