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The forensics team analysing samples collected from the three blast sites in Mumbai is struggling to decipher the exact make of the timer device or the trigger used by the bombers to detonate the explosion.
While provisional forensic reports have clearly established the use of ammonium nitrate as the explosive, it's the determination of the detonator or the timer device that's proving to be a challenge for the forensic officials. "Most of the time remnants of the timer device are recovered from the blast site, but if the temperature is too high then it's possible that the timer device may have been destroyed," said Dr Rukmani Krishnamurthy, former director of the Forensic Science Laboratory of Maharashtra. The other possibility is that the timer device was destroyed either in the rains during the blasts or the chaos that followed at the site of the blasts.
The forensic report also pegs the weight of each bomb to be anything between four and six kg. In addition to ball bearings, forensic experts have collected one inch long cylindrical sharpened iron rods or shrapnel from the blast sites. All metal used is approximately one inch thick. Traces of ammonium nitrate / fuel oil have also been conclusively established.
Even before the forensic reports were ready, it was the witness statements recorded immediately after the explosions that gave investigators their first initial confirmation on the usage of ammonium nitrate in the blasts. Most of the witnesses informed the police that they saw white gas emitting from the area of explosion, symptom of ammonium nitrate combustion. Also, the National Security Guard's vapour detectors helped them get initial confirmation of the use of ammonium nitrate in the blasts.
Forensic experts working on the investigations feel that given the precision of the time between the three blasts, one thing is clear, that a digital timer device was used. But efforts are still underway to conclusively figure out the exact nature of the timer device. In most cases the timing mechanism is an improvised ordinary household object such as a wind-up alarm clock, wrist watch, a mobile phone etc. A timer device can be chemical, mechanical, digital or even analog in nature.
Identifying the timer device is crucial as it will help the investigators to match the mechanism with the pervious records of the blasts where timers have been used. In the past, terrorists have used timer devices to trigger dozens of blasts across India including 7/11 in Mumbai, the Ahmedabad serial blasts, and as recently as the low intensity blast at the Delhi high court in May this year.
Further analysis suggests that the bomb at Dadar's Kabutarkhana seems to have been thrown in haste inside the electric box of the bus stand panel. The haphazard position of the blast considerably contained the impact of the explosion, restricting it to 60 degrees as against the expected 180 degrees impact. Due to the height, the majority of the impact was absorbed by a tree and a car that was parked near the bus stop, resulting in minimum number of injuries and zero casualty.
At Zaveri Bazaar, initial assessments suggest that the explosive was placed inside a scooter in an improper position. The bomb had a high quantity of ammonium nitrate. Due to the presence of adjoining scooters, the explosion resulted in leakage of petrol which in turn led to fire in the area. However, an even massive disaster was averted because the scooter was parked under an open sky. And because the explosive was kept in an improper position, the direction of the blast was toward the open space.
At Opera House, too, the bomb was kept in a ditch at a 60-degree angle. Primary reports suggest that had the angle been 30 degrees, far more people would have been injured.
As of today a total of 19 deaths and over 134 injuries have been confirmed. However, after the immediate assessment of the blast sites, officials feared the number could have been much higher. According Dr Rukmani Krishnamurthy, ammonium nitrate, a high intensity explosive, coupled with the population density in the area, could have been far more disastrous. "More importantly, there are a number of factors that come into play to create damage."
The direction of wind, velocity of the secondary missiles (metals in the surrounding area that get blown away), quantity of explosive, quantity of the primary missile (eg, iron filing, ball bearings etc), containers, placement or the position of the bombs, obstructions during the explosion, time of the day, etc all determine the intensity of the explosion and the damage it can cause.