Definition of a Flat Character = A character is is a person that doesn't change or grow in the story.
In the story we are seeing the story from his point of view. He's a character that is lonely with no one to love or love him back. Only people he considered his friends are the people he murders.
His story never changed he was a rude, evil killer BUT the story was made to make you sympathize with him or understand his ways and actions.
Once you see or read the story from the monsters point of view we see him as a intelligent creature with reasons as to why he is the way he is...
Either way he still remains a vicious killer from any point of view
Hope it helps..... It was a great read, Ill never forget that homework
