question about the blonde (spoilers)
during the big reveal, the policeman starts talking about the shoebox they found in the young man's flat, containing items that the blonde had reported stolen a few days earlier.
Why would she have reported the burglary to the police? Breaking in to her place was part of the plan to get the young man interested, the plan that she was going along with.
Reporting it to the police would only have made sense if she was actually going along with the other plan - to frame Bill for her own murder!