vestigator
From LSJ
vestīgātor: or vestīgĭātor, ōris, m. vestigo,
I a tracker, spy, tracer, searcher (not in Cic.): vestigator a vestigiis ferarum, quas indagatur, Varr. L. L. 5, § 94 Müll. (where the read. is vestigiator); so Col. 9, 8, 10; Sen. Ben. 3, 26, 2; Dig. 33, 7, 12, § 12.