CBI named Sanju Bordoloi alias Sibigiri, alleged to be the Assistant Organizing Secretary of NDFB(S), Ajoy Basumatary alias B Buhum, Nitul Daimary alias D Naihab and Bishnu Narzary alias N Berama in the charge sheet, NIA said in a statement here.
In the charge sheet filed before a special court in Guwahati, NIA has asccused all the four under various sections of Indian Penal Code, Arms Act and Unlawful Activities (Prevention) Act.
During the course of investigation, NIA has been able to collect a "wide variety" of evidence ranging from oral testimonies to technical records and results from ballistic tests, the statement said.
NIA has opted to continue further investigation of the case since certain hardcore senior leaders of NDFB(S) are yet to be apprehended, it said.
After the attacks on Adivashis in Sonitpur and Kokrajhar districts of Assam, NIA's Guwahati branch had registered five cases in compliance with the orders of the Union Home Ministry. Out of these cases, charge sheets have been filed in three cases against 18 hardcore NDFB(S) militants.