pickpocket vs stool pigeon

pickpocket

noun
  • One who steals from the pocket of a passerby, usually by sleight of hand. 

verb
  • To pick pockets; to steal. 

stool pigeon

noun
  • An informer to the authorities, especially one who gives up criminal associates. 

  • A pigeon tied to a stool by a piece of twine, used as a decoy to entice free-flying birds to the ground to be shot or trapped. 

How often have the words pickpocket and stool pigeon occurred in a corpus of books? (source: Google Ngram Viewer )