Make it a felony to conceal or destroy body cam footage.
Also, make it so that if a cop is accused of violating rights or involved in foul play, and their body cam "suddenly malfunctioned or were turned off or was left in the car" , a default judgement is given against the officer in question.
Make it as ubiquitous to cops as a parachute is for someone who goes skydiving. This must be enforced as harshly as possible. Cops aren't operating on their own dime.
If I'm a cop and the choice is leave my camera on or lose my job, my union membership, my retirement, my pension, and also face serious jail time, I'm leaving my camera on every time.
The watchers MUST watch the watchmen, and the watchmen must have no expectations of privacy while on duty or being paid by the public.