Bassi said that Menon, who was out of India, has reached the national capital.

"He (Menon) was summoned. He has now reached Delhi. He will be joining our investigation, as per my information, sometime... today," Bassi told reporters here.

Bassi also said that Menon was out of India so he could not come earlier.

A police team probing the murder of Sunanda has questioned at least 15 people in connection with the case so far.

Congress MP Shashi Tharoor, his staff members and close friends were among those quizzed by the Delhi Police.

Former Samajwadi Party leader Amar Singh and senior journalists Nalini Singh have also been questioned by police.

52-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 over the latter's alleged affair with Tharoor.

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