Immediately after his surrender at East Shaplabagh in this north-eastern divisional city yesterday morning, the law enforcers investigating into militancy termed the catch a big success in dealing with the Islamist terrorism menace.

"There's no doubt that he holds keys to many important things. But, we'll be able to say the exact extent of his usefulness in uncovering the mysteries only after interrogating him thoroughly," Rapid Action Battalion (Rab) intelligence chief Lt Col Gulzar Uddin Ahmed told these correspondents at Rab-9 headquarters, after Rahman had been brought there following his surrender.

The four members of Majlish-e-Shura, the 7-member highest decision-making body of Jama'atul Mujahideen Bangladesh (JMB), arrested so far have all named Rahman as the man who knows every detail of the banned Islamist militant outfit, Gulzar mentioned.

So, he hoped the JMB supremo would provide them with vital information about the August 17 terror strike and the militant networks both in and outside the country.

A Sylhet court yesterday placed Rahman on a 10-day Rab remand in a case filed under the Explosives Substances Act with Kotwali Police Station. He was then sent to Dhaka, where an intelligence task force is now interrogating him in Rab custody.

Gulzar, who is on the 6-member high-powered government committee probing into the August 17 countrywide bomb attacks, said their next course of action will concentrate on netting the three JMB Shura members still at large. They are Siddiqul Islam alias Bangla Bhai, close associate of Rahman and operations commander of another banned militant organisation Jagrata Muslim Janata Bangladesh, Salahuddin alias Salehin, in-charge of Sylhet-Mymensingh region, and Faruq Hossain alias Khaled Saifullah, commander of the greater Rangpur-Dinajpur region.

According to well-placed sources, Salahuddin visited Sylhet recently. It was from his visit that the law enforcers got the clue that Rahman might be hiding in this area. They verified the clue with information received from other sources. After scrutinising the call-list in the cellphone of Hafez Mahmud, arrested last Tuesday in the capital's Baitul Mokarram area, they finally were sure that Rahman indeed was hiding in Sylhet, somewhere at Shaplabagh.

The three JMB Shura members arrested before Rahman are his brother Ataur Rahman Sunny alias Sajid, regional commander of Dhaka, son-in-law Abdul Awal Sarker alias Adil alias Ashiq alias Arafat, commander of the greater Rajshahi region, and Rakib Hasan Rasel alias Hafez Mahmud, Khulna regional commander.

Investigators said these three arrestees said they did not know much about the JMB network and operations, and so could not come up with some vital information the cops are looking for.