New Delhi's request for access to Headley's wife Shazia Gilani, his girlfriend Portia Peter and one more female friend is yet to be acceded by Washington.
Notwithstanding America's refusal to extradite Headley, India will continue to press for 52-year-old Pakistani-American terrorist, who carried out recce of the 26/11 targets for terror outfit LeT, Home Ministry officials said.
US Attorney Gary S Shapiro testifying before an American court on Tuesday ruled out extradition of Headley under a guilty plea that he had entered into with the US government.
New Delhi is, however, hopeful of getting access to Headly's Pakistani-Canadian friend Rana, who helped him to carry out his nefarious design in India, as Washington has given indication in this regard.
"We have been assured access to Rana and we hope to question him soon. A formal request for questioning Rana has been sent to the US," an official said.
On India's request for questioning Headley's wife Shazia, his girlfriend and another female friend, the US has conveyed that without the consent of the persons concerned, it is not possible to give any commitment as American law does not allow forcible questioning.
"So, we are seeking their consent to quiz them," the official said.
Though India had limited access to Headley, it has not been able to question Rana so far.
External Affairs Minister Salman Khurshid had last month had written to his US counterpart Hillary Clinton requesting for extradition of Headley and his accomplice Rana.
A Chicago court, on January 17, sentenced Rana to 14 years in jail followed by five years of supervised release for providing material support to Pakistan-based LeT and for backing a "dastardly" plot to attack a Danish newspaper.
The US court, however, did not find him guilty in 26/11 terror attack case.
Headley, who "unquestionably contributed" to the Mumbai attack that claimed 166 lives, is set to be sentenced by a Chicago court tonight, with US government seeking a lighter 30-35 year jail term for him as he provided "valuable" information about the militant outfit.