Husband Shashi Tharoor, son Shiv Menon, friends & family gather around the body of Sunanda Pushkar, who was found dead in the Leela Palace hotel, at a crematorium in New Delhi on January 18. Husband Shashi Tharoor, son Shiv Menon, friends & family gather around the body of Sunanda Pushkar, who was found dead in the Leela Palace hotel, at a crematorium in New Delhi on January 18.

Doctors of the All India Institute of Medical Sciences (AIIMS) on Tuesday said that it would not be easy to find out the absolute cause of Sunanda Pushkar's death. The AIIMS doctors, who conducted the autopsy of former Union minister Shashi Tharoor's wife, however, maintained that she had died of poisoning.

"Our duty was to give an opinion to the police, and we have already done it. Whatever I had said earlier were my findings, not my stand. Our report doesn't mention death is homicidal in nature. It is due to poisoning. Now it is for the police to probe further," said Dr. Sudhir Gupta, one of the doctors in the forensic science department of AIIMS, who conducted Sunanda's post-mortem.

Asked whether it is a murder or suicide, Gupta said it was the job of the police to find out. Gupta had earlier alleged that two former Cabinet ministers pressured him to show Sunanda's death as natural. On Tuesday, however, he chose to keep quiet. Doctors at the premier institute said it would take some more time to conclude the case. Read: Sunanda Pushkar death: Stunned it's now a murder case, says Shashi Tharoor

Leela Palace hotel where Sunanda Pushkar was found dead Leela Palace hotel where Sunanda Pushkar was found dead This is a sensitive and highprofile case. The murderer (if proved) would have planned it in a smart way so that it would be tough to identify the exact poison. She couldn't have been killed with any normal poison. There have been several cases in which the exact poison, used to kill somebody, was identified even 10 years after the crime was committed," said a doctor who was part of the medical panel that examined Sunanda's case.

"So far, we have given three reports to the police. The police have shown a lax attitude towards the case. It will be very difficult to find out the poison because there are several limitations and restrictions in laboratory facilities in India. By the time the police take a stance on taking the viscera samples to some other country for investigation, the intensity of certain poisons may also diminish with time. That is why it is always said that such cases should be investigated as soon as possible," the doctor said.

Doctors have said the samples would require "quantitative estimation". In India, quantitative estimation is done only for alcohol.

"Homicidal poisoning is a rare entity. The murderer would have certainly chosen a different idea to kill her. This matter still needs meticulous investigation. When we visited the crime scene last time, we found some urine spots on the bed cover and sent them for investigation. Even the urine sample showed poison, which proved that it was metabolised through her body," the doctor said.

"The police will need to find a motive and then catch the murderer. Some medicines were also found from the crime scene. Interestingly, any medicine can prove fatal, if consumed in high quantities," he said. Delhi Police Commissioner B. S. Bassi said the Delhi Police, which is investigating the case, would have to send the samples abroad (see accompanying story) since the quantification of poisons could not be done in India.

"In order to do so, the Delhi Police had to register a case; thereby we have done the needful. We have registered a First Information Report (FIR) under Section 302 of the Indian Penal Code," Bassi added.