Witness testimony is already a very unreliable source of evidence. And again, evidence can be planted. Hell there was doubt about the chain of custody before AI could just make up audio and video. The validity of the chain of custody boils down to the cops and government in general being trusted enough to not falsify it when it suits them.
Sufficiently advanced AI can, and eventually will, be capable of creating deepfakes that cant reliably be proven to be false. Every test that can be done to authenticate that media can be used by the AI to select generated media that would pass scrutiny in principle.
I love the optimism and I hope you’re right but I don’t think you are. I think that deepfake AI should scare people a whole lot more than it does.