Not really, but if the human part was only referring to 'living humans', thenit is possible for another of the cousins to have entered the room and then died in there. It still becomes a closed room, just wanted to ask if that was a possible action or not.
Not completely clear what 'time of murder' refers to,so here I go:
Bill stabs the owner, gets out through the door, and in his dying moment, the owner locks the door and sets the chain
Bill stabs the owner, gets out though the window, and in his dying moments, the owner closes the window
The owner has a son (or daughter, or another close relative) that through heritage becomes the new owner upon the old owner's death. When Bill has killed the old owner he drags out his corpse, and afterwards the new owner gets into the master bedroom and locks himself in.
Or, with the same assumptionas above, the new owner walks into the master bedroom and find the corpse, and immediately locks himself in
Now, some (all?) maybe breaks a red truth or two depending on your definition, but I have to try!