hangman vs official killer

hangman

noun
  • Someone responsible for hanging pictures and other artworks in a gallery, museum etc. 

  • An executioner responsible for hanging criminals. 

  • A guessing game where one has to guess the word an opponent is thinking of by guessing one letter at a time, and involving the gradual drawing of a stick figure hanging from the gallows. 

official killer

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