There are reputable historical accounts that include evidence that was taken away by authorities.
What missing evidence would you like to see?
Perhaps a FOIA request?
Sad when such evidence exists, but the US White House says "we know nothing".
Let's start it off with astronaut Gordon Cooper.
He claims (and I have no reason to doubt) that he and a group of photographers were shooting video of training exercises at Edwards AFB in California when a saucer LANDED NEAR THEM. Video of the landing was taken, and he later confirmed it was GOOD video. The film was sent to Washington DC.
WHERE IS THIS FILM TODAY??? Missing Evidence.