As a student, Sarbananda Sonowal, 53, was at the forefront of the AASU-led agitation against illegal immigrants in Assam. It was also his petition that prompted the Supreme Court to declare the IMDT Act unconstitutional in 2005. After taking over as CM last month, Sonowal vowed to seal the Bangladesh border within two years. He spoke to Dola Mitra. Excerpts: