Close enough, I'll go ahead and concede defeat here.
The culprit went inside the room, set the chain, and also made a fire in the fireplace before going to sleep.
At some point during the night, Kinjo dressed up as Santa Claus and went down the chimney, into the room.
However, once he arrived at the bottom he came into contact with the flames, and was scorched to death.
not even gonna try one last theory, I honestly have no clue