Leaflets of the group carrying the call to establish Islamic rule in Bangladesh were found at most of the sites of the blasts.

Most of the bombs were kept in packets or bags but did not contain any kind of splinters or powerful explosives, said intelligence sources.

The bombs were hand-made and manufactured locally, said sources of a meeting of the intelligence agencies held after the blasts at the home ministry. The makers of the bombs were well-trained, the sources added.

"The bombs consisted of a simple circuit, couple of batteries, a switch, common gunpowder and sawdust," said Deputy Commissioner (DC) of Detective Branch (DB) of police Shahidul Islam.

The electric wiring was set in a manner so that the bombs do not explode mid-way, said another bomb expert, adding that there was a delay timer with each of the bombs that ignited the explosion after one to two minutes of activation. "This means at least one person was involved with each bomb," he said.

The time device made it possible to blast such a big number of bombs across the whole country within a short time, he said.

"The bombs made huge sound creating panic in the localities, but in most cases did not hurt anyone," said the bomb expert. The bombs were placed at unnoticeable spots of crowded public places which indicates the bombers did not mean to hurt anyone, he explained.