Wilkes's book and the 'Crimes, hearts and coronets' article says movement was spotted. But does not say who spotted it.
Bews is on video saying two different things. Saying it was Jeremy and then saying it was a police officer.
The 'Crimes that shook Britain' video says it was Jeremy who spotted the movement.
It was a trick of the light, and no other movement was spotted that evening. However be good to have a definitive answer on who spotted it.
If it was a policeman who thought he saw something, then Jeremy had been convincing in persuading them about Sheila. If it was Jeremy who spotted it, then it was part of his plan to insinuate Sheila.