"Proof" of a fact is determined by the trier of fact - it is whatever evidence that is considered by the trier of fact to be sufficient to establish a fact. You obviously do not consider the abundant evidence of 3 shots to be sufficient to convince you that there were 3 shots. Others do, including all the members of the WC, HSCA. You appear to think that all that evidence is somehow wrong.
JBC did not say he was struck almost simultaneously with a second shot. He said he heard the first shot, realized it was a rifle shot and turned around to try to see JFK but could not as he had moved. As he turned back to turn to his left he said he felt being struck forcefully in the back by another shot. He says that as he lay back onto his wife he heard a third shot and felt the spray of brain matter over him. Even though he did not hear three shots, he observed three shots.
It is certainly possible that JBC's back wound was caused by a bullet that had not passed through JFK. In fact, one can make a reasonable case that in order for the bullet to have missed his right lung as it did, it had to have been travelling at a very small angle to the direction of the car - almost from directly behind. That means it struck him when the car was farther down Elm when the angle to the SN was very small.
Interesting, instead of just posting the proof for all to see this is what you decided was better information, which is basically nothing more than an unfounded fervent belief. The WC was not certain about the number of shots and stated the reasons in their conclusions.
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As usual you are quoting what a witness stated at a later time. Seems simple enough immediately after hearing the shot he just starts to make the turn he knows he is wounded.
JBC Hospital Interview 11/27
"I was sitting in the jump seat. I turned to my left to look in the back seat ? the president had slumped. He had said nothing. Almost simultaneously, as I turned, I was hit and I knew I had been hit badly."
In his statements JBC always thought the rifle shots were very close together
"were very, very brief span of time"
"Immediately after he heard the first shot"
"someone was shooting with an automatic rifle"
"rapidity of these two, of the first shot plus the blow that I took"
The only problem with father down the road, JBC was already wounded.