If you give your evidence against government officials to other government officials, good luck getting them bring a case that could hurt their career prospects by pissing off the wrong people.
To get that rolling under those circumstances, you need public pressure. Which means you need to distribute the source material far and wide, so that nobody can claim they don't believe it because they don't have access to it, and the whole internet can try to pick it apart use clues in the information to dig up more information etc.
None of that has anything to do with digital signatures or anything like that. It's a matter of seeing a video with a particular location and timetamp and then finding other documentation from other people for the same place and time, and looking up public records to verify that what you see in the video matches etc. That's how investigations work. You don't verify by having the original and some kind of signature, you verify with corroboration and the additional evidence that the original evidence leads you to.
Better to have the occasional tempest in a teapot than that people do nothing even when something needs doing.