Green’s Dictionary of Slang

peter v.2

[peter n.5 (1)]

(US) to use knockout drops on a victim.

[US]Maurer & Vogel Narcotics and Narcotic Addiction in Maurer Lang. Und. (1981) 326/2: peter. [...] 2. the racket of robbing people (addicts, drunks, customers of a prostitute, etc.) by the use of chloral hydrate.