I'm not looking at solving the case from this visit but to look at certain issues that are not explained. Whooshing curtains, slamming doors, locking the apartment, main bedroom window security.
Rob,
I don't quite see what you'd be able to do.
- The place has been sold. Whether or not the new owners would welcome yet another armchair detective poking around the flat remains to be seen.
- You wouldn't be able to check out anyone getting in or out of the kids' bedroom:

- You won't be able to check the lighting as the street lights were replaced shortly after she disappeared, there's a large projector on the building that wasn't there before and the big tree that could have given cover has been chopped down.
- If the new owners put up a wrought-iron thing over the window, they may well have also changed the lock to the main door while they were at it.
- You can test a slamming door and whooshing curtains without leaving home or not going very far to a friend's house. I very much doubt that the PJ hasn't already checked that out.