"From the circumstantial evidence collected so far and from the statement of witnesses, there is no reason for us to proceed in any other fashion so we are carrying on our inquiries under Section 174 CrPC," the police commissioner told reporters here.
Inquest proceedings under Section 174 CrPC were initiated in the Sunanda case according to which a Sub-divisional Magistrate inquires into the death of a woman if she dies within seven years of her marriage.
In this case, on January 21, a sub-divisional magistrate had directed Delhi Police to investigate the murder or suicide angle in the case after autopsy report has cited the death as "sudden and unnatural" while the cause of death was mentioned as poisoning.
The police can file an FIR in this case if it finds any foul play but until then the inquiry will go on under section 174 CrPC.
Investigators were banking on the viscera report from CFSL to get definitive lead on the nature of the poison and establishing its quantity but the report has failed to do so. The viscera report hints toward drug poisoning and its findings are still inconclusive to file an FIR in the case, according to police.
"The CFSL report has not been able to give much headway into the probe. It rules out poisoning and hints toward drug poisoning," said a senior police official associated with the probe.
Investigators will now take the opinion from the panel of doctors from AIIMS which had carried out an autopsy to shed light into findings of the Central Forensic Science Laboratory (CFSL) report.
The SDM has also been informed about the CFSL report.
Sunanda, 52, was found dead in a 5-star hotel in South Delhi on the night of January 17, a day after her twitter spat with Pakistani journalist Mehr Tarar over an alleged affair with Tharoor.
In a report to the police, the SDM, who had recorded the statements of Sunanda's brother, son, Tharoor and his staff, had said that no family member suspected any foul play in the death.
The autopsy report had mentioned more than a dozen injury marks on Sunanda's both hands and an abrasion on her cheek which suggests a "use of blunt force", besides a "deep teeth bite" on the edge of her left palm. Viscera samples were preserved after the autopsy at AIIMS and were sent to CFSL for further tests.
The search and seizure memorandum of the police, which is a part of the report, mentioned finding of mix of two drugs - Alprazolam and Excedrin. Excedrin is a combination of acetaminophen, aspirin, and caffeine while Alprazolam is an anxiolytic.
The probe into the case was handed over to the Crime Branch on January 23. However, the case was transferred back to the South District police two days later on January 25.