Are you suggesting that Oswald would have had to wait for the first shot in order to realize that the gig jig would be up?That's what it sounds like it: ["Once the first shot rang out the shooter would logically assume the gig to be up"]
"Trying to part Kennedy's hair prematurely (making an attempt with the limo still on Houston) would be tantamount to saying 'Here I am. Come and get me'". At that point would the jig me up? When ever the first shot rang out. Agree?
After the second shot we can see multiple agents looking back to determine the precise direction of the assassin but still not one of the agents appears to be looking up. JohnM
All very well in hindsight. The discussion was what a potential assassin might logically believe before the first shot was fired.