One man, said to be a former member of the Kamtapur Liberation Organisation (KLO), was Sunday arrested in connection with the bomb blast in West Bengal's Jalpaiguri that claimed six lives, police said.
Chandan Roy was arrested from Moynaguri area of Jalpaiguri district, said police.
Superintendent of Police Amit P. Javalgi said some others were being detained for interrogation.
Police were taking the help of various agencies in the interrogation, he added.
"The probe is proceeding in the right direction," he said.
Denying its involvement in the blast, the KLO Friday warned police against defaming the outfit.
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Police suspected involvement of the KLO behind Thursday's explosion caused by an improvised explosive device (IED) in Bajrapara area.
Forensic experts have visited the explosion site, while security has been increased in and around north Bengal.
A National Investigation Agency (NIA) team too inspected the site and collected samples.
The KLO has been demanding a Kamtapur state comprising six districts - Cooch Behar, Darjeeling, Jalpaiguri, North and South Dinajpur and Malda - of West Bengal and four contiguous districts of Assam - Kokrajhar, Bongaigaon, Dhubri and Goalpara.