"He knows what happened and he should disclose it. I know that he was involved in the incident. I am not saying that he killed her, but he knows who has. Also, I said he knows who the murderer is, I did not say I know who it is," said Swamy.
Tharoor had earlier on Tuesday dared Swamy to speak up the name of the murderer. "Who is he? If he knows the murderer, then let him tell the police," said Tharoor.
The Delhi Police had earlier issued a legal notice to Tharoor and asked him to join the murder probe of his wife at the earliest.
Sunanda, who married Tharoor in 2010, had checked into The Leela Hotel in Chanakyapuri a day before her death on January 17, 2014.
Tharoor's aides said the couple had checked into the luxury hotel because of renovation work at his New Delhi bungalow.
Prior to her death, Sunanda was embroiled in a spat with Pakistan-based journalist, Mehr Tarar, whom she accused of stalking her husband.
Image: Congress leader Shashi Tharoor with wife Sunanda Pushkar
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If Swamy knows Sunanda's murderer, let him tell police: Tharoor