If you look at the next 25 years, not only will every cop have a camera running 24/7, but also all vehicle's including the suspect's will be recording events from multiple angles.
Most homes will have cameras at the front door, and throughout the home in some form or another.
Many witnessneses are already recording things through their phones.
People may be wearing augmented reality style "google glasses" that can retroactively record important moments. Meaning they won't even intend to record the things that they do.
Right now its possible for the police to intimidate someone who pulls out a phone and starts recording, but soon there will be just too many devices, and it will be impossible to tell what is recording.
And drones... Traffic and delivery drones, can easily be rerouted during police incidents to provide overhead video feeds that help the officer, or help the court determine what happened at a later date.