So if I understood it correctly, there exist no keys for the rooms in the guesthouse (except the entrance door, for which we have a key).
As can be seen with these red truths:
- No key exists that can lock or unlock a door to any of the three guestrooms.
- No master key exists for the guesthouse. Any key to the guesthouse is for the front door only.
Together with this:
Without the use of a key, no method exists through which it is possible to unlock a locked guestroom door from outside the room!
*It's also not possible to lock a door from the outside without a key.
we can assume that it's impossible to unlock the door except you enter the rooms through the window.
To repeat my thread of thoughts: You need a key to unlock the guestroom door from outside + No key exists that can (un)lock any of the three guestrooms --> It's not possible to (un)lock it from the outside, even by using tricks.
So, here's my take on the crime:
Theory 1:
Though not confirmed, the witch part of the story suggests that the murderer knows my cousins and warned them. Because of this (or some other reason) the murderer prepared the house so that the doors can be easily removed and put back into place without doing much rumor. This way he entered the guest house and the three rooms and rearrenged the scene after each murder.
Theory 2: Basically the same except that this time the windows can be taken out of the wall and put back into place.In both theories, the doors or windows are not unlocked from the outside. I admit though that the one with the doors is unlikely because of the sliding bolt.
@TheWitch: Can we assume that everything except the part written with different style, namely the witch part, is true? Because I have a feeling that otherwise the amount of theories we can come up with is immense.
Assuming my theories don't work there are other things that bother me:
Because of red truths I don't want to look up the following things are given (assuming that the answer to the above question is yes).
Anyway, I don't remember all the red truths but reading them through I didn't find one that contradicts the following theory:
The murderer enters through the windows left open by the cousins and kills them. He then seals the windows and unlocks the door. He uses a string or a cord and attaches it to the sliding bolt, exits the room and closes the door from the outside.
Since (s)he can't leave the guesthouse now, (s)he hides (maybe under the table) and waits until I rush out in the morning and leaves then the house. According to the red truths I don't break or remove the seal and it's nowhere stated that I can't perfectly seal it from the outside. You only forbid to perfectly seal windows from the outside which in my theory is not done. Or is the cord considered indirect? In that case my theory does not hold.