Investigators are looking for three men, two women and a child in connection with Monday's twin blasts in Mumbai that left 52 people dead and over 150 injured.

Mumbai blasts: The complete coverage

They are also probing the possible link of two Kashmiris to the blasts.

Investigators believe the blasts were carried out by some locals, in all probability members of the banned Students Islamic Movement of India, with possible assistance from some insurgents from Kashmir and logistical support from the underworld.

The complicated web of terror developing in the country has baffled intelligence agencies.

Based on preliminary information, telephone intercepts, eye-witness accounts and other inputs, the investigators now believe that the ones who planted the bombs in the two taxis that blew up in Zaveri Bazaar in Kalbadevi and near the Gateway of India are from Maharashtra, in all possibility from the Mumbai-Pune belt.

Till now, there is no concrete evidence to prove that the two blasts were coordinated, but "that is a possibility," sources said.

Independent terror modules carried out the blasts, the investigators are almost certain. They are also sure that the speculation that those who carried out the blasts were Gujarati Muslims is wrong.

Of the two militant sympathisers from Kashmir the investigators are looking for, one is a resident of Poonch. The other has been visiting Mumbai-Thane area frequently since June-July.

In fact, the Intelligence Bureau had issued alerts on the latter to the Mumbai police even before the blasts, say sources.

Officials said they expect some arrests in the "next couple of days" because they have been able to sketch out the details of  the group that hired the taxi that blew up near the Gateway of India.

Investigators believe that the RDX used in the blasts could have been procured only from Pakistan. Also, it would have been difficult to bring it to Mumbai "without the help of the underworld."

The web of terror that the central intelligence agencies are looking at comprises:

** ISI/terrorist groups in Pakistan, who provide RDX and other equipment to some underworld contacts that smuggle them to Mumbai.

** Motivators, the key hidden contacts, who create small and independent cells of local sympathisers.

** These cells are given specific instruction to collect material  from specified locations "and it is possible that they do not know much about those supplying the items."

Since these cells have very little information about the people assisting them and operate independent of each other, busting of one of them is no guarantee that there would be no more attacks.

"It is worse than fighting terrorism in Kashmir. In the Valley you are fighting a straight war with him. Either you kill him, or he kills you. You know your target," an officer said.

"You cannot target all members of a particular religion because someone amongst them is doing nasty things," said another officer.