I don't accept the Zapruder film has been altered. Any argument I have ever seen in favour of this has been easily dismissed nonsense, my personal favourite being Costella's "Blunder of the Century".
That's for a different thread though.
I think this is too rich for another thread. I assume you are talking about Dr. John Costella, PhD:
Yes, it seems that the blunder of the century was Mr. Zapruder while rotating his camera to track the limousine failed to keep it perfectly upright as he panned across the Stemmons Freeway sign, making it appear that the Stemmons sign was rotating.
I wonder if Dr. Costella understands that it is the Earth that is rotating and not the Sun racing across the sky.
And, of course, in the middle of his explanation, he gets distracted by wondering where the hell the umbrella is. I don’t know. Why do polar bears disappear when it starts snowing? Maybe the black umbrella blends in with the black limousine in shadow.