Official sources said the manner in which a wristwatch was used as a timer to complete the bomb circuit to trigger the detonators kept on three newly-bought bicycles, two dustbins and a polythene bag was similar to the technique adopted by IM, which has links with terror groups in Pakistan.
Joint Commissioner of Pune City Police Sanjiv Singhal said 33-year-old Dayanand Patil, the lone person injured in the blast near Bal Gandharva theatre, was being 'interrogated'. He also said there has been no arrest or detention so far.
Patil's wife Satyakala and some bicycle shop owners in the city's Kasaba peth area were also questioned as part of the investigation. The police said Patil was not being treated as a suspect as of now but was being questioned by the police as to how the explosives found its way into his carry bag.
As investigators pieced together evidence, the sources said ammonium nitrate was apparently used to make the explosives with Neogel as a binding agent.
Four serial explosions in the space of less than one hour rocked a single area in the crowded Jangli Maharaj road on Thursday night. One explosive was partially detonated while another was defused, the sources said.
The investigators are not ruling out terror angle and trying to zero in on the outfit behind the blasts on a day when the new Home Minister Sushilkumar Shinde took charge. Shinde cancelled a scheduled visit to Pune in the evening before the explosions struck Pune.
Shinde said the Centre has taken the explosions "very seriously" and investigators were looking for clues. "We have taken it very seriously," he told reporters in New Delhi after a high-level meeting which reviewed the security situation in the country in the wake of the blasts.
The Maharashtra Anti-Terrorism Squad picked up for questioning the owner and an employee of a local shop in Pune from where two of the three bicycles were bought.
"A cycle showroom owner and his employee in Kasba Peth area have been picked up for questioning. We are hoping to get some concrete information from them," said an ATS official.
"We have first hand information that two of the three cycles have been purchased from this Kasba peth shop," the official said but did not reveal anything about the third bicycle.
Pune faced a major terror attack in February 2010 that killed 17 people and injured dozens more, including a number of foreigners, in the German Bakery, a restaurant popular with tourists.
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.
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 the ATS, city crime branch and central agencies."
Investigative agencies were searching for clues as the CCTV cameras installed at Dena Bank, McDonalds food outlet 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.
A team of the National Investigation Agency and experts of the National Security Guards have joined the investigation with the Maharashtra police to probe all angles.
The 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.