As I said, there's a big difference between them saying something, and them actually publishing internal documents about the case. I mean they can always lie about the documents themselves or modify them, but there's a very long history of intelligence agencies outright lying, even in front of Congress.

There's less of a history of them modifying or altering documents that they are forced to release.

Fwiw, I believe that Oswald did it, and that there's almost no evidence for any other shooter.