Green’s Dictionary of Slang

to find prospective victims for a confidence trick or similar crime; thus locator n., one who carries out such searches.

1928		M.C. Sharpe Chicago May (1929) 261: Locating — getting prospects.
1931		J. Wilstach Under Cover Man 92: ‘Me, I can’t locate,’ he complained, ‘so I’m goin’ to pay a finder.’.
1938		J.E. Hoover Persons in Hiding 149: Kathryn had an underworld reputation as a ‘locator,’ or ‘caser,’ the person who goes ahead to plan the robbery of a store or bank.