Pune police have however, detained four people including the sole injured victim Dayanand Patil, a tailor. The others are Patil's wife Satyasheela and Balu and Chintu Deshmukh - two brothers who own Sony Cycle Trading Co - the shop from where the cycles used in the blast were purchased.
Confirming the development, Pune Police Commissioner Gulabrao Pol said that Balu and Chintu are detained for questioning after they confirmed that an unidentified person purchased two bicycles from their shop Wednesday morning.
Earlier speaking to media persons here, 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.
Patil, who was the only person injured in the blast, is suspected to have been linked in the incident and is being interrogated. "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.
"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.
Patil was discharged from Sasoon Hospital this morning but was taken into custody by the Crime Branch, which is investigating the case, for further questioning.
Police sources claimed that Patil possesses a passport and has travelled to Jordan in 2003, but officials refused to confirm this.
Singhal also said pencil cell batteries, timers and detonators had been found from the bomb sites and have been sent to the forensic science laboratory for testing.
Two of the four blast devices were attached to bicycles and hence police are questioning cycle shop owners in the city.
"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.
Home Minister R.R. Patil, who visited the blasts sites early Thursday, said it would be "premature" to term them as an act of terror.
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 Feb 13, 2010, a major explosion had ripped through the German Bakery in the city's posh Koregaon Park, killing 17 people, including some foreign nationals, and injuring 64 others.