Listen to Jack Ruby's lawyer, Tom Howard.
"He told me that the first thing he remembered of the shooting itself was when he was in the Homicide Office after the shooting, and he says they were shouting at him, 'You shot Oswald! Why did you shoot Oswald?' And that is really the first recollection he has of it. I would think that we would plead at least temporary insanity."
You can listen to Tom Howard say that here at 54:10.
The reason Jack Ruby had no memory of shooting Oswald is because he didn't shoot him. He reached the garage well before the spectacle. There, they jumped him, dragged him off, took him up to the 5th floor, and that is where he was during the televised spectacle. Then, they gingerly brought him down to mingle him in the post-shooting scene in the jail office, but they forgot about his jacket.
The bit about Jackie Kennedy is ridiculous. She would not have had to testify at Oswald's trial. Who would have called her? The prosecution? What for? The defense? What for? What could she possibly say in support of Oswald's guilt or innocence?
Jack Ruby was innocent. He correctly remembered Lt. Rio "Sam" Pierce, so why wouldn't he remember shooting Oswald if he had? He did not shoot him. You can't remember something you didn't do. Jack Ruby was framed and innocent, and he is the most manipulated and abused defendant in the history of jurisprudence. The Dallas Police killed Oswald and framed Ruby, knowing that he would believe whatever they told him.