The bombs that wreaked havoc in Mumbai the previous night may have been a deadly mix of ammonium nitrate, explosive TNT, oil and ball bearings preliminary investigations revealed on Thursday.
According to sources, investigators are also in possession of the crucial footage recorded by CCTV cameras installed at Opera House and Dadar - the third blast site was Zaveri Bazar. The CCTV cameras hold the key to the probe and may help in identifying those who planted the explosive devices.
The sources said forensic experts had collected traces of ammonium nitrate, fuel, TNT and ball bearings from the blast sites which may lead to the perpetrator of the terror attack that killed 17 and injured 131.
It is the worst terror attack in India after the November 2008 strike that left 166 Indians and foreigners dead.
They said that evidence from the sites suggested that battery power was used to trigger the blasts for which at least seven improvised explosive devices (IEDs) have been used.
Ammonium nitrate, a chemical compound that enhances the combustibility of explosive devices has been a favourite of terrorists. The chemical is used in an agricultural fertiliser.
Mixed with fuel, like diesel, petrol or kerosene, and powered with booster charge and detonator, the cocktail turns into a bulk explosive. Pieces of metals, which can be nails or ball bearings, are added for shrapnel effect.
When the device is detonated, the metal pieces act like missiles.
Home Secretary R.K. Singh told reporters in Delhi that the IEDs used in the blasts were "not crude" and indicated that they were prepared with "some level of sophistication".
Though the ammonium nitrate used in the explosions has been confirmed by officials, investigators said they faced difficulty in ascertaining the exact composition as rains had washed away the evidence.
Rakesh Maria, the chief of Maharashtra's Anti-Terrorism Squad (ATS), said in Mumbai that ammonium nitrate was used in the explosions but to know the real composition of the bombs would take “little longer”.
He said “prima facie it appears a timer device” was used to trigger the blasts but refused to say it with certainty.
Home ministry officials in New Delhi said an electric circuit was recovered from a dead person's body.
“But it cannot be said for sure that the person was a suicide bomber. He may have been very close to the bomb,” Secretary for Internal Security U.K. Bansal told reporters.
The key to the identification of bomb planters remains in the “voluminous” CCTV footage collected from the blast sites.
However, even this is proving to be a little difficult. The sources said the ATS was trying to retrieve the footages recorded by not so high resolution cameras.
The visuals need some cleaning because the footage is fuzzy due rains and bad light on Wednesday evening when the blasts were triggered.