Trivia note: The "Shooter in the storm sewer" theory, with a guy armed with a Remington semiauto deer rifle with aperture sights, likely a .30-'06 in 1963 but really it could have been any caliber, was depicted in an episode of The X-Files. Limo comes driving down the parade route, a guy standing out on the street holding an open umbrella over himself (on a sunny day) where he can see the limo and the shooter in the storm sewer can see him. When the limo appears he pumps the umbrella up and down a couple of times. "Slow down, you're almost there", and "Here he comes, get ready to shoot".
Next thing you know the 4th grade teacher is walking into the 3rd grade teacher's class, visibly upset but keeping it together, and whispering into the 3rd grade teacher's ear... "Bzzz bzzzzz zzz bzzz THE PRESIDENT OF THE UNITED STATES bzzz bzzzzz bzzzz bzz bzzzzz"...
Where did you get the Remington deer rifle thing?
Some say it was a XP100 Remington .221 fireball pistol.
I never bought that, to slow to reload. I own one. At the time (and long after) it was the fastest pistol made. It is basically a 600 Remington action in a nylon stock with 10.5” barrel.