One of the few specials worth watching on the Discovery Channel and affiliates these days was "JFK: Beyond the Magic Bullet." They set up dummies with bones and ballistics gel, and the only thing that prevented their bullet from making the final wound was the fact that it hit 2 ribs instead of one. They also did a good job debunking stuff like the badge man and claims that Oswald couldn't have made the walk in time. Audio analysis is as close to conclusive as I think we can get with current technology to determining whether there was an extra shot, and at this point it looks like it was just 3 and an echo.
On a related note, I love this Onion story
