culpable homicide vs first-degree murder

culpable homicide

noun
  • Homicide which is culpable but does not rise to the level of murder; unlawful killing of a human being which does not constitute murder. 

  • Used other than figuratively or idiomatically: see culpable, homicide. 

first-degree murder

noun
  • An act that constitutes the crime of first-degree murder. 

  • The criminal offence of murder in a form considered by law to be the most serious; the precise distinction may vary by jurisdiction but typically involves premeditation, or the choice of victim or other circumstances being regarded as especially blameworthy. 

How often have the words culpable homicide and first-degree murder occurred in a corpus of books? (source: Google Ngram Viewer )