You appear to be permanently gobsmacked:
1) The nonsensical part is setting up the 'patsy' behind the limo and then claiming the shots came from the front, Kneelin' JudgeJohnny.
2) For the clever, cut-to-the-quick insight, see above.
It's like these conspirators were playing conspiracy poker.
Powerful conspirator "A": "Let's shoot JFK in broad daylight, in the middle of the street, with hundreds of people watching and with many having cameras."
Powerful conspirator "B": "I see that and raise. Let's shoot him from the front and then change everything to make it look like it was from behind."
Powerful conspirator "C": "I see that and raise again. Let's frame a guy and then force all of the eyewitnesses there to go along with us. Then make them remain silent for the rest of their lives."
Powerful conspirator "D": "I raise and call. Let's then have multiple investigations of the shooting and require all of the people to cover all of this up. Forever."
People, seemingly intelligent human beings, believe this. We've seen people in the past believe in witches and all sorts of strange things like demons and ghosts. We think to ourselves, "Well, we're smarter now, science proves there aren't witches. This type of superstitious belief is no longer believed."
Yes it is.