Green’s Dictionary of Slang

(N.Z. prison) an inquisitive individual.

1999		D. Looser ‘Boob Jargon’ in NZEJ 13 29: detective n. Nosey person.
2001		D. Looser Boobslang [U. Canterbury D.Phil. thesis] 55/1: detective n. 1 a nosey, inquisitive person (frequently applied to prison officers as well as to inmates).