The ATR-42 is a small turbo-prop plane.
It stores baggage next to the lavatory as you can see in the far right portion of these three cabin layouts.
They say a passenger then created a story about being ill in order to avoid suspicion for the time he spent in the lavatory working around the panels to access the bags; by the end of the flight be managed to pocket $238K. Illness was also used as a distraction for his escape. His travel companion asked for an ambulance to be called to the runway. When it arrived the thief declined and walked away from the commotion.
This story illustrates how a classic social engineering method — reverse-good Samaritan — will help an attacker deflate suspicion.
Although it has believable elements, I find several parts surprising. The passenger knew the bags held cash, knew how to access them in a private space away from the guard, and that bags of nearly $2 million were not booby-trapped (e.g. exploding ink) or tamper-proof. The incident was detected, for example, by the cleaning crew who found a bag of money left behind in the lavatory.
Those parts together, assuming this story is true, suggest an inside job involving Brinks staff, like one from last year.
Comerica says it did not discover the shortfall until several weeks later. When it did, it says, both Brink’s and Garda investigated and found that the “cash bag showed signs of tampering” and that the “Brink’s teller who processed the cash bag noticed that [it] was compromised but did not report that fact.”
When the bag got to Brink’s, it contained only $117,000 and was missing “a general ledger entry from Comerica’s banking center,” according to the complaint. The bank adds that instead of reporting the shortage, a Brink’s employee altered the paperwork.