A wrist watch was used to trigger the explosives in the Pune coordinated serial blasts as evidence gathered by investigators on Thursday appeared to point to the involvement of home grown terror group Indian Mujahideen (IM).
Official sources said the manner in which a wrist watch 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.
Maharashtra ATS picked up the owner and an employee of a shop from where two bicycles used in Wednesday night's serial blasts in Pune were bought for questioning.
"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.
"We are not ruling out the possibility of involvement of Indian Mujahideen (IM) or right wing Hindu organisations," a senior police officer involved in the probe said on condition of anonymity.
Speaking to the media in Pune, Pune's joint commissioner of police Sanjeev Kumar Singhal said an FIR has been registered in the case against unknown people and no arrests have been made yet.
Singhal said 33-year-old Dayanand Patil, the lone person injured in the blast near Bal Gandharva theatre, was being 'interrogated'.
Patil 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.
"We are questioning him," Singhal said.
"He is a local and claims to have accidentally picked up the bag out of curiosity, opened it and got injured," he added.
Patil was discharged from Sasoon Hospital this morning but was taken into custody by the Pune Crime Branch for further questioning. His wife is also being questioned.
As investigators pieced together evidence, the sources said ammonium nitrate was apparently used to make the explosives with Neogel as a binding agent.
"We have registered a case 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," Singhal said.
Four serial explosions in the space of less than one hour rocked a single area in the crowded Jangli Maharaj (JM) road on Wednesday night. One explosive was partially detonated while another was defused, the sources said.
Explosives were strapped on two newly-bought bicycles which went off on the crowded Jangli Maharaj road.
Singhal said pencil cell batteries, timers and detonators have been found from the bomb sites and have been sent to the forensic science laboratory for testing.
"Sketches of suspected criminals are being made on the basis of information received from owners of cycle shops after a police team questioned them," Singhal said.
Four low-intensity blasts had rocked the city between 7.37pm and 8.15pm, leaving one injured.
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.
Meanwhile, security has been beefed up in Mumbai and other major cities of the state.
Road blocks have come up in different parts of the city, including the two national highways and approach routes from adjoining Thane and Raigad districts, while random checks on vehicles are being carried out.
On February 13, 2010, a powerful bomb had ripped through the popular German Bakery in Pune's Koregaon Park area, killing 17 people, including five foreigners, and injuring 60 others.
The explosion was later found to have been triggered by home-grown terror outfit Indian Mujahideen in co-ordination with LeT.
Maharashtra home minister RR 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 National Investigation Agency (NIA) and experts of National Security Guards (NSG) have joined the investigation with Maharashtra Police to probe all angles.
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.