"After Oswald was shot, an unknown policeman administered CPR, which is the worst thing you can do for an abdominal gunshot if you want the person to survive it."
Maybe that brought it down to 50-50, who knows what Ruby was thinking and if he knew that fact back in 1963 maybe he would have gone for a head shot, we don't know.
Something for your viewing pleasure, it's essentially a shortened version of "JFK - The Smoking Gun" and it's free on youtube