It's simple. You encrypt the data. Only the DA has the key. This also prevents the police from being able to use their own footage when trying to make a statement, a benefit the public doesn't have.
If the DA determines that a crime was likely committed, then they can decrypt the footage and review, otherwise it stays stored for a short period of time, then destroyed.
This scheme assumes DAs are trustworthy, but there are a plethora of cases where DAs have protected bad cops. If only the DA can decrypt the video, that severely limits the opportunities of would-be whistle-blowers.
If the DA determines that a crime was likely committed, then they can decrypt the footage and review, otherwise it stays stored for a short period of time, then destroyed.