The probe suspects an Indian Mujahideen (IM) imprint on the terror attack. The blasts were executed around seven months after two alleged IM operatives---Sayed Maqbool and Imran Khan ---surveyed the stretch on the directions of the terror outfit's co-chief Riyaz Bhatkal on a motorbike.
The investigators are also examining CCTV footages procured from the two blast sites to zero in on the perpetrators. The available videos have captured the moments before and after the blasts. "It was evening and the sites were very crowded - two factors which make the task of sifting through the footages tough," said another investigator, requesting anonymity.
The investigators are not ruling out the possibility that the bomb planters could have come from outside the city and have put suspected IM operatives hailing from a few states including Maharashtra under the scanner. "In a bid to evade detection, the perpetrators could have used operatives from outside the city. We suspect IM operatives from Nanded or surrounding districts could have been used," said the investigator. Both Maqbool and Khan were active in Nanded before their arrest by Delhi police's Special Cell in October last year for their alleged involvement in executing the August 2012 Pune blasts.
Forensic analysis of the debris found at the blasts sites have established that nitrate-based explosives, packed in metal containers with shrapnel, were used along with timers.
Meanwhile, the home ministry has issued a nation-wide alert to maintain a strict vigil at all those places which were recced by IM operatives.