The ULFA general secretary has been in jail in Bangladesh since 1997 after his arrest for various offences, including illegally staying in the neighbouring country.
Both Subrata Bain and Sajjad Hossain were handed death sentence by Bangladeshi courts for murder and grenade attack on an Awami League rally in Dhaka.
Bain was arrested in Kolkata last year, 18 days after his escape from a jail in Nepal.
