death penalty vs manslaughter

death penalty

noun
  • A punishment in which the offender is put to death by the state. 

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 death penalty and manslaughter occurred in a corpus of books? (source: Google Ngram Viewer )