13/7 clues: Two phones,J&K-type timer chip,shreds of gunny bags

The three bombs used a mix of ammonium nitrate and fuel oil and were triggered by a timer device,most probably alarm clocks although NSG experts involved in the probe think it could have been a mobile phone alarm. They are also believed to have recovered two suspect phones from the blast sites,sources told The Sunday Express.

Investigators now suspect that the bombs were transported and kept in white gunny bags made of PVC. Besides the timers,tiny metal pieces and explosives,the only other common element found at the three locations in Zaveri Bazaar,Opera House and Dadar Kabutarkhana are small pieces of gunny bags. This information is being used to hunt for suspects who may be seen carrying such a bag in the CCTV footage from the blast sites,the sources said.

While investigators continue to suspect the Indian Mujahideen,forensic experts have found only one strong similarity between the three blasts and earlier blasts across the country blamed on IM.

The bombs were kept at a similar height in the serial blasts in Hyderabad in 2007 which targeted Gokul Chat Centre,Lumbini Park and Dilshak Nagar bus stop. The plan,arrested IM members are believed to have said,was to make maximum impact by causing head injuries and killing more people,sources said. A similar method was followed in Surat in 2008.

On the other hand,the three bombs had some similarities to the bombs that targeted local trains in Mumbai in July 2006. Both sets of bombs did not contain projectiles like ball bearings or nails used in IM bombs. Instead,both sets of bombs are suspected to have been placed inside metal containers and close to larger metallic bodies which splinter and kill.

While the Dadar bomb was placed on a metal-framed bus shelter,the Opera House bomb was placed very close to a scrap vendor and at Zaveri Bazaar it was on the foot-rest of a scooter.

Boosting this theory is also the similarity in the sizes of the holes caused by the two sets of blasts and the fact that both bombs contained a nitro compound,sources said. The 2006 attack was blamed on the Lashkar-e-Toiba and the SIMI.

One new element discovered in one of the three Mumbai bombs is the presence of a timer chip called Silicon Control Rectifier (SCR). This chip was found on top of an advertising hoarding 40 feet from the ground,opposite the blast site in Dadar. Sources said such SCRs have been used in the bombings in Bali,in the Philippines and by insurgent groups in Thailand.

In India,SCRs were found in bombs placed by militants in Kashmir and defused by security agencies. SCRs,sources said,are used in cellphone chargers and laptop adapters,among others.