No it wouldn't. Not if it's a standard sliding lock. The hasp is usually notched as in this picture:
The notches are probably on these kinds of locks because they'd be easier to jimmy open (by someone trying to get in from outside) if the sliding part of the lock moved smoothly back and forth.
True, it isn't usual. But FWIW, two doors in two different places I've lived in (both in older houses) had/have this kind of lock, also placed vertically, in a similar spot -- vertically above the door, and left of center. One is on the door to my balcony currently. In the other house where I lived, the lock was painted white like the moulding around the door (as the lock in the picture appears to be). It may not have been used in a long time, but still, it was installed at some point and it still worked. It's possible the Ramseys didn't even install that lock and it was there when they moved in, as both of them were in my case.
I am RDI, leaning towards PDI. But I believe we should be accurate about every detail.
All that said, two things are chilling to me -- that the golf clubs were so close to the WC (weren't the golf clubs one of the items removed from the house very quickly?), and that the
door was latched. I didn't know these details before.
Even supposing he noticed the lock at all, a killer would not latch it to buy time; it was the Ramseys' house and they would know about the lock. It would buy no time whatsoever. And if the killer entered/exited through that window he obviously couldn't have locked it behind himself.
I believe someone locked it from sheer habit, unconsciously, upon leaving the room. We all do things like that, especially if preoccupied and/or in a hurry. We run on autopilot and do things we don't have a conscious memory of doing -- turning off a burner, etc.
Also, can anyone tell me if there was a table in the WC? If not, I don't buy that PR wrapped presents down there. She'd have to sit on the floor. Look at the rest of the house -- imagine how dirty the floor probably was. It was a big house. She couldn't take the presents into
any other room and lock the door?
Does anyone know if the WC door locked from the inside? If not, again it makes no sense. Curious kids could follow her down there and just walk in. "Whatcha doing, Mom?"
I'm curious what the IDIs think about the latched door, and what explanation they think there could be for it.