India is building a legal case for access to a Chicago man who pleaded guilty to helping plan the 2008 Mumbai attacks, official said on Thursday, after confusing US signals on whether Indian police could quiz him. New Delhi says it could get more information on militant networks targeting India if it was allowed to interrogate David Headley, who admitted in a US court last week that he scouted targets for the attacks, which killed 166 people. But India's hopes of accessing Headley, 49, have so far met with frustration following contradictory statements from U.S. diplomats, threatening to strain relations with Washington. US Assistant Secretary of State Robert Blake said during a visit to New Delhi last week that Indian investigators would get access to the Chicago man. Two days later, US Ambassador to India Timothy Roemer said Washington was still to make a call. U.K. Bansal, a senior Indian internal security official, said that a meeting was held this week with legal experts to prepare the ground for approaching the US justice department. “The home (interior) ministry is working on documents seeking quick access to Headley,” an official from the law ministry said on condition of anonymity because of the sensitivity of the case. Indian officials also told US counter-terrorism coordinator Daniel Benjamin in New Delhi this week that India had a right to interrogate Headley and try him in an Indian court, government officials said. India has extradition and legal cooperation treaties with the United States that could come into potential conflict with Headley's plea agreement, under which he will be spared death sentence and extradition to India, Indian legal experts say. “This is a matter we need to press hard,” India's Law Minister Veerappa Moily told reporters on Wednesday. “We have to make a strong case, which we have already made.” Relations between India and the United States, which were on opposing sides of the Cold War, have warmed in recent years and the signing of a landmark 2008 civilian nuclear deal has elevated ties to a strategic level. But irritants have remained, including a nagging worry in New Delhi that Washington favors Pakistan in its war on terrorism. Also, a failure to remove Indian domestic policy hurdles that prevent U.S. nuclear firms from accessing India's estimated $150 billion nuclear power market has frustrated Washington. Indian officials said they will “soon” formally write to the US justice department seeking access to Headley, who spent his childhood in Pakistan and whose father is Pakistani.