Lem Johns, SSA for Kennedy was on the detail in Dallas. He married my great Aunt.
https://en.wikipedia.org/wiki/Lem_Johns
My dad talked to him a lot and maybe 10 years ago, Lem said "I am pretty sure there was a second gunman". But that isn't what his sworn statement said in 1963. Lem also told my dad that there was concern that maybe a secret service agent had fired his gun and struck Kennedy by accident.
The problem with the conspiracy theorists, to reach the second gunman conclusion, you have to make soooo many assumptions: (1) Oswald wasn't the shooter; (2) Oswald wasn't in the book repository --or at least on the 6th floor; (3) Oswald couldn't have fired 3 bullets because he couldn't have made the shot, etc, etc.
Oswald was insane and complete unreliable--even his wife said so (although she has since meandered all over the board on this issue). The KGB didn't want him (Note--the soviets were scared to death that the United States would launch a nuclear strike following the Kennedy's assassination that they launched a full scale investigation into the event. These files were released following the fall of the Soviet Union. You can find them online someplace. Oswald did run from the police and he killed officer JD Tippet. A lot of noise there if you didn't do the shooting or weren't in the book repository.
The Warren Commission was a bit of a joke. Anything will Allen Dulles involved we should be highly skeptical of. Not just because Dulles and Kennedy hated each other (they did), but because Dulles was the proverbial dirtiest player in the game domestically and overseas. The House Select Committee on the assassination dug down pretty good.
The one point that has always bothered me was the involvement of Jack Ruby and his murder of Oswald. It literally makes no sense. Ruby was not some altruistic guy at all yet he claimed he was doing it so Jackie O didn't have to go through more pain. I don't buy that at all. Maybe there is something there.
Regardless, there will be nothing of real significance that will be released, the players are all dead and with them any secrets that may have existed.