In a latest development in Sunanda Pushkar death probe, sources have said that the Special Investigation Team (SIT) has carried out polygraph test on three key witnesses. A Delhi court last month had permitted the police to conduct the lie detector test on three witnesses- former Union minister Shashi Tharoor's domestic help Narain Singh, Tharoor's driver Bajrangi and his family friend Sanjay Dewan, after the three had said that they had no objection if the polygraph test was conducted on them. Sunanda was found dead in the 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. Investigators are waiting a report from Federal Bureau of Investigation to know about the kind of poison found in Sunanda's body. Sunanda's viscera samples were sent to the FBI lab in Washington in February to determine the type of poison that is suspected to have caused her death. An AIIMS medical board had identified poisoning as the reason behind her death but did not mention the type of the poison. Sunanda was found dead in a five-star hotel suite in Delhi 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.