The cleaner in the apartment on WED. If she cleaned the window (as Amaral claimed) she would have locked it if not secure.
"On the window, there were no signs of a break-in or of gloves. It had been cleaned the day before, May 2nd, by an Ocean Club employee, and the only fingerprints found were Kate's." Chapter 18 Truth of the Lie
As a seasoned traveller, staying at 4*+ hotels generally, I can tell you that in my experience the only time that a cleaner at a hotel / apartment complex in Europe would clean the windows would be at change over day. Unless the window was in a complete mess
As the window was not used and the shutters were down, it seems unlikely to me that anyone would go near that window to mark it in any way. It also seems quite likely that the curtains would not have been pulled back at all, cos the window would have been a pretty depressing sight with shutters down.
I am sorry, but I find it difficult to believe that
1) there was any need to clean that window
2) the cleaners would have cleaned them except on change over.
So what I am saying is that imo, one of two things happened here:
1) Amaral embroidered 'it' to try and make a case against the Mccanns
or
2) the cleaner "bulled up" the work that she had done