Investigators probing the blast near the Red Fort have compiled a detailed log of every vehicle that entered the adjacent parking area where the exploded car remained for three hours, an official said on Saturday.

They are tracing registration numbers and questioning drivers and owners to determine whether anyone noticed the Haryana-registered Hyundai i20 that later detonated.

The Delhi Police Special Cell has also registered a separate FIR under criminal conspiracy sections to investigate any wider plot behind the explosion. The earlier FIR filed under the Unlawful Activities (Prevention) Act has been transferred to the National Investigation Agency.

According to sources, several vehicles were parked in the vicinity on Monday when Dr Umar Nabi, who was driving the car that blew up, left it in the lot.

"Every driver who was present there around that time is being traced to determine whether they saw the HR-26 car, how many people were inside it, and whether anyone else was accompanying Umar," a source said.

Investigators are showing drivers Umar’s photograph to verify whether he was alone or if anyone entered or exited the vehicle during the three-hour period it was parked, an official said.

The aim is to reconstruct the exact chain of events and establish whether the explosive device was planted during that window.

Parallel enquiries are examining whether the arrested doctor, Dr Muzammil Ganaie, was in frequent contact with a group of doctors associated with Al Falah University in Haryana’s Faridabad district.

Sources said around 15 doctors linked to the university and known to be in touch with Muzammil are currently untraceable.

"Call detail records showed multiple conversations between Dr Muzammil and several doctors. When the agencies attempted to contact them, their phones were found switched off. A team sent to Al Falah University for questioning discovered most of them missing," a source said.

Investigators are now trying to determine whether the missing individuals had any role in planning or facilitating the suspected terror operation.

On November 10, agencies unearthed what they described as a "white collar terror module" operating across Jammu and Kashmir, Haryana and Uttar Pradesh; seized 2,900 kilograms of explosives; and arrested eight people, including three doctors. Just hours later, a high-intensity blast tore through a slow-moving car near the Red Fort metro station, killing 13 people and injuring several others.