Green’s Dictionary of Slang

1. to beat, to injure, to kill.

1927		(con. 1918) J.W. Thomason Red Pants 111: Say, one guy was all set to massage your dome wit’ a table leg.
1928		Phila. Eve. Bulletin 5 Oct. 40/4: Here are a few more terms and definitions from the ‘Racket’ vocabulary: [...] ‘massage,’ to drub severely.
2002		(con. 1967) J. Laurence Cat from Hué 442: Of all the words American troops used to describe death in Vietnam — aced, blown away, bought it, croaked, dinged, fucked up, greased, massaged, porked, stitched, sanitized, smoked, snuffed, terminated, waxed, wiped out, zapped — the one I heard most was ‘wasted.’.

2. of the police, to beat up a suspect during an interrogation; thus massaging n.

1930

E.H. Lavine Third Degree (1931) 3: ‘Shellacking,’ ‘massaging,’ ‘breaking the news,’ ‘working on the ---,’ ‘giving him the works’ and numerous other phrases are employed by the police, throughout America and the world. [Ibid.] 59: The two gangsters, after receiving a massaging with pieces of lead pipe, were taken to the West Thirtieth Street police station.