In the past, the timer devices used in bombs have given clues on the groups involved. In August 2007 twin blasts in Hyderabad, a failed bomb under a pedestrian overbridge in Dilsukhnagar had given key leads to investigators.
A wrong placement of batteries was found to be the reason for the failure of the device. When taken apart a quartz timer of Samay make was found. The same timer or a variant with the brand name Prince were used in terror attacks at Jaipur, Ahmedabad, New Delhi through 2008 and Bangalore in 2010.
The Indian Mujahideen, suspected to behind the latest blasts, is known to prefer timer of Samay make.
Hindu right wing groups linked to Mecca Masjid, Ajmer and a Hubli court room blasts used cellphone alarms as timers.
We have not found pieces of any timer device. There were claims but there is nothing on the evidence table. Our broad guess is that a quartz timer of some sort was used, sources said.
IM men like Arif Badruddin Sheikh arrested by the Mumbai crime branch in late 2008 had told interrogators that the group had at one time experimented with Ajanta brand of clock but found that the IEDs did not work to expectations.
Sources say IM members bought 50 Samay clocks ahead of the Ahmedabad blasts of July 26, 2008, where 21 bombs were triggered in the span of 70 minutes.
In the blasts at the Chinnaswamy Stadium on April 17, 2010, one of the main investigation trails was the Samay clocks in the failed bombs. Investigators tried to compare the serial numbers of the clocks found on the failed bombs with those found at other sites but made little headway.
While the presence of quartz timers have come to be viewed as Indian Mujahideen signatures, the outfit has in recent times experimented with microchip timers and digital wrist watch timers too.
Despite the presence of leads in the August 2007 twin blasts in Hyderabad from an unexploded device it was the chance arrest of a group of Indian Mujahideen operatives by the Mumbai crime branch in September 2008 that finally helped crack the case.