"There is no political pressure on the case. An absolutely impartial inquiry is being conducted on the issue. In fact the Delhi police always conduct an impartial inquiry," said Singh.
Last week, the Delhi Police had issued a legal notice to Shashi Tharoor asking him to join the murder probe of his wife Sunanda Pushkar at the earliest.
A Special Investigation Team has been formed to carry forward the probe in the case.
Delhi Police told a TV news channel that her death was an "open-and-shut case" while adding Tharoor is likely to be questioned over why he forced the doctors to change opinion in the case.
They say there are several contradictions between people examined and Tharoor's statements.
Delhi Police Commissioner BS Bassi told CNN-IBN that a special investigation team may question Shashi Tharoor in the next few days.
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 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 Shashi Tharoor.
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