The following map shows the acoustically hypothesised position of McLain at Z255, between the vice presidential secret service car ( vpss) & the Cabell car.
It would obviously be of interest to see if Elsie Dorman shot any footage of Elm Street, between the times the vpss car & the cabell car passed directly opposite her window, because, according to the acoustics, Mclain ought to be passing across her field of view there, from left to right, somewhere between those two cars, at about 5 mph, in the left hand lane. It has been suggested that the vpss car trunk is visible in the Dorman film. The Cabell car certainly is. So let's look at the period just before the vpss is supposedly seen in the film :
Here is Elsie Dorman, panning during the 36 frames ( 2.25 seconds ) up to the 'vpss' trunk frame. The film is stabilised to keep the scenery there stationary. Thus the image moves around the scene as Dorman pans around , and may take a few moments to get used to.The steps in the backgound of the film are easy to find on the map above.
The red line is moving across the screen at the speed the Cabell car is moving, a few frames later, to give some idea of what McLain's speed should be.
McLain, according to the acoustics, manages to cross Dorman's field of view here at approximately that speed , somehow managing to avoid getting caught by Dorman's camera. I am not entirely sure this is actually impossible, but it looks very unlikely. Thus, there is no sign of McLain in the 2.5 secs before the supposed vpss car passes away to Dorman's right. He should be seen just behind the vpss car, at the end of the animation, where I have frozen the frame for one second.
Here is where he 'should' be (yellow area, below ) :
Here is that exact location in Dorman :
H B ( Buddy) McLain has vanished into thin air.
There is also no sign of him either in the following section, which takes us up to the time Cabell's car is passing.
see the following frames
Matching Zapruder to Dorman to Weigman
To sum up
1) Mclain does not precede the supposed vpss car across Dorman's field of view, we would see him in this frame -
2) Nor does he appear to cross it alongside the vpss car , or he would neccessarily appear in the yellow outlined area in the animation below, which covers that area ( he would appear as a rather obvious bulky object just left of the moving red line that gives an indication of the vehicle's speed . McLain would have to be above the blue line, to keep to the left of the vpss & Cabell cars ) . In addition, if he were side by side with the vpss car, of course, McLain would neccessarily appear in the Altgens Z 255 photo.
3) Mclain does not appear immediately after the vpss car -
4) Neither does he appear anywhere between the back of the vpss car and the Cabell car, when it makes it's appearance -
Click to see the frames between the one above & the Cabell car appearing
This appears to cover all possible locations from some distance in front of the vpss car right back to actually behind the Cabell car.
McLain , neccessarily present at this time & place in the acoustics scenario - crossing Dorman's field of view at the time the Altgens photo was taken at Z 255 - is conspicuous by his absence.