The court in Kishoreganj sentenced ULFA leader Ranjan Chowdhury alias Major Ranjan and his Bangladeshi aide Pradip Marak who were arrested in July, 2012 from Lakhsmipur area of Bhairab with a number of weapons in their possession.
Chowdhury had been staying in Bangladesh since 1997 and maintained contact with the group, the police had then said.
A pistol, a revolver, four rounds of ammunition and four grenades were seized from them.
Four cases were filed against them under the Arms Act, Explosives Substances Act, illegal immigration and anti-terrorism acts.
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Chowdhury was found guilty on both counts, while Marak was acquitted in the case under the arms act.
Chowdhury, who is married to a Bangladeshi woman, has been making frequent trips to India on organisational purposes, Dhaka Tribune reported.
Ranjan illegally entered into Bangladesh through Kurigram district in September 1997 to meet ULFA military wing chief Paresh Barua in Dhaka.
United Liberation Front of Asom (ULFA) operatives under Ranjan's leadership were active in Sherpur, Kurigram and Sylhet, the bordering districts of Assam.