Making a breakthrough into the May 15 Guwahati grenade blast, the police on Tuesday arrested former President of Post Graduate Students 'Union (PGSU) of Gauhati University Sanjib Talukdar.

"On the directives of ULFA (I) Commander-in-Chief Paresh Baruah, the former student leader took Bijoy Asom and Papu Koch on a tour of the Guwahati city prior to the blast," police said, adding, "Sanjib Talukdar was in constant touch with the ULFA (I) chief.

It was also informed by the police that prior to the blast, Paresh Baruah had long telephonic conversations with Sanjib Talukdar.

Talukdar was the PGSU president from 2016 to 2017.