Green’s Dictionary of Slang

1. (also dead to the right) completely, absolutely; in context of an arrest or other form of apprehension, ‘red-handed’.

1859		Matsell Vocabulum.
1871		Galaxy 12 497: Once Goldstein got into the trouble which the police call being ‘got dead to rights,’ by which they mean being detected in a crime under circumstances which afford sufficient evidence to secure a conviction.
1885		Donaldsville Chief (LA) 26 Sept. 1/6: If they’d see us all coming out of a palace car, with linen dusters on, we’d have ’em so dead to rights that they’d throw up their hands and go to pieces before a ball was pitched.
1894		Mirror of Life 20 Jan. 43: [pic. caption] caught dead to rights.
1893		Independent (Footscray, Vic.) 7 Jan. 2/8: There’s the ball, dead to rights — see it, fellows?
1900		Nat. Police Gaz. (NY) 6 Oct. 6/1: [headline] sensational finish to the criminal existence of a gentleman crook / Caught Almost ‘Dead to Rights’ After the Burglary of a House in Mount Vernon.
1903		Argus (Melbourne) 1 Oct. 7/8: We were caught dead to rights.
1941		‘Digg Mee’ ‘Observation Post’ in N.Y. Age 19 July 9/7: ‘Parson’ Green came home [...] and caught his wife and Bill, dead to the right.
1996		(con. 1964-65) B. Thorpe Sex and Thugs and Rock ’n’ Roll 328: He’d confessed [...] and the Sarge had him dead to rights.
2019		D. Winslow Border [ebook] You have Eddie dead to rights on trafficking.

2. used as adj., complete, utter.

1913

‘Lord Ballyrot in Slangland’ in Tacoma Times (WA) 24 July 4/4: Ain’t he a dead-to-rights gent, filly?