homicide vs serial killer

homicide

noun
  • The killing of one person by another, whether premeditated or unintentional. 

  • The department within a police force that investigates cases of homicide. 

  • A person who kills another. 

  • A victim of homicide; a person who has been unlawfully killed by someone else. 

serial killer

noun
  • A person who commits multiple (more than two) murders, especially similar ones with no obvious motive over a period of time with a "cooling-off" period between each murder. 

How often have the words homicide and serial killer occurred in a corpus of books? (source: Google Ngram Viewer )