investigation (n.) Look up investigation at Dictionary.com
early 15c., from Old French investigacion (14c.), from Latin investigationem (nominative investigatio) "a searching into, a searching for," noun of action from past participle stem of investigare "to trace out, search after," from in- "in, into" (see in- (2)) + vestigare "to track, trace," from vestigium "footprint, track" (see vestige).