Source : Webster's Revised Unabridged Dictionary (1913)

Investigator \In*ves"ti*ga`tor\, n. [L.: cf. F. investigateur.]
   One who searches diligently into a subject.

Source : WordNet®

investigator
     n 1: a scientist who devotes himself to doing research [syn: {research
          worker}, {researcher}]
     2: someone who investigates
     3: a police officer who investigates crimes [syn: {detective},
        {tec}, {police detective}]