This reminds me of the acoustical study that convinced the HSCA that there was a second shooter and a fourth shot. Of course, that study was never peer reviewed before the HSCA bought it hook, line, and sinker. Later that study was determined to be junk science. Why should we give Roselle and Scearce any more credibility? What are their credentials? Was their work peer reviewed? If not, it falls into the same junk science category as the Bolt, Beranek and Newman study that was presented to the HSCA.
Given the fact that you believe, correctly, that Oswald fired all three shots and killed JFK, why do you think Elsie Dorman, standing 35 feet away from Oswald's ear-splitting Carcano, jiggled her camera so violently at "Z-124" that she inadvertently turned it off, and why did you think she did it again at Z-222?
Do you think Roselle and Scearce are mistaken when they say
Kellerman began leaning over and looking behind/down to his right at Z-148,
Connally began a quick head turn left, followed by quickly looking back right at Z-149,
Jackie started an accelerated head turn to her left at Z-142,
JFK started taking a quick look to his left at Z-142, and
Nellie began a quick, sweeping head turn to her right at Z-144?
Bear in mind these aren't shoulder-hunching "flinches", but head turns, and are, therefore, voluntary responses to the sounds of the gunshot, not "startle reactions" that preceded them by about half-a-second second earlier.
You've said that the Zapruder film, unlike many eyewitnesses, has never "lied" to you.
If you try hard enough, you'll find the above-mentioned all-within-a-half-second-of-each-other movements in your beloved celluloid truth-teller.
Lacking any other documented loud stimuli at the time, how else can these nearly simultaneous head movements of all five limo passengers be explained as anything other than their conscious responses to the sound(s) of Oswald's first, missing-everything, shot?