Detectives are baffled by Saturday's attempt to assassinate Leader of the Opposition and Awami League (AL) President Sheikh Hasina and frontline leaders of the main opposition party by raining grenades on her rally and firing indiscriminately at her vehicle.

The well-orchestrated explosions of high-powered grenades and the shooting to wrap them up in the heart of the capital, which left at least 18 killed and about 300 wounded, have taken some officials of the detective agencies completely by surprise.

Police retrieved two more grenades from the capital yesterday, one of them from a toilet of Gulistan Hawkers' Market near the very site of Saturday's explosions. An army team of explosives experts took them away at around 11:30am.

The other one was found in a drain of Dhaka Central Jail in the morning and the shocking discovery has baffled detectives involved with investigations into other bomb blasts in the country. They even asked The Daily Star correspondent to tell them who are behind the deadly blasts and with what motive, if he stumbles onto behind-the-scene facts.

The security officials, speaking on condition that they not be named, said about Saturday's blasts that it would have been impossible for one group to throw grenades from the rooftops of nearby buildings and the other one to fire indiscriminately at the AL chief at the same spot and same time unless the assailants were well-trained.

"It is certain that the assassins were split into several groups and took position in different places and a group was coordinating their teams," one of the officials who visited the spot of the blasts said.

They are desperately looking for leads to the masterminds and source of the grenades. The investigators are also thinking of looking into the possible links of the killers of Bangabandhu Sheikh Mujibur Rahman to the attacks after the discovery of the grenade on the Dhaka Central Jail premises.

Colonel (Dismissed) Farukur Rahman, Colonel (Dismissed) Sultan Shahryar Rashid Khan, Colonel (Dismissed) Bazlul Huda and Colonel (Retired) Muhiuddin are now in the central jail.

The investigation officer of the murder case filed in connection with Saturday's killings, Sub-Inspector Amir Hossain said told The Daily Star," We have got no clue to the incident and there has been no progress in the investigation. All detective agencies are working on the case."

"Nothing can be said for certain, too many possibilities are there but we are looking into the possibilities of whether the assassins of Bangabandhu have had new plans," said another security official, wishing anonymity.

The official argues that most of the well-trained killers of Bangabandhu are now abroad and only a handful of them are in jail. Again, most of his killers also stand accused in the jail-killing case, the verdict of which is scheduled to be delivered on September 7. He believes Bangabandhu's killers may have carried out the attack on the AL chief and its top leaders for the sake of their survival.

"How on earth did the grenade make its way to the central jail? Some of the killers of Bangabandhu are staying there. Maybe there was a plan to bring out the killers by exploding the grenade and creating chaos and confusion in the jail, " another security official notes.

He said Bangabandhu's assassins have close ties to some countries and it is possible for them to smuggle sophisticated arms and hand-grenades into the country from these countries.