BENGALURU, Dec. 15 -- When the men stopped the cash van on a Bengaluru road on the morning of November 19, they looked official enough to raise no alarm. Dressed with confidence and flashing documents that resembled credentials from the Reserve Bank of India (RBI) and the Income Tax Department, they told the crew they were acting on orders. Within minutes, nearly Rs.7.11 crore had vanished.

What stunned investigators was not just the scale of the robbery, one of the largest daylight cash heists in Bengaluru's recent history, but who was allegedly involved. As the inquiry unfolded over the next 60 hours, the trail led back inside the police force itself.

A serving police constable attached to Govindarajanagar police station was identifie...