The US interlocutors have cited Headley's plea bargain with the American authorities (under which a person avoids death penalty by confessing to the crime) and indicated its difficulty in allowing Indian investigators to further question Headley who had carried out the recce of the 26/11 targets for the Pakistan-based terror outfit Lashkar-e-Taiba, official sources said.
However, India may be allowed to question Headley's accomplice Tahawwur Hussain Rana who helped his childhood friend to recce the 26/11 targets.
Indian investigators believe that if they could quiz Pakistani-Canadian Rana, many information could come to light as he was a close associate of his Pakistani-American friend Headley.
The investigators believe that Headley and Rana have a lot of information and their interrogations could throw more light on the conspiracy hatched to carry out the worst terror strike in India and role of those behind it.
Indian investigators had questioned Headley in 2010.
Headley had pleaded guilty to 12 terrorism charges, including his involvement in the November 2008 terror attacks in Mumbai that claimed 166 lives. He had, however, entered into plea bargain with US authorities.