He was in Dallas. He claims not to remember where he was that day.
How do you know that? Who did he make that claim to? A journalist?
So your theory is that Bush, then in private business, was part of a CIA organized plot to assassinate JFK when he came to Dallas. A successful plot at that, but that Bush, and his CIA associates, all failed to realize that Bush needed either a cover story to explain is presence in Dallas on that date, or to be somewhere else?
And then, knowing that his failure to have an airtight alibi risked having the whole CIA plot be unraveled, and Bush personally being in jeopardy of the electric chair, businessman Bush decided to run for Congress, causing scrutiny of his background. And Bush went on run for Senate, then accept appointments as UN Ambassador, and CIA Director, insuring that not only Democrats, but foreign governments, would research his past with a fine toothed comb, looking for dirt?
OK, then.