hatchet man vs murder one

hatchet man

noun
  • A male professional killer or gunman. 

  • A male who carries out brutal and unpleasant duties on behalf of another, such as firing dead wood employees. 

  • A male hatchet-wielding participant in a Chinese-American tong war. 

murder one

noun
  • murder in the first degree. 

How often have the words hatchet man and murder one occurred in a corpus of books? (source: Google Ngram Viewer )