Patna, Jan. 2 -- On November 21, a passenger stepped off a train at Howrah, lighter by gold biscuits worth Rs.1.44 crore that he had left with 14 hours ago. The men who took it allegedly wore police uniforms, he told the authorities. Initially, the case seemed routine - one of thousands of robberies that unfortunately blight the railways in India.

A month on, however, investigators have arrested the man who was supposed to be in charge of solving the crime, the station house officer of the GRP police station.

Rajesh Kumar Singh's arrest has turned the robbery on its head, recasting it from a case of rogue constables to what officers now say was a carefully coordinated operation involving policemen and civilian insiders.

On November 20,...