The Collaborative International Dictionary of English v.0.48:

Investigative \In*ves"ti*ga*tive\, a.
   Given to investigation; inquisitive; curious; searching.
   [1913 Webster]

WordNet (r) 3.0 (2006):

investigative
    adj 1: designed to find information or ascertain facts; "a fact-
           finding committee"; "investigative reporting" [syn:
           fact-finding, investigative, investigatory]

Moby Thesaurus II by Grady Ward, 1.0:

23 Moby Thesaurus words for "investigative":
   analytic, curious, examinational, examinatorial, examining,
   explorational, explorative, exploratory, fact-finding, feeling,
   groping, heuristic, indagative, inquiring, inspectional,
   inspectorial, investigational, investigatory, questioning,
   tentative, testing, trying, zetetic