The car was proceeding to Malappuram in Kerala on August 25 after collecting money for gold ornaments sold in Chennai when a five member van-borne gang, of whom three were in police uniform, intercepted the vehicle for a "search".
They ordered the four occupants to get into the van and two of their accomplices followed the vehicle in the car.
At a major road junction, the four were forced to get out and the gang escaped with the cash and car, which was later found abandoned at Thrissur in Kerala.
Police today said their investigation led to the arrest of three persons, who revealed the hand of police personnel in the robbery.
The trio also said that Rs two crore cash was taken by police and the balance distributed among them, police said.
The inspector was arrested earlier this week, police said, adding a hunt was on to nab another inspector and a head constable.
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