John Kennedy was known for riding around in convertible limousines. He made himself a sitting duck. The parade route in Dallas was published on the front page of the Dallas Morning News a week before Kennedy arrived. There was a kook in Dallas named Lee Harvey Oswald who owned a rifle. The whole world including Oswald knew Kennedy rode around in convertibles. He seen in the Morning News that the parade route would pass right by the building he worked in. He set up a sniper's nest. When Kennedy rode by Oswald shot him.
That's the hard evidence. Then there is the conspiracy nonsense.