Ultimately, you have to ask the question why, after over 50 years when the majority of the people involved in any alleged cover up are either dead or on their last legs, nobody involved has actually gone public and exposed a cover up?
I can't believe that some narked off policeman who thought he'd unfairly treated later on in his career didn't decide to get his own back by coming forward with evidence of any conspiracy. No fame hungry, attention seeking FBI official who fancied a nice pay-day courtesy of the press ever came forward with hard evidence of any cover up. No CIA agent ever wrote a complete confession on their deathbed outlining all that was done.
I genuinely can't believe in an age of reality TV where everyone wants their 5 minutes of fame and can get thousands by appearing on chat shows that not one single person involved would not have come forward.
Yeah, you've had the odd person come out claiming to be the 2nd shooter on the grassy knoll or whatever but as soon as this has happened everyone, regardless of your view on the assassination, immediately disregards this person as a fruitcake. Even those who for years have insisted a second shooter on the grassy knoll.
As soon as someone comes out that might validate their belief it's disregarded.
To me, that strongly suggests that nobody has come forward with any evidence because there wasn't any cover up!