Lending the Key to the Locked Room

Ryuhei, a would-be film director, has just been dumped by his girl friend and his drunken threats to kill her have made him the prime suspect, as she has just been murdered. His alibi is that he was watching a film in his friend's home movie theatre at the time. Unfortunately, his friend has also been stabbed to death in his bathroom, with the door to the apartment locked with a door chain. Worse still, Ryuhei was the only other person in the apartment at the time, and passed out until the following morning after he discovered his friend's body. Fearing that the police will not believe him, because the door chain can only be locked from the inside, he panics and runs away. Not a good idea.