The CIA had Kennedy killed because they knew that Kennedy was trying to disband the CIA.
The CIA came to Oswald with an offer to kill Kennedy, Oswald declined. An as of yet unknown assailant shot and killed President Kennedy.
The CIA put the rap on Oswald and he was arrested and booked. When Oswald threatened to rat, the CIA recruited long time associate Jack Ruby to quiet the Rat.
Ruby was booked and tried to kill himself several times. He expressed that he was the only one who knew the real truth. He took the secret to his grave.
As more time goes by, more evidence shall be released. I see a future where we are finally told the truth, and the true criminal entity shall be brought to justice.
The story runs much deeper than the opinion expressed here by me. Government expects to withhold info as long as possible; hoping the public will lose interest.
I have some disconcerting news for those holding out of important info: One day will come and it will not be pleasing to you.