Earlier quoted context omitted.
We just need to establish a legal precept that if the body cam footage isn't there to corroborate the cops' story, we assume the worst and they get held accountable for anything a plaintiff is able to plausibly allege. Under that scenario, most cops would become the biggest advocates for e.g., redundancies, backups and transparency.
This seems to abolish the right to be "innocent until proven guilty". It's always possible to allege a crime that no one can prove didn't happen ( https://en.wikipedia.org/wiki/Russell%27s_teapot ), so without a presumption of innocence, the system essentially puts the accused at the mercy of the accuser.
When cops' word weighs more than yours in a court of law, this requires an equivalent check against that power by only making it weigh that much when there is corroborating evidence (i.e., video proof).