Green’s Dictionary of Slang

to betray; to give up someone to the authorities.

1839		Sydney Herald 13 May 2/3: Some free rascal takes a liking to, and marries a convict woman; he becomes tired, and wishes to get rid of her; he picks a quarrel with her, brings her before the Police, and ‘turns her in,’ as the slang hath it.
c.1854		Sam Cowell [perf.] ‘The Artful Dodger’ 🎵 t's all wery vell vhen you're in luck, / Your pals will stand a cup, / But vhen you're down they ‘keep you down’ / Because they ‘turns you up’.
1918		H. Simon ‘Prison Dict.’ in AS VIII:3 (1933) 32/2: TURN IN. 1. To report charges. [...] 2. To cause an escaped prisoner to be recaptured by betraying his whereabouts or identity to officers of the law.
1921		P. & T. Casey Gay-cat 193: They egg on the others an’ then toin them in fur the rewards.
1926		J. Black You Can’t Win (2000) 78: If either of you gets grabbed [...] and thinks he can get a light jolt by turning me in, he’s wrong.
1930		E.H. Lavine Third Degree (1931) 108: He had been persuaded by the detectives that he would be set free if he ‘turned up the gang.’.
1938		R. Chandler ‘Red Wind’ in Red Wind (1946) 55: He turned the gang in later.
1947		I. Shulman Amboy Dukes 4: Spotters who would turn you in for sleeping on the job.
1959		Murtagh & Harris Who Live In Shadow (1960) 53: What razor-legged obscenity went and turned me in?
1963		B. Hecht Gaily, Gaily 99: You turned me in to the cops, you bitch. You put me here to be hanged, you bitch.
1973		in C. Browne Body Shop 136: When the nurse found out about the reds she turned us in.
1980		(con. 1940s–60s) H. Huncke ‘Elsie John’ in Eve. Sun Turned Crimson (1980) in Huncke Reader (1998) 95: One of the cats he’d befriended got caught shooting up and when asked where he scored turned in Elsie’s name.
1991		B. Hamper Rivethead (1992) 133: Thank God, I thought, the crazy shit was gonna turn himself in.
1999		Guardian Guide 9–15 Oct. 98: His students turned him in for stripping during class and making obscene gestures.
2000		G. Pelecanos Shame the Devil 247: What’re you gonna do? [...] You fixin’ to turn me in?