New Delhi, Nov. 13 -- Two days after a blast ripped through the heart of Old Delhi, killing at least 10 people and injuring dozens, investigators are piecing together the puzzle of what happened - and why. The Hyundai i20 that exploded near the Red Fort on Monday evening has given rise to four key questions that now dominate the probe: why that location, whether the blast was planned or accidental, if the bomb was hidden in the car's bonnet, and who was in the car. Perhaps the most pressing question is why the attacker chose the busy intersection outside Red Fort - one of the most tightly policed areas in Delhi. National Investigation Agency officials are examining whether the explosion, which occurred at 6.52pm amid evening rush-hour traffic, was accidental, premature, and triggered in panic. Delhi Police officers familiar with the probe, speaking on condition of anonymity, said they have reasons to believe that Dr Umar un-Nabi - the chief suspect had in fact planned the blast around the Mughal-era heritage structure and Chandi Chowk, which is always packed with shoppers. CCTV footage shows the white i20 in and around the area for nearly four hours - parked for more than three hours near Sunehri Masjid and later moving along Netaji Subhash Marg and Shantivan Road between Daryaganj and the Chhata Rail Cut traffic signal. The car even halted briefly near a temple on Netaji Subhash Marg about 10 minutes before the explosion. "We are not ruling out the possibility that the suspect, who was driving the car, may have attempted to trigger the blast around the temple first," the officer cited above said. The next question troubling investigators is whether the explosion was the result of a deliberate plan or a desperate act. "We are examining why the suspect chose Monday for a blast at Red Fort since the monument is shut on Monday. We are probing if the multiple arrests of his associates across states led to panic," said second police officer. Equally puzzling, investigators said, is how the device was assembled and where it was placed. A senior police officer said that Umar's car appeared normal in CCTV footage from Faridabad on Sunday night, but when it was seen at the Sunehri Masjid parking lot in the afternoon, hours before the explosion, the bonnet appeared only partially shut. "We have reason to believe that Umar hid the detonator and possibly ammonium nitrate fuel oil (ANFO) inside the car's bonnet. Our suspicions were confirmed when we found the gap and that he used a rope and sticker like object to close the bonnet. In CCTV footage from Sunday night, there was no rope or object there," a senior police officer told HT. The second officer cited above said the forensic team later confirmed that the car's bonnet area showed high traces of ammonium nitrate. The latest evidence points to Umar being the sole occupant during the explosion. Investigators said they are trying to identify those two men and determine whether they had any role in assembling the device or aiding Umar's escape. One officer from the Delhi Police's Special Cell said, "We have some leads on the identities of the two men."...