Some observations:
1) Not apparent from the endless documentary films about the Nov. '63 events is that the plaza is SMALL. I stood on the wall where Zapruder stood. The distance from there to the bush/fence on the grassy knoll (where "badge man" can be seen in the photos) is approximately 20-25 feet. From years of seeing documentaries on TV, I thought Zapruder was 30-40 yards from the grassy knoll. I was astonished at just how close the fence on the knoll is to where Zapruder was standing. Now, if I'm Zapruder and I'm filming, when suddenly a high-powered rifle goes off 25 feet to my immediate right, I would surely be startled and bobble the camera. I'd also look to my right, not calmly keep filming a motorcade.
2) I also stood behind the current stockade fence on the grassy knoll. Assuming that back in '63, it was the default 5' or 6' height for a fence of that type, you would have to be 6"5 or so to shoot over it. I'm 6'2" and could see over it, but would not be able to depress a rifle barrel enough to shoot downhill to the road below. I guess the second shooter had a milk crate to stand on??
3) If you stand at the fence and look to your rear, the railroad yard control tower is in plain view about 50 yards away across an open lot. Nowhere to hide.
4)Elm Street has a pretty steep downhill pitch as it runs down to where Kennedy was shot. From the book depository window, a target travelling away AND downhill from the shooter is easier to hit than one travelling away on a flat surface, as the distal movement of the target is more gradual. Try it yourself by sticking your thumb up infront of your face and moving it straight away by extending your arm. Next do the same thing while moving your thumb away from your face, this time at a downward angle. The distance from your eye to your thumb increases at a slower rate (making for an easier shot) when your thumb is moved away with a downward angle 5) I also stood in the window in the Sixth Floor Museum that is about 8 feet from Oswald's perch (Oswald's window is behind a plexiglas barrier). Looking out at the cars going by on Elm St, it's really a pretty easy shot. Having a vertical height advantage on the target and having the target moving downhill to boot, makes it not too hard to do.
In conclusion, I think Oswald did it. The bullet ballistics consipricies seem to be all based on the asumption that bullets travel in a striaght line. They do, until they hit something. Once inside a body, they can caroom about and come out at weird angles and with a trajectory entirely different than their original one. Oswald was having a really accurate day of shooting that day, just like some golfers have exceptionally good games on occasion.