I have always wondered why Oswald would wait until the limo was moving away from him to shoot - I believe that has been covered, but I can't be sure until I research it.
Off the top of my head:
1: Kennedy was in the back of the limo, therefore a shot from behind gives a better target than a shot from the front. Whatever else you may say about Oswald, he wasn't firing indiscriminately: he intended to kill Kennedy and ONLY Kennedy.
2: With the limo moving mostly away it was hardly moving from Oswald's viewpoint, and so made an easier target to line up on and shoot (and he still missed once).
3: With the limo facing away from him so were all the secret service agents, meaning it would take longer for them to find him than if they had been roughly facing his location.
All points, as you may surmise, that I had not considered - especially of note is point 2: I had not considered that the limo would actually be moving slow enough that it would almost seem to stand still.
To my original point, I thought about it further and realized some things:
1. The windows do not quite line up with the windows on the TSBD
2. Even if they did, the evidence is clear that the shots came from the 6th floor window of the TSBD (eye witnesses reporting the gun, sounds, trajectories, etc.)
3. I have not proved it, thus this is only a theory, but I believe that if the shots came from the building across the street, the trajectories would have been to flat and the angles wrong. Further, I believe that the distance is too far and would have caused the bullet to drop too much - even with the 1100 FPS or so it travelled at.
Just sayin ...