first-degree murder vs manslaughter

first-degree murder

noun
  • 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. 

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

manslaughter

noun
  • The unlawful killing of a human, either in negligence or incidentally to the commission of some unlawful act, but without specific malice, or upon a sudden excitement of anger; considered less culpable than murder, but more culpable than justifiable homicide. 

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