Guwahati: A National Investigation Agency (NIA) special court here on Wednesday convicted four cadres of the National Democratic Front of Boroland's (NDFB) Songbijit faction for their involvement in the massacre of Adivasi villagers in Assam's Sonitpur district in December 2014.

The hearing on their quantum of sentence will take place on September 7.

The court held the four accused - Sanju Bordoloi alias Sibigiri, Bishnu Narzary alias N. Berema, Ahoy Basumutary alias B. Bujumbura and Nitul Daimary alias D. Naihab - guilty of opening indiscriminate fire and killing six persons and injuring two others in Santipur village under Rakhakmari police outpost in Sonitpur district on December 23, 2014.

Among the deceased was a 12-year-old girl, Bela Hemrom.

The other deceased were identified as Karna Hemrom, 25, Bhigi Bhanggra, 25, Sonamoni Hemrom, 50, Raju Kurmi, 30, and Kanab Hemrom, 34.

The NIA had registered a case at its Guwahati branch under Sections 120B/121/147/148/302 of the IPC, Sections 25 (1-A), 27 of the Arms Act and Sections 10/13/16/18/20 of the Unlawful Activities (Prevention) Act.

The NIA had filed the chargesheet on July 22, 2015, against the four.

Initially, this case was registered at Dhekiajuli police station but later, according to an order of the Union home ministry, the NIA took over the investigation.

This case was registered on the basis of a written complaint filed by Lokeshwar Marsha, a leader of the Assam Tea Tribes Students' Association.

The main accused, Sanju Bordoloi, who was the self-styled assistant organising secretary of the NDFB (S), was arrested from Bangalore on January 27, 2015. Subsequently, the other three accused were arrested from different parts of the state.

An official source said during the course of investigation of the case, one AK-56 rifle, three M-22 rifles and one HK-33 rifle were seized.

He said these arms were sent to Central Forensic Science Laboratory in Chandigarh for ballistic examination and the reports were placed before the court as evidence.