An American citizen whose meticulous scouting reports aided the 2008 Mumbai assault was sentenced to 35 years in prison by a U.S. judge on Thursday, the Department of Justice announced.

David Coleman Headley, 52, helped 10 gunman operating on behalf of a Pakistani militant group in the assault of a crowded train station, a Jewish center, and the landmark Taj Mahal Hotel on Nov. 26, 2008. In all, 164 people were killed in the attacks, including six Americans.

Headley, a U.S. citizen partly of Pakistani descent, was sentenced by U.S. District Judge Harry Leinenweber. Headley pleaded guilty in March 2010 to all 12 counts brought against him following his arrest in October 2009 as he was about to leave the country.

Headley admitted that he attended training camps in Pakistan operated by terrorist group Lashkar-e-Taiba five times between 2002 and 2005. In late 2005, Headley received instructions from three members of Lashkar to travel to India to conduct surveillance, which he did five times, according to a DOJ release .

Headley told authorities he attended several training camps operated by Lashkar including a three-week course on the merits of waging jihad; a three-week course on weapons and grenades; a three-month course on close combat tactics, the use of weapons and grenades, and survival skills; a three-week course on counter-surveillance skills; and a three-month course on combat and tactical training.

Headley eventually made five extended trips to Mumbai. Each time, he made videotapes of potential targets, including those attacked in 2008. Before each trip, Lashkar associates gave Headley specific locations to conduct surveillance. After each trip, Headley traveled to Pakistan to meet with Lashkar associates to report on the results of his surveillance, and provide the surveillance videos.

Before the April 2008 surveillance trip, Headley and Lashkar associates discussed potential landing sites in Mumbai for a team of attackers who would arrive by sea. Headley returned to Mumbai with a global positioning system device and took boat trips around the Mumbai harbor and entered various locations into the device, according to the DOJ.

Headley was convicted of multiple charges including conspiracy to bomb public places in India; conspiracy to murder and maim persons in India; six counts of aiding and abetting the murder of U.S. citizens in India; conspiracy to provide material support to terrorism in India; and conspiracy to provide material support to Lashkar.

Prosecutors asked for a relatively lenient sentence for Headley, citing the valuable intelligence he provided about terrorist networks following his arrest.

Related:

Mumbai: What Law Enforcement Learned

Mumbai: You Would Have Shot Back

What Does Mumbai Mean for Us? (Part 1 of 2)

What Does Mumbai Mean for Us? (Part 2 of 2)