The kid has nothing to do with the landlord. The landlord was in Hospital because he picked up his cardiac grandpa. He randomly saw the doctor woman helping the kid and fall in crazy love. It makes sense that he killed the grandpa. The grandpa was the only man who knew how mentally ill the landlord is. So the landlord lived in fear that the grandpa can tell it to the doctor woman. The grandpa even knew that the also mentally ill father of the landlord killed his own wife and mother of the landlord. In the movie and old newspaper about the murder is shown. Sorry for bad english, I'm german.