Green’s Dictionary of Slang

case n.5

[case v.1 (1)]

a surveillance, a look around.

[US]Irwin Amer. Tramp and Und. Sl. 48: Case. — [...] An observation or spying.
[US]Monteleone Criminal Sl. (rev. edn).
[US]M. Spillane Return of the Hood 8: Newbolder’s quick case of the place didn’t make them.