In the film The Sting, the woman who pickpockets the gang boss, Lonnegan, is actually a con artist named Loretta Salino, and she's integral to the larger scheme orchestrated by Johnny Hooker and Henry Gondorff. She's not acting independently; instead, her pickpocketing is a key part of setting up the big con. Loretta steals Lonnegan's wallet, which contains a crucial piece of planted information: betting slips that appear to show Hooker is getting winning information on horse races in advance.
Loretta's theft, seemingly innocuous at first, is deliberately designed to pique Lonnegan's interest and make him believe Hooker possesses privileged knowledge about upcoming horse races. By successfully "lifting" Lonnegan's wallet, she creates the initial hook that draws him into the fraudulent betting scheme. This carefully staged event is essential to manipulate Lonnegan's greed and confidence, leading him to believe he can exploit Hooker's "inside" information for a massive payout. Without Loretta's successful pickpocketing operation, the entire elaborate sting would never get off the ground.
The summary misidentifies Billie (the pickpocket) as Loretta Salino (the assassin).
The summary invents a plot device (planted betting slips) rather than explaining the actual mechanism (creating a debt to force a private conversation).