Anyone who has seen somebody shot in the head with a rifle caliber bullet will probably agree that the front right quarter of JFK's head bursting is an obvious exit wound. Rifle rounds, unless they are tumbling, create a nice small hole when entering, almost like it was done with a drill. I've seen it many, many times, and the entry is nearly always the same. The exit on the other hand, varies depending on the ammunition used. If, for example, JFK was indeed struck by a negligent discharge from a 5.56 rifle round, as the latest TV show claims, it would indeed look pretty similar to the video.
I'm sure a few of the US Army vets here who were in Afghanistan can comment as well on head shots, and what they look like. I'm fairly certain they'll agree having the same frame of reference.
So, unless the round that hit JFK was tumbling, or an explode on impact type of round - pretty unlikely in the early 1960's, yet possible I suppose, there is little change that he was struck in the front right of the head, and a very good chance that he was struck from ground level, not the elevated position in the book depository, as the exit wound's burst pattern and position also strongly supports this.
You can't shoot a watermelon with your rifle and expect the same results as a human skull - a melon will usually just come apart from a rifle round, but the human head is much different - as I said, small entry hole like a drill in, somewhat unpredictable mess going out.
If in fact a Secret Service agent did have an AD/ND, it would explain a lot about Oswald. His shooting feat isn't nearly as improbably since he only would have got ONE hit, not two in the time frame that's been used throughout history to try and replicate his shooting with that crappy Carcano rifle. In fact, the first round he fired was likely a miss then, and his second struck JFK in the throat/upper chest. Or whoever was shooting from an elevated position at least, Oswald or not. But it does certainly make it more likely he could have possibly been the shooter, and alone, if the head shot on JFK was an accident from an agent who made the mistake of finger on the trigger, and was startled by shot number 2 and squeezed.