Five months after a builder in south Delhi made a complaint about an extortion call from an alleged gangster, the Delhi Police on Sunday said they have arrested a decorated assistant sub-inspector of their own force for masterminding and facilitating the crime.

The ASI, 48-year-old Rajbir Singh, allegedly passed on the builder’s phone number to the gangster and even advised him to shoot at his son’s car to scare them into paying up.

The police had arrested the alleged gangster and three other suspects previously as part of their investigations, which eventually led to Singh’s role being revealed.

The police did not reveal the builder’s name to protect his privacy.

Singh had, in 2005, been conferred with the President’s Police Medal for Gallantry, as well as the Asadharan Karya Puraskar (award for extraordinary work) seven times, and also received an out-of-turn promotion in 2015. The police, in a statement released on Sunday, said they were contemplating dismissing him from service and examining the possibility of withdrawing the medals conferred on him.

Atul Kumar Thakur, deputy commissioner of police (south), said the sequence of events, which culminated in the ASI’s arrest, began on June 28 when the builder received an extortion call for Rs 2 crore. “The caller introduced himself as gangster Kaala and threatened to eliminate his family if he didn’t pay Rs 2 crore,” Thakur said.

The victim approached the police, who registered a case at Hauz Khas police station.

Investigations revealed that the phone number used to make the extortion call was snatched in Rohtak in Haryana the previous evening. The SIM card was removed from that phone and inserted into another handset to make the call, the police said.

Within the next month, the police arrested three suspects — Mukesh, Sawan and Sunny — and recovered three mobile phones from them.

In August, the police arrested Kaala, an alleged criminal who works out of Rohtak.

Meanwhile, as the police analysed call records from the seized phones, they found that ASI Singh had been in regular touch with Kaala and the other suspects before and after the extortion calls were made, said the DCP. “He had also met them extortionists a few times,” the officer added.

The police then began focusing on Singh’s role and found that he knew the builder for at least 10 or 12 years.

“After the extortion calls, on July 14, Singh had also called the builder to speak to him about the crime and offer help. But he was actually trying to gauge his mood and the situation,” Thakur said.

The police then questioned the arrested suspects, who allegedly disclosed that the policeman was the mastermind. “Singh had passed on the builder’s phone number to Kaala to make the extortion calls,” Thakur said.

When the builder did not pay, the ASI had also allegedly advised Kaala to shoot at his son’s car, an attack that eventually did not take place.

“The ASI has denied making such a suggestion, though there is enough evidence against him for planning the crime and getting it executed,” said another police officer who didn’t want to be identified.

Singh was arrested on Friday, until which point he was posted in the south-west zone of the police control room.

“The Delhi Police is examining the possibility of withdrawal of medals conferred upon him. He has been suspended and proceedings for his dismissal are being contemplated,” read a statement released by the force.