Investigation
According to the Hindu, two men on a motorcycle wearing black shirts, jeans and helmets planted the bomb. Investigating authorities revealed that ammonium nitrate, sulphur and potassium were used to cause the low-intensity blast.
A team of National Security Guards was deployed to assist the investigating authorities. Delhi Police had detained five persons at the Indira Gandhi International Airport whom they suspected of having a role in the blast. According to Hindustan Times, the police also selected several Bangladeshis for interrogation. NDTV said that there was a possibility that the attack was not carried out by the Indian Mujahideen, which claimed responsibility for the serial attacks in Delhi two weeks before, since the bomb which went off in Mehrauli was quite different.
Police in Faridabad had identified and held the man who sold the sim card to the terrorists from which the attackers had made a call to media agencies threatening another terror strike moments before the blast. The police also detained the person whose cell phone was used to make the call. The police across NCR had increased patrolling at various access points.
The Deputy Commissioner of Police for Delhi, Alok Kumar, said, "The evidence collected so far indicates that the bomb had no timer or detonator and it was low-intensity. We do not think it was linked to the Indian Mujahideen or any other terror group. In the recent past, in the stretch between the IP flyover and the Andheria road-junction in Mehrauli, there have been instances when bike-borne youths have dropped bombs in crowded streets." The Indian Express revealed that the bomb was quite similar to those made by Abdul Karim Tunda, an alleged terrorist who has been linked to several prior terrorist attacks in India.
The police also reported that they had received a call before the blasts saying, "Save Delhi, there will be blast!"
Unlike the Mehrauli and Malegaon blasts investigations, police in Delhi have ruled out Hindu groups as having perpetrated the blasts, a move drawing increasing polarisation as a result of the aforementioned investigation. The groups had been "under the scanner." The police cited their ruling out of the Hindu groups as the "signature (type) of the explosive used in Mehrauli was different from those used in Modasa and Malegaon." He did add that while "Low-intensity explosives were used in three places... they were not identical. The timer mechanism used in Mehrauli was different from the one used in Malegaon/Modasa that indicates the former was the handiwork of a separate outfit. In Mehrauli, the bomb was timed by its acidic contents, while in Malegaon/Modasa the bomb was set off by a timer based on the batteries of the bikes used to plant them."
Read more about this topic: 27 September 2008 Delhi Blast