Pune blasts: Old ammonium nitrate may have reduced intensity

“This makes the blast cause an impact in a specific direction. Ball bearings were placed to cause injuries. But the circuit has only caused the detonators to explode and so all the main charges at all the places have not exploded,” said an expert from the CRPF’s Institute of IED Management in Talegaon which investigators consulted.

The damage,however,was largely contained as the ammonium nitrate is suspected to have been from old stock. Commercial ammonium nitrate has a shelf-life of three months and is further known to lose its capabilities in humid weather,other forensic experts said.

The bombs were unique in their use of three detonators — similar bombs used in the past depended on two. “The circuit shows an expert mind as two power supplies have been used. This was to ensure that if one source of energy falters,a standby source can be used,” said an officer. “But so far,terror groups have not gone beyond using two detonators. This one had three.”

The three detonators did not explode in none of the four blasts,investigators are questioning why the detonators were connected “in series” to power sources— another cause that may have contributed to the ammonium nitrate just burning and not exploding.

“The question now is,with a well-crafted IED,why will connection to the power supply be wrong? Why will bad quality explosives be used? Was this deliberate or was it a fault? These are leads we are chasing,” an officer said.

The expert from the IED Management Institute said,“It has been observed such explosions are done with a motive to experiment with IEDs. It could also have been done to send a message to the government. None of these possibilities can be ruled out.”