Sources say doctors found traces of Alprazolam, an anti-depressant, which indicates that Sunanda Pushkar Tharoor died of an overdose of some strong medicine or sedative. There was no trace of alcohol in her blood, say sources.
Sources say it will now be investigated whether the fatal overdose was accidental or not.
Doctors had said on Saturday that Ms Tharoor died an "unnatural, sudden death". Some physical injuries on her body are believed to be unrelated to her death, say sources.
Mr Tharoor, the minister of state for Human Resource Development, recorded his statement on Sunday before the magistrate investigating his wife's death. Today, he will go to Hardwar to immerse the ashes of his wife, who was cremated on Saturday.
Mr Tharoor had earlier written to Home Minister Sushil Kumar Shinde offering "full and unstinted cooperation" in the investigation into his wife's death.(read) "I have finally had a chance to catch up with the media reports and am horrified to read the reckless speculation rampant there," he said in the letter, calling for a swift inquiry so the "truth can come out as soon as possible". (read letter)
The death of Mrs Tharoor was a tragic twist in a tale of apparent marital strife that played out on social media and was splashed across newspapers.
She was found dead on her bed at 9 pm by Mr Tharoor at the hotel they were staying in while their home was being painted. Earlier this week, she told the media that she had evidence of an affair between her husband and a Pakistani journalist, to whom she sent a series of angry tweets.
On Thursday, the Tharoors tried to end the controversy by issuing a statement saying they were "happily married."
Mrs Tharoor's iPad and iPhone have been taken as forensic evidence by the police. Investigators are examining the CCTV footage at the hotel and the staff is also being questioned.
They married in 2010 in what was described as a fairytale wedding; it was the third marriage for both. Four months before that, Mr Tharoor had to quit his first ministerial post after allegations that a Rs. 70-crore stake given to his wife in the Kerala franchise of the IPL was actually a payment to the minister for arranging the sale of the team from his home.