The bomb that went off at an Awami League office in Khulna city on Monday is similar to the Improvised Explosive Devices used in attacks on policemen at three spots in the capital between April and August.  

From the spot in Khulna, the investigators for the first time found an intact remote control circuit with an IED.

They say the bomb was powerful enough to kill people and cause destruction but its design was flawed.

In the previous attacks, the remote control circuits attached to the IEDs were found completely damaged.

The bomb disposal team of the Counter Terrorism and Transnational Crime (CTTC) unit has revealed this to The Daily Star after primary inspection of the spot in Khulna.

Additional Deputy Commissioner of the CTTC unit Rahmatullah Chowdhury, who coordinates activities of the bomb disposal team, told this newspaper that the explosives didn’t cause massive destruction as the materials used in the IEDs were insufficient to blow up the container.

Earlier on Monday, the IED exploded at the AL office in Khulna around 6:30pm, minutes after a bearded man wearing a cap left a bag there.

As in the previous incidents, the SITE Intelligence Group which tracks online activity of jihadist organisations and white supremacists, said early yesterday that the Islamic State claimed responsibility for the attack.

On September 23, the CTTC unit officials said a five-member cell of “Neo-JMB” was involved in the last five incidents in the capital. They also arrested two members of the cell.

The unit officials also claimed that they busted a bomb-making laboratory of the militant outfit in Narayanganj where the IEDs were made and supplied from.

About the latest blast, a high official of the CTTC unit said only a cell of “Neo-JMB” was dismantled through the arrest of the two in Narayanganj.

“We failed to trace the ‘ameer’, who used to control the cell,” he told The Daily Star, seeking anonymity.

“We suspect there are at least two to three other cells under the ‘ameer’ and one of those cells is responsible for the latest blast,” said the official.

Another CTTC unit official involved in the investigation said each of the cell has four to five members. But those cells don’t maintain contact with each other. They act on instructions from the “ameer”.

The official further said that like the previous five attacks in the capital, the blast in Khulna also took place after sunset and at the end of the month.

In the previous incidents, the target was police but this time the blast was carried out inside the AL office.

“We suspect that the cell members’ next possible target is the port city of Chattogram. We are trying our best to trace the ‘ameer’,” added the official.

Saiful Islam, deputy commissioner of the CTTC unit, said they would be able to give details of the Khulna blast after investigation.

Talking to this correspondent, Md Moniruzzaman, additional deputy inspector general of Anti-Terrorism Unit, said the IED was made using a battery, a connector, a remote device, a portable gas cylinder and a tape -- a trademark of “Neo-JMB”.

“We have got some clues and we are working on them,” he added.

No case was filed and no one was arrested, adds our Khulna correspondent.