"I think in the next couple of days, all the key persons who have to be questioned by us will be quizzed. We would like to complete it soon. I think the SIT will soon do it," he told reporters here on Friday outside Police Headquarters when asked when would Tharoor be questioned in the case.
He also denied reports that the viscera samples which are almost one-year-old must have been spoilt by now and would not reveal the kind of poison that caused Sunanda's death even if it is sent abroad.
"The samples are kept with preservatives, they have a shelf life. Unless there are some issues with the way they have been kept or the way they were preserved during sampling they will not get spoilt," he said.
Bassi had yesterday said that a definitive decision over where the viscera will be sent will be taken in the next couple of days. Police may send the exhibits to labs in US or UK.
The police chief refused to reveal what the SIT has come across so far during questioning of several individuals so far.
"Whenever there is a questioning we always get to know certain things. All these things will be taken into cognizance and a conclusion will be drawn," he said.
51-year-old Sunanda was found dead in her suite at a five-star hotel in south Delhi on the night of January 17, 2014, a day after she was involved in a spat with Pakistani journalist Mehr Tarar on micro-blogging website twitter.com over the latter's alleged affair with Tharoor.
Delhi Police had registered an FIR in this connection on January 1 and an SIT has been formed to investigate the case.