In court documents, prosecutors have laid out details of his surveillance in India on behalf of Lashkar-e-Taiba and another militant group in planning the Mumbai attack.
American David Headley pleaded not guilty on Wednesday to US charges that he scouted targets for militant Pakistani group Lashkar-e-Taiba, blamed for the attack on Mumbai in 2008 that killed more than 160 people.
Headley, 49, has been cooperating with US investigators since his arrest in October.
In court documents, prosecutors have laid out details of his surveillance in India on behalf of Lashkar-e-Taiba and another militant group in planning the Mumbai attack and details of another plot against a Danish newspaper.
Denmark's Jyllands-Posten newspaper published cartoons in 2005 depicting the Prophet Mohammad that offended many Muslims.
Lashkar has been blamed for the Mumbai attack that killed 166 people, including six Americans.
The group has previously been associated with the dispute over Kashmir, a region split between India and Pakistan, but has a large network of support among Pakistanis around the world, raising fears it could attack Western targets.
India has refused to resume peace talks with Pakistan and sought to bring international pressure on Islamabad to act against militants operating from its soil, including Lashkar.
Pakistan is also under pressure from the United States, which wants it to root out Taliban fighters to help put down the insurgency in neighbouring Afghanistan.
Headley, who was born in the United States but spent several years in Pakistan, has previously pleaded not guilty to similar charges.
His accused co-conspirator, 49-year-old Pakistani-born Chicago businessman Tahawwur Rana, entered a not-guilty plea on Monday to charges he provided material support to the plots and to Lashkar.
Two Pakistanis have also been charged in the newspaper plot but are not in US custody.
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