Where can you go to have lunch with Jesus?
Governments gather the physical evidence and hide it away. It scares them; and, they want to harvest it for weapons before "the enemy" does. Where can YOU go to touch an atomic bomb? Can you put your hands of an F-35? You aren't in the "need to know" you have no knowledge or skills that further the understanding of those things. You aren't "read in". You wouldn't be trusted.
If you worked for the government and came into possession of something that would give you a significant edge over our enemies; and, knowledge of that material might give a significant edge for the enemy, would you go public with it, or hide it? If that same material were known to make people like you go catatonic, would you go public with it? You might benefit from pretending for a moment that this is all real, and then try to figure out what you would do. Factor in just coming out of a world war with a substantial and dangerous enemy that has an extensive sky network in your country. What would you do? Attempt to be realistic.
“Where can you go to have lunch with Jesus?”
This is sidestepping the question.
“Governments gather the physical evidence and hide it away.”
This is handwaving.
You said there is tangible evidence, but you can’t produce it. You haven’t seen it, or touched it yourself. So that’s not tangible evidence. At best, it’s hearsay - “Some guy told me that he saw the murder weapon, your honor, but it’s gone and we can’t produce it.”