Rab took up the case as per a directive from the Home Ministry, according to sources in Khulna Metropolitan Police (KMP).

Sabbir was arrested by Rab Thursday night from Tootpara under Khulna thana. The case was filed with Daulatpur thana Friday night under the Explosives Substances Act.

The investigation by Rab will begin today after the Investigation Officer (IO) Sub Inspector Ajit Kumar Majumdar of Daulatpur thana hands over the case docket.

The arrested JMB leader handed over to Rab was taken on five days' remand on Saturday for interrogation in connection with the recovery of a huge quantity of explosives from his possession and his involvement in the August 17 serial bomb blasts last year.

This will be the first case in Khulna against an Islamic militant to be investigated by RAB on orders from Home Ministry, the sources said. The government has taken seriously the explosives haul. The militant (Sabbir) supplied 34 bombs to JMB cadres in three districts for attack on specified targets, the sources said.

Sabbir who is also an 'ehsar' (leader) of JMB told police during interrogation on the second day of remand on Sunday that he rented a room at 'Jessore Chatrabash' (students' mess) at Daulatpur to hide the explosives and stayed there along with 12 other cadres including four 'ehsars'.

But all of them left the mess on August 21 last year to escape arrest, Sabbir said.

Sabbir is yet to disclose the source of explosives and other materials for making bombs and grenades, said Zahur Chowdhury, Assistant Police Commissioner of KMP Detective Branch.

Mentionably, a total of 22 JMP leaders and cadres have so far been arrested from different areas in Khulna city and district since the August 17 serial bomb blasts. Of them, four were arrested by Rab and 18 by police.

The four arrested by Rab are all 'ehsars' of JMB. They are Sabbir, Matiur Rahman alias Masud, Abdur Rakib alias Nooruddin and Ismail Hossain alias Habib.