Here are the latest developments in this story:
The injection mark has been classified as injury number 10 in a medical report. Police sources say this appears to be an injection mark. The Delhi Police chief has said that Ms Pushkar, 51, died of poisoning that was given either orally or injected.
Doctors conducting the autopsy had found 15 injury marks on Sunanda Pushkar's body, including a bite mark on one of her hands and minor bruises on her arms.
On Monday, the Delhi Police said it had registered a case of murder based on a new report from doctors at Delhi's All India Institute of Medical Sciences (AIIMS) who handled the post-mortem for Ms Pushkar after she was found dead at a five-star hotel in the capital in January last year.
Before she died, on Twitter, she accused her husband of having an affair with a Pakistani journalist, but then appeared on television with Mr Tharoor to say the couple's marriage was a "happy" one.
Mr Tharoor, 58, a parliamentarian from Kerala, is likely to be among those questioned in the next few days, police sources have indicated. The murder case does not name any suspect.
Mr Tharoor said on Tuesday that he is "stunned" at a murder case being registered in his wife's death. "Although we never thought of any foul play in the death of my wife, we all want that a comprehensive investigation be conducted and that the unvarnished truth should come out," he said, assuring the police of his "full cooperation."
Police sources said the latest medical report has new facts on the injuries found on Ms Pushkar's body, but the police chief did not elaborate on this in his comments to reporters.
The police said they had to register a case to be able to send Ms Pushkar's viscera samples abroad to investigate what poison caused her death; Indian labs have been unable to determine that.
Police sources said that the medical report, received on December 29, said the death seemed "homicidal," the first time, they said, that such a mention was made in a report from AIIMS, where Ms Pushkar's autopsy was conducted.
But Dr Sudhir Gupta, chief of the forensic department of AIIMS, has told NDTV that the report does not mention "homicide." He said the report only says that Ms Pushkar died of poisoning. Dr Gupta led the team that conducted Ms Pushkar's autopsy.
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