In this picture it shows that the old man had a "vulture" eye which disturbed the caretaker which on a daily bases he would plan a way to kill the old man.
During the middle of the story the caretaker was so disturbed by the old mans eye that he decided to murder him during the night, as shown in the picture.
Because of what he did, he of course was insane. The only way for him to not get in trouble was to hide the body but because of him feeling guilty he got caught in his crime. Making the message of the story to be that your actions have consequences.