Green’s Dictionary of Slang

thief and robber n.

(Aus.) a friend.

1905		Duke Tritton’s Letter n.p.: Dear China Plate, No doubt you have wondered how your old Thief and Robber has been doing since you went back to the Snake and Kidney.
1999		G. Seal Lingo 91: thief and robber is cobber.
2002		Pete’s Aussie Sl. Home Page 🌐 thief and robber: cobber (friend).