case officer vs custodian

case officer

noun
  • A person assigned to manage a client's affairs. 

  • In intelligence organisations, a person who manages a network of agents. 

custodian

noun
  • A person entrusted with the custody or care of something or someone; a caretaker or keeper. 

  • a janitor; a cleaner 

How often have the words case officer and custodian occurred in a corpus of books? (source: Google Ngram Viewer )