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 car that exploded near the Red Fort on Monday evening has given rise to four key questions that now dominate the investigation: why that location, whether the blast was planned or accidental, if the bomb was hidden in the car's bonnet, and who exactly was inside the vehicle. 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 (NIA) 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 investigation, speaking on condition of anonymity, said they have reasons to believe that Dr Umar un-Nabi - the chief suspect, who investigators believe was likely driving the car - 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 famous 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, as the area around it and another religious structure facing the main road, is a gateway to multiple wholesale markets in Chandi Chowk," the officer cited above said. "There is also a possibility that Umar halted the vehicle near the temple but had to move ahead as it's a no-parking zone, and his halt might have drawn the attention of security and traffic personnel. He likely panicked and moved ahead," the officer said. The next question troubling investigators is whether the explosion was the result of a deliberate plan or a desperate act. Officers are examining all three possibilities - a premeditated attack, a panic-induced detonation, or an accidental blast caused by an unstable device. "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 which resulted in Umar fleeing with the explosive. The improvised plan may never be known as the one who decided and executed was among the people killed in the explosion," said a second senior police officer aware of the probe. Equally puzzling, investigators said, is how the device was assembled and where it was placed. Early forensic analysis appears to suggest that the bomb was likely hidden under the car's bonnet, one of the officers cited above said. 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. "This indicates the explosive's source was concentrated there," said another investigator. While initial reports and investigation suggested that two people were inside the vehicle, the latest evidence points to Umar being the sole occupant during the explosion. "When the car entered Delhi from Faridabad on Sunday night, he was alone," an officer said. "He was seen with two persons on October 29 at a pollution checking station in sector 37 Faridabad. After this, he went hiding for 10 days," said an officer. Investigators said they are now 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 and are verifying their movements."...