I have always liked the "Mortal Error" theory since I read the book in the early 90's, also known now after the latest show as the "Smoking Gun" theory
I am not sold on it entirely but I like the ballistics point of view that was put forth, I especially liked how he straightened out the Single bullet, path. I like the theory that the first shot was deflected by a pole or stoplight.. This gives a good reason why the easy close shot missed..
That is about where I stop with my beliefs in the possibilities of that theory, the rest makes some good sense, and it explains a ton of the cover up, but I am not sold yet :)
Also there was some conjecture that Oswald did have the rifle sighted for him, and was a very good shooter with the rifle... This came from a story from a Father and Son IIRC that saw him shooting at the range..
I do know for a fact that a rifle can be "Off" for most shooters and "On" for only one, my old hunting partner Joey shot opposite eye, he held Right yet shot with his Left eye, this meant that his scope was off for anyone else using his rifle... He could shoot it fine, yet I had to compensate over 5 inches at 100 yds to shoot it