Our system doesn't assume criminal guilt under any circumstances, by design, and that's a good thing. Everybody accused of a crime has the right to a trial, even cops.

Let me expand on what I wrote: From a professional perspective, you should be assumed guilty, and probably loose your job, if you are accused of something and your body cam was not on. Because even if the accuser is lying, why was your camera off?

From a legal perspective, I think a cop without a body cam should be given the exact same rights as a private citizen, including around the use of force. The right to use force comes with responsibilities, like having a body camera.

And when standing in court as a private citizen, a body cam which just happened to get turned off at the exact time of the incident should be viewed with extreme suspicion. Not proof in itself, but a very serious black mark.

That's not entirely true. There are a category of legal defenses called "affirmative defenses" [1] where you are presumed guilty and have to prove beyond a reasonable doubt something that makes your typically unlawful conduct lawful. Self-defense, insanity and fair use are common affirmative defenses.

I would expect affirmative defenses to be fairly common in trials involving police; there's typically not a lot of argument around whether an officer assaulted/killed someone, just over whether the use of force was authorized.

That being said, I would be more in favor of changing jury instructions to indicate that the lack of body cam footage can be seen as an incriminating factor. Not that it 100% means that they are guilty, but that it can be considered suspicious circumstantial evidence. Much in the same way that you cannot be compelled to self-incriminate, but that juries are allowed to interpret invoking the 5th amendment as incriminating.

[1] https://en.wikipedia.org/wiki/Affirmative_defense