Green’s Dictionary of Slang

string up v.

to garrotte.

1885		Ledger (Noblesville, IN) 14 Aug. 6/2: string up — to garrotte.
1931		O. Strange Law O’ The Lariat 177: If he won’t talk, string him up.
1937–8		Doc Quinn [ex slave] in Yetman Voices from Slavery (1970) 245: Dat evenin’ five Negroes jumped from de bushes [...] and proceeded to string me up by de neck. I hollers as loud as I could, [...] and de election officers, just happened to be comin down de road and hear me yell. Dey run off de niggers.
1947		‘F. Bonnamy’ Self Portrait of Murder (1951) 15: Since he’s twice as big as an ordinary human, I figure even convalescent he could string up O’Donnell.
1950		Goldin et al. DAUL 214/1: String up. [...] 2. To hang; to lynch; to commit suicide by hanging.
1981		(con. c.1900s) A. Harding in Samuel East End Und. 106: In the back alleys there was garotting – some of the brides would lumber a seaman while he was drunk and then he would be dropped – ‘stringing someone up’ was the slang phrase for it.
1998		B. Robinson Peculiar Memories of Thomas Penman 46: Hang the Irish . . . he could solve the Irish problem overnight . . . get into Dublin and string up some Micks.