OK.The man who shot JD Tippit was Oswald.Much is made of the timing.Oswald couldn't get there on time etc. It's about a mile at the most from Oswald's rooming house to the crime scene. So if Oswald starts between 1.00 and 1.05 say and going at a brisk pace of 5mph he gets to the crime scene at between 1.12-1.17.
But who says he walked.He could've just as easily ran most of the way.In that case he would be moving at an average of 8MPH,In that case he could get to the crime scene between 1.08 - 1.13 or even earlier. It's just supposition to say he walked,It's also supposition to say he ran. If he did run then he is hardly going to tell Fritz that, as that would make it appear he was in flight.
So all this he didn't have time, is only supposition. So it was entirely possible for Oswald to have arrived within the time frame to kill JD. And there were numerous witnesses identified him as the cop killer.