Oswald in the doorway: the blog of the Oswald Innocence Campaign, by Ralph Cinque

 From his hospital bed a few days after the assassination, Connally said that they heard the first shot right after they made the turn. 

Of course, that didn't mesh with the official story, but the official story wasn't out yet. But, what shot was that? If they had wanted to put a bullet in Kennedy's head at the top of the Plaza, they surely could have done it. But, they did NOT want to kill him there, not with all those people around and all those eyes fixed on him. They wanted to wait until he got down to the Grassy Knoll area where there were few people and half of them were operatives. 

So, the shot that Conally was referring to was the shot that I talk about; the preparatory shot; the one whose purpose was to incapacitate Kennedy, physically and mentally, so that once the real shooting began, he would not be able to take evasive action. And you can plainly see in the Zapruder film that he was intoxicated, and he was seized up in his muscles. Now, that has to be accounted for, and the only thing that can account for it is that he was poisoned. This was before the fatal head shot, and he did not suffer any trauma to his central nervous system, to that point. So, it had to be due to poisoning, and that was the purpose of the first shot, to poison him. It was an icedart containing a nerve agent, most likely paralytic shellfish toxin.  And, it may have contained more than that.