A team of National Investigation Agency and experts of National Security Guards have joined the investigation with Maharashtra Police to probe all angles to determine whether any terror outfit was behind the blasts in the city last night.
Investigative agencies were searching for clues as the CCTV cameras installed at Dena Bank, McDonald's and Bal Gandharva traffic square, near where the explosions occurred, have not yielded any evidence so far and some of them were non-functional, sources said.
They said the Maharashtra ATS, city Crime Branch and the NIA are looking for clues from the two bicycles as two of the four coordinated blasts last night occurred in their front carriers.
Explosives were strapped on these bicycles which appear newly purchased and investigators are trying to locate the shop from where these were bought in order to nail the perpetrators.
As reports said a black sticky substance with ammonium nitrate was used in the explosions, forensic experts are also trying to ascertain the concentration of explosives in the devices to zero in on the likely group behind the blasts.
According to sources, different terror groups use varied concentration of explosives in their "signature bombs". Reports have said battery operated detonators with digital timers could have been used to trigger the blasts.
Home Minister Sushil Kumar Shinde said in New Delhi that the Centre has taken the near simultaneous explosions "very seriously" and investigators were looking for clues.
"We have taken it very seriously," he told reporters here after a high-level meeting which reviewed the security situation in the country in the wake of last evening's blasts in Pune.
Dayanand Patil, the only person injured in the blast at Bal Gandharva Theatre square, is being questioned by police as to how the explosive found its way into his carry bag.
Sources said Patil, who sustained minor injuries, was not being treated as a suspect in the case. Patil has told the police that he had visited the dharna by Anna Hazare's India Against Corruption and somebody kept the explosive in his carry bag. The explosion occurred when he tried to open a box in which the explosive was kept.
Police have registered an offence against "unknown persons" under sections 307 (attempt to murder), 427 (mischief causing damage), 120 B (criminal conspiracy) and relevant sections of Unlawful Activities Prevention Act and Explosive Substances Act.
Pune Commissioner of Police Gulabrao Pol had yesterday said as very low-intensity explosives were used in the blasts, it did not appear to be the handiwork of terrorists and could be an act of mischief.
However, Union Home Secretary R K Singh said in Delhi that terror angle could not be ruled out as the blasts occurring minutes apart were a coordinated act.
Maharashtra Home Minister R R Patil, who visited the blast site, said, "Whether it was a terrorist act or not will be determined only after proper investigations are carried out by Maharashtra ATS, city crime branch and central agencies."
Unconfirmed reports said ammonium nitrate could have been the substance used in the blast triggered by small detonators and pencil cells.
Earlier Union Home Secretary R K Singh said in Delhi that forensic experts were examining the two unexploded IEDs and nature of the four blasts. "Since the blasts have taken place within an area of 500 metres and within a span of 45 minutes, it appears to be a coordinated act. I am sure there was a plan behind it," he told reporters here.