It's really astonishing that after all this time, I never understood why PS Bews was saying what he was saying about the 'trick of light' at one of the first floor windows, when Jeremy's version of what they saw was so clear and precise, but now thanks to Nigel's prompting, I know exactly what has happened now - Bews was talking about a 'trick of light' at the wrong first floor window (Sheila Caffell's bedroom window, top right as viewed by himself), whereas Jeremy (and perhaps PC Myall) were looking and observing the movement of the figure at the first floor window (the parents bedroom)...
Nobody picked up on this at trial, or since...
Until now!