More than 2 kg of ammonium nitrate was used in the deadly blast near Red Fort in Delhi this week, sources linked to investigating agencies said on Saturday.
Umar Nabi, the driver of the car that exploded on November 10, killing 13 people, was an "expert" in making bombs, sources said.
More than 52 explosive samples obtained by the forensic team so far reveal that Umar may have prepared the explosive using ammonium nitrate, petroleum, and detonating material, according to sources.
Forensic investigations have also revealed that such explosives can be prepared in about 5 to 10 minutes. The security agencies are also probing if Umar Nabi prepared the explosives at the nearby parking lot, where he had parked the car for over three hours before the explosion.
He entered the parking lot at 3.19 pm and exited at 6.28 pm, about thirty minutes before his Hyundai i20 stopped at a traffic signal near the Red Fort Metro Station and exploded, killing thirteen people, injuring over 20 others, and damaging several other vehicles in the congested area.
Sources said that Umar, a Kashmiri doctor affiliated with the Al Falah University in Haryana's Faridabad, initially planned to detonate the bomb near the parking at Red Fort, a tourist area that also houses a busy market. But he reportedly "panicked" after the arrest of his associates and the massive recovery of explosives in Faridabad and missed that Red Fort, popularly known as Lal Qila, remains shut on Mondays. When he reached the parking lot, he saw that there was no crowd.
After a three-hour wait, he drove out onto Netaji Subhash Marg, which runs along the Red Fort on one side and Chandni Chowk on the other, and exploded the car at the traffic signal.
Nabi had panicked after his two aides, Muzammil Ahmad Ganaie and Shaheen Saeed, who also worked as doctors at the Al Falah University, were arrested in connection with the wider probe into a 'white collar' terror module.
Hours before the Red Fort blast, Jammu and Kashmir Police had announced that it had cracked an inter-state and transnational "white collar" terror module, linked to the Pakistan-based Jaish-e-Mohammed and the Ansar Ghazwat-ul-Hind, an al-Qaeda-affiliated terror group.
It said it also seized 2,900 kilograms of explosive substances and arrested seven people.
Track Latest News Live on NDTV.com and get news updates from India and around the world