In the age of cellphones and emails, a gang engaged in extorting contractors banked on services of an unofficial postman — an aide of the kingpins — to deliver threat letters without any evidence.

Deadly duo Mantu Sharma and Sambhu Sharma might be behind bars now after literally ruling over the contracts of the Central Public Works Department (CPWD) for 13 years, but their “postmen” are on the job, still threatening contractors. Police apprehended 22-year-old Gobind Singh, a resident of Muzaffarpur and a confidant of the duo, late on Tuesday evening during a routine checking drive on the Ashiana-Digha Road within Rajiv Nagar police station limits.

Sources told The Telegraph that the duo, especially Mantu alias Pradumna, who was arrested by the Bihar Special Task Force (STF) from Lucknow in January this year, used to write letters from prison and hand them over to their trusted aides such as Singh for being delivered to the CPWD Class I contractors.

Mantu is at present lodged at Bhagalpur Central Jail. Sambhu was shifted to Beur Central Jail on Wednesday from Buxar Jail.

Confirming the arrest of Singh, the aide of Sharmas, a police officer told The Telegraph: “The police were on a checking drive when Singh tried to escape after seeing the men in uniform. He was chased and arrested. A loaded pistol was recovered from his possession. He is a big catch. Singh, a native of Muzaffarpur, is a criminal and the right hand man of the two gangsters languishing behind bars now. Interrogations revealed something quite unique. This man used to work as a postman for Mantu.”

The officer said as the cellphones of Mantu and Sambhu as well as most of their gang men were always under surveillance, letters were the best way to communicate the threats.

“Singh and Mantu both hail from Muzaffarpur. The police have information that there are many such henchmen of the duo who are now moving to other contractors as postmen. This is a new way to keep the business running,” the officer said.

Sambhu is a resident of Chhapra.

“Mantu was arrested in January. Sambhu was arrested sometime later. The gang’s network is very strong and have contacts of all the CPWD contractors,” said the officer.

The gang of Sharmas, operating since 2001, murdered some contractors who refused to pay the commission demanded by the duo. The Sambhu-Mantu gang, which had shifted base from Bihar to Uttarakhand and to Delhi later, is active since 2001. The gang consists of highly trained sharpshooters.