Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
perscrūtātor, ōris, m. [perscrutor], a thorough searcher, an examiner, investigator (post-class.): talium rerum, Capitol. Max. 1 (al. persecutor); Veg. Mil. 3, 3 (al. prosecutores); Cassiod. Var. 2, 15.