I think the US made it very clear what will happen to you if you provide proof. Better prepare for a Snowden life in the best case. If you are less lucky you might end up Assange.
We're living in age where military base layouts are leaked by fitness trackers. Top secret battle maps leak onto Discord video game channels. Not even as an act of spying, just by accident or carelessness. I just cannot accept that any truly massive secrets could be kept sealed for long. It's the same reason the Area 51 conspiracies are bunk.
How do you expect evidence to be presented when even acknowledging existence of such possibility is highly illegal? Garry Webb suicided with two gunshot wounds to the head.
> "If we had met five years ago, you wouldn't have found a more staunch defender of the newspaper industry than me ... And then I wrote some stories that made me realize how sadly misplaced my bliss had been. The reason I'd enjoyed such smooth sailing for so long hadn't been, as I'd assumed, because I was careful and diligent and good at my job ... The truth was that, in all those years, I hadn't written anything important enough to suppress."
[..]
> Webb's ex-wife, Susan Bell, told reporters that she believed Webb had died by suicide. "The way he was acting it would be hard for me to believe it was anything but suicide," she said. According to Bell, Webb had been unhappy for some time over his inability to get a job at another major newspaper. He had sold his house the week before his death because he was unable to afford the mortgage.
So he was killed indirectly; not a distinction I personally care about. Unless you are investigating state crimes yourself, I wouldn't throw popcorn from the cheap seats.
It’s difficult to provide proof when the act of doing so is either illegal, or gets you targeted by a major nation state. We may never get proof. We may only get proof decades after the fact when it becomes irrelevant.
In cases like this we have to weigh the likelihood and risk regardless, and proactively protect ourselves.