Delhi Police Commissioner B S Bassi said that the final medical report from AIIMS has revealed that Sunanda, wife of Congress MP Shashi Tharoor, died of poisoning but it was not clear whether it was injected or administered orally.
The report also did not mention the kind or nature of the poison while mentioning a list of possible chemicals which could not be detected in Indian labs.
Police has registered a case of murder against unknown persons in the case.
Sources said Polonium 210, a radioactive isotope is suspected to be the poison that may have caused her death.
"The viscera samples may now be sent to an FBI lab in the US or lab in UK," said a senior police official.
Earlier medical reports had mentioned 12 injury marks on Sunanda's body including an injection mark on her hand and a teeth bite.
Doctors from the medical board had visited the crime spot (suite of the five-star hotel) in the first week of November along with police officials where they examined the room and lifted samples.
After analysing it, they have submitted the third and final report in the case on December 29.
"The medical board had maintained that the death was unnatural and due to poisoning. However, it has clearly listed a number of poisons, most of which are radioactive chemicals which cannot be detected during forensic tests in Indian labs including thallium, polonium 210, nerium oleander, snake venom, photolabile poisons and heroin," the sources said.
A Special Team which has been formed to probe the case will investigate the case from scratch.
The team is likely to question Tharoor, his relatives and personal staff along with the employees of the five-star hotel where she was found dead on January 17 last year, the sources said.
It will also examine the hotel doctor who declared Sunanda dead and go through CCTV footage of the hotel. The forensic report of Sunanda's mobile phones and laptop which were sent for tests will also be evaluated.
The AIIMS medical board had, in its second report submitted to police on September 30 last year had also confirmed poisoning as the reason for her death but did not mention the type of poison.
The 12-page "Subsequent Medical Board Opinion" said her brain, kidney, lungs and liver were functioning normally and that her death was caused by poisoning.
The viscera report of CFSL in March last year had hinted at drug poisoning but police considered it as inconclusive. Police then asked AIIMS to re-examine the report and give its findings.
Sunanda 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.
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.
In its report AIIMS medical board had said, "The cause of death in this case is poisoning. Viscera are positive for ethyl alcohol, caffeine, acetaminophen and cotinine."
From the medical document made available to them the panel has also concluded that Sunanda did not have cardiac problem. She was not suffering from any diseases like hypertension, diabetes or tuberculosis.
The panel has concluded that Sunanda was neither ill nor had any disease prior to her death. She was a normal healthy individual.
The medical board had examined all the injuries on her body out of which 'injury number 10' has been termed as a mark caused by the needle of a syringe.
The team has also dismissed the theory that Sunanda died of an overdose of Alprazolam as the viscera report is negative for the presence of the substance.
"None of the treatment documents of Sunanda Pushkar has mentioned prescription of Tablet Alprax which was found at the scene of death. Two used Alprax strips of capacity 15 tablets each were recovered from the spot. However viscera report is negative for presence of Alprazolam," the report said.
The panel also suggested that police investigate a few things.
"There were medicines recovered from scene of incident - hotel room - in which the deceased was found dead. Who prescribed these drugs, from where these drugs were procured and for whom these drugs were prescribed?
"Exhibit number 2, having one wet purple colour top of make 'Relax, rest Sleep' having very faint off- white stains at six places and one wet purple colour printed lower of make "M & S", is positive for acetaminophen, caffeine, lidocaine and Methylparaben - it is a circumstantial evidence and requires further investigation," the report said.
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