PUNE/NEW DELHI: Less than 24 hours after minor blasts rocked Pune, security experts on Thursday were stunned by evidence that the serial explosions were part of a full-blown terror attack, which providentially went awry, preventing mass casualties on the city’s bustling Jangli Maharaj road.

An official said a design flaw in the bombs caused them to explode partially and prevented the shrapnel from spreading.

Without naming any group, a top home ministry official in New Delhi said there were “credible leads” pointing to a “big plan” by a terror outfit. “Preliminary forensic result which is an outcome of the detailed examination of the two unexploded IEDs and nature of blasts shows that the bomb had all the ingredients to cause a much bigger impact and had the potential to take lives of many people.”

In Pune, police bomb experts who supervised dismantling of the devices also said the four bombs placed on Jangli Maharaj road on Wednesday evening exploded only partly. Had these and the two that were defused gone off fully, the damage caused would have been “major”, they said.

A bomb disposal officer, speaking on condition of anonymity, told TOI each bomb contained two or three detonators, a nine-volt battery, a circuit, a timer, ball bearings and a yellow sticky substance. “The design of the bombs was faulty, due to which they did not explode fully. The bearings were by and large intact even in the devices that went off. Had the bombs exploded fully, the bearings could have injured several people,” he said.

The officer said at least five detonators did not explode. “We defused these detonators at our office at Shivajinagar,” he said. The expert said a sticky substance covered the detonators, batteries and bearings in each bomb. “We have sent the substance to the state forensic laboratory for chemical analysis,” he said. Police were probing whether the bombs contained ammonium nitrate, a powerful explosive. On Wednesday, police had said there were four blasts and one device had been defused before the timer could go off.

Sources in New Delhi, meanwhile, said the manner in which digital wristwatches were used as timers and the detonator circuits along with the way bombs were kept on three newly-bought bicycles, one dustbin and two polythene bags were similar to the technique adopted by the banned terror group Indian Mujahideen. The terror outfit had adopted a similar modus operandi in the serial blasts in Lucknow, Faizabad and Varanasi in November, 2007 and in Jaipur in May, 2008.

Union home minister Sushilkumar Shinde and home secretary R K Singh, however, remained reticent about the horrific revelations. “We have taken it very seriously,” said Shinde, indicating that the low-intensity blasts were not being dismissed as a mere messaging by a terror group and the government was aware of a carefully-scripted plan.

“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,” said home secretary R K Singh.

Meanwhile, Pune police on Thursday identified the shop from where two of the three new bicycles were purchased by the terrorists. Officers said two men bought the bicycles from Soni Cycle Trading Company at Phadke Haud, Budhwar Peth, around 11am on Wednesday, about eight hours before the first bomb went off. The police have questioned the owner of the shop, his brother and two employees and based on descriptions given by them, sketches of the two men have been prepared.

The shop owner also told police the two men were speaking Gujarati. A senior police officer from the crime branch told TOI that the shop was traced with the help of serial numbers embossed on the bicycles. “We searched several bicycle shops in the Phadke Haud area,” an officer said.

The officer said police have also taken CCTV footage from a firecracker shop in Shaniwar Peth. “The shop owner has installed a high-resolution camera at his shop. The camera is facing the road. We are suspecting that the duo may have used the road in front of the shop.”

Meanwhile, police are still questioning Dayanand Patil, the man injured in first of the blasts at Balgandharva chowk. Cops also questioned his wife, Satyakala, in Pune and recorded her statement. Police said Patil had visited either Jordan or Dubai in 2003. They have seized his passport and are trying to ascertain the reason for his visit abroad. Police refused to say whether he was being seen as a suspect in the blasts. Patil works as a tailor at a laundry on Shirole road, a few metres from Balgandharva chowk. He lives in Urulikanchan, 20 km from the city, with his wife and three-year-old daughter.