Green’s Dictionary of Slang

(US Und.) one who assesses a property as a target for burglary.

1949		H. Wilson ‘I Was King of the Safecrackers’ in Hamilton Men of the Und. 138: The reports from our many casers were neatly typed out.
1955		‘Blackie’ Audett Rap Sheet 84: Eddie Bentz was the best caser and get-away planner in the business.
1970		‘Red’ Rudensky Gonif 94: After checking newspapers, talking with casers for Dinty’s mob and spending six weeks just scouting around, we were beginning to feel the pinch.