Sources in Delhi police said court's permission to conduct a polygraph test on Tharoor was likely to be sought soon as the investigators were trying to take the high-profile case to a logical conclusion.
The investigators have so far conducted polygraph test on six persons, all prime witnesses in the case, including Tharoors' domestic help Narayan Singh, driver Bajrangi and Sanjay Dewan, a close friend of the couple.
Tharoor was not subjected to the test but was questioned thrice in the case. 52-year-old Sunanda was found dead in a five-star hotel suite on January 17 last year, a day after she was involved in a spat with Pakistani journalist Mehr Tarar on Twitter over the latter's alleged affair with Tharoor.
The sources said Tharoor is likely to be questioned again as the eight-page FBI report of Sunanda's viscera broght to fore certain details crucial to the probe. The police will soon submit the report to court.
The report received via e-mail on Tuesday, suggested that Sunanda died of some poison, which they have named, said sources. However, police have so far refused to disclose the type of poison mentioned in the report.
Delhi Police Commissioner B S Bassi said the report from the Washington DC-based laboratory of FBI would soon be handed over to a medical board for examination.
"The FBI lab had conducted analysis of various substances. And this should give an indication (as to the reason behind her death) once the doctors go through the report," said Bassi.
The report has ruled out the theory of the variant of a radioactive element named Polonium having caused Sunanda's death, Bassi said, adding that radiation levels in her viscera samples were "within the standard safety norms".
Analysis of the report shall take time and, even after submission in court, it shall only be shared once all the legal issues connected with it have been studied, he said.
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