Peach

Verb.

2 . Transitive verb: to inform against: betray.

Intransitive verb: to turn informer.

[Origin: Middle English pechen, short for apechen to accuse, from Anglo-French apecher, empecher to ensnare. A shortening of appeach, an obsolete variant of impeach. Related: Peached; peaching. ]

(1560)

“I have the cabman who took you to Whitehall and the cabman who brought you away. I have the commissionaire who saw you near the case. I have Ikey Sanders, who refused to cut it up for you. Ikey has peached, and the game is up.” – The Adventure of the Mazarin Stone, The Case-Book of Sherlock Holmes – Arthur Conan Doyle.

While James Cagney never actually said the line “you dirty rat”, I can hear his voice in my head, saying “you dirty, rotten peach!”