the.com/inside job

means A theft, fraud, or sabotage carried out with the help of someone who belongs on the inside — an employee, insider, or trusted party — rather than an outside intruder.

from Straightforward compound coinage from American crime slang, rising in print in the early 1900s alongside terms like 'con job' and 'con man.' 'Inside' marks the crucial detail: the perpetrator had legitimate access — keys, codes, trust — unlike a break-in from outside. 'Job' had already long meant a criminal undertaking (a 'bank job,' a 'heist job'), a sense traced back to 17th-century English usage of 'job' as any piece of work, criminal or not. The phrase caught on in detective fiction and newspaper crime reporting, where the twist that the thief had help from within was the whole point of the story.