Thank you for that reader. Somehow the window catch became ND/5 then RCW/8 Davidson explains how this could have happened. If Cook had made the exhibit RWC/8 then why did Davidson change it to ND/5 then back to RWC8 However, the COLP just took his word for granted and did not challenge it.
On the 1st of October Elliot and his team of forensics did a through search of the down stairs windows, so they might have been there at the same time. I do know that Cook was somewhere else on the afternoon of the 1st of October. Below is what was said in the 2002 appeal about Elliot...
On the 1 October 1985 Brian Elliott a forensic scientist examined the window catch and surrounding area of the downstairs bathroom/toilet sash window. He noticed that the brass catch had been scratched on the inner edge and that there was damage to the white paintwork on the adjacent faces of the top of the bottom sash and the bottom of the top sash. The white paint on the outside of the window including the outer face of the top of the bottom sash appeared clean and fresh.
So who is telling the truth here Cook or Elliot?

In notes written for the Essex Review (after trial) Barlow wrote:
"22/8/85 first opportunity to go to White House Farm. Examined all the windows. Most are sash type and could be opened from outside but could not be closed"