Yeah, I'm not a conspiracy theorist but there are definitely big things held back from the public.

Example: https://en.m.wikipedia.org/wiki/Project_MKUltra

> The operation was officially sanctioned in 1953, was reduced in scope in 1964, further curtailed in 1967, and officially halted in 1973.

and

> Project MKUltra was first brought to public attention in 1975 by the Church Committee of the United States Congress...

22 years they kept that from the public. Seems like they did a pretty good job keeping that secret.