I dont know about others but I find this locked door to be a bit of a red herring. I know how often I return home from a day at the office with my briefcase and various work documents thus my hands are full yet I am still able to unlock my deadbolt.
The other part of this is that there is nothing in MK's room to suggest that AK or RS were in that room so I would think the person whom has been identified to be in that room probably had the most to gain from locking it
To my knowledge FR's room was not locked but the door was closed when both AK and RS returned. It was then opened by them.
Considering that we now know that it was a very windy night I know how often my doors slam shut when I leave my windows open
I think you might be explaining something different than what I'm talking about. I guess I didn't explain myself properly.
I expect that RF's door would be unlocked and either open or closed on the day of the murder.
However, the night OF the murder, I think her door was locked before the break-in.
I think she locked it because she was going away for the holiday. This is why I think she locked it:
1. RF, or the court in her testimony, claims that she went through the effort to attempt to secure her window because she was going away. if she was making an attempt to secure her room, and had a key to lock the door, it would serve to reason that she'd also lock the door before going away.
2. The reason she thought she had to secure the window. Apparently, she thought she had to lock it because what? Because she must have thought someone was capable of getting in that way. So why wouldn't she think all these "strange people" AK allegedly brought home wouldn't go in her room unless she locked her door?
3. Additionally, she knew that the front door had a potential to come open if not secured properly. So why not be more worried about locking your room door than a window that NO ONE IN THE WORLD thinks RG could have scaled?
I contend that on the night of the murder, RF's door was locked. RG broke in the window, came in her room, and to get to the rest of the house, he simply unlocked RF's door.
IF RF had indeed locked her door before going away and AK had no key to it, AK could not go in there to stage a break-in.
I theorize that Laura's door might have also been locked, which is why RG didn't go in there. He'd have to make effort to break it down. That might have been something he WOULD have done later, had he not been interrupted. AK's door could or could not have been locked, I don't know, since she hadn't gone away and had just been there earlier in the day.
I agree with everything else you've said.