The mystery behind the October 1 serial blasts in Agartala that left 100 injured has been solved with the police zeroing in on the outlawed All Tripura Tiger Force and arresting the mastermind, the CID said on Wednesday.

Two arrested overground ATTF activists Shanti Debbarma and Angad Santhal first provided the lead during interrogation that 25-year-old Bikash Debbarma belonging to the outfit masterminded the blasts, CID sources said.

Based on the information provided by the duo, the police raided a rented house on October 11 at Bhati-Avoynagar in Agartala and seized bomb-making material and the cover of the SIM cards used in the blasts, but Bikash had already escaped.

He was subsequently arrested from Khowai in West Tripura district on October 13, the sources said.

Bikash and another insurgent of the ATTF were trained by the Bangladesh Rifles and DGFIi, the intelligence wing of the Bangladesh Army, at Munshighat, near Chittagong two months ago, the sources said.

The explosives used were supplied from ATTF base camps in Sylhet district. They were transported by a collaborator of the ATTF from Sidhai area, bordering Sylhet, 40 km from Agartala, and taken to the house rented by Bikash, according to the sources.

Bikash used a mobile phone to trigger the blasts himself, the sources added.