Green’s Dictionary of Slang

1. (US) a burglar.

1953

E. Hemingway letter 26/27 Apr. in Baker Sel. Letters (1981) 820: No more mau-maus (burglars) since the last shootly-maru.

2. (US) derog. term for an African-American.

1968		J.Q. Wilson Police Behavior 196: [A] directive was sent to all [Oakland P.D.] officers ordering them to refrain from using language that ‘has a derogatory connotation’ in dealing with minority group members; specifically [...] black boy, black, shine, ape, spick, Mau Mau.
1975		E. Torres Carlito’s Way 116: That’s what I get for not keeping to my own kind. Between the mau mau uptown and the mafia downtown I’m in a sandwich.