noun (n)

• a scientist who devotes himself to doing research(noun.person)

  Synonym:
  research worker, researcher
  

  source: wordnet30
• someone who investigates(noun.person)

  source: wordnet30
• a police officer who investigates crimes(noun.person)

  Synonym:
  detective, police detective, tec
  

  source: wordnet30
• One who searches diligently into a subject.(noun)

  source: webster1913