While I agree with what you say for the most part, it's not a question of "what rules can we add on top of the existing structure?". Which is why simply adding bodycams has been so ineffective. We're only really going to be safe from cops by essentially nuking the entire system and starting over.

The core issue is that cops are far less vulnerable to prosecution or even non-legal accountability than almost any other citizens. Largely this is due to police unions. In addition to the structural inertia, there's cultural inertia - cops don't want to hold each other accountable either.

This is why people talk about reforming police from the ground up. It's actually easier than "fixing" the current system, which actively fights against accountability.