Sunanda Pushkar was found dead in a five- star hotel in South Delhi on the night of January 17, 2014.
Shashi Tharoor's wife Sunanda Pushkar, who committed suicide in 2014, have been brought back from the US by the members of a Delhi Police team probing the high-profile case.
The samples lying with a FBI lab in the US for over a year were brought back by DCP (south) and investigating officer of the case in the on Tuesday evening, said a senior Delhi Police officer.
The samples are court property and the team was sent to bring them back.
The FBI lab has already given its report on the samples, said the officer.
The samples were sent to the FBI lab in Washington in February 2015 to determine the kind of poison that killed Sunanda after an AIIMS medical board identified poisoning as the reason behind her death but did not mention any specific substance.
Delhi Police had in January 2015 registered a case of murder in connection with Sunanda's death.
The FBI report sent to Delhi Police in November 2015 had virtually ruled out the theory of 'polonium poisoning' having caused her death. However, after Delhi Police failed to draw any conclusion on basis of the findings, the report was handed over to a medical board for examination before further proceedings in the high-profile case.
The medical board is yet to give its opinion on cause of Sunanda's death. They had demanded for some papers and clarifications which were provided to them, said a senior officer privy to the probe.
"The next line of investigation will be decided after the board comes out with its report," added the officer.
51-year-old Sunanda was found dead at a suite in a five- star hotel in South Delhi on the night of January 17, 2014, a day after her spat with Pakistani journalist Mehr Tarar on Twitter over her alleged affair with Mr Tharoor.
Several persons including Mr Tharoor have been questioned in connection with Sunanda's death. The police have also conducted polygraph test on six persons, all prime witnesses in the case, including Mr Tharoor's domestic help Narayan Singh, driver Bajrangi and Sanjay Dewan, a close friend of the couple.
In February, Ms Tarar was questioned about her relation with the Congress leader and his wife, her fight with Sunanda over Twitter, and other issues revolving around Sunanda's death.