As investigations progress into Wednesday's serial blasts in Mumbai, the police have started examining the role played by fringe elements of both the Indian Mujahideen as well as the Students Islamic Movement of India.
While the IM continues to be the main suspect in this attack, investigators are also looking into the possibility of involvement of radical members of the outlawed SIMI taking part in this attack.
Sources say that there is also a possibility that both these groups could have executed this attack jointly. The group has however been extremely careful while executing the attack, and preliminary investigations do not indicate any major interaction between members of this outfit while planning or executing this blast.
In the past, members of the IM and the SIMI have interacted through phones and also emails resulting in investigators catching on with them. However, this appears to be the handiwork of a very small group and it could have been planned by five to 10 persons of the same module.
"They have not communicated through phones, and it appears that the blasts were planned at one place and then executed," said a source.
A source from the Intelligence Bureau however added that they were probing the involvement of all possible groups.
"There are police teams in both IM and SIMI strongholds at the moment, and vital leads are being picked up from these places," added the source.
"Looking at the manner in which the bomb was made it becomes clear that it was assembled by a professional and not the module which had put together the bombs during the Delhi attack prior to the Commonwealth Games," the source added.
"They have used Improvised Explosive Devices, and the bombs were triggered off by a cell phone. However there is no trace of the phone yet," the source said.
Earlier, Union Home Secretary RK Singh also confirmed that the devices used in the blasts were sophisticated.