Headley's meticulous scouting missions had facilitated the assault by 10 gunmen from a Pakistani-based militant group.
"I don't have any faith in Mr Headley when he says he's a changed person and believes in the American way of life," said US District Judge Harry Leinenweber in imposing the sentence, which was in the range of what prosecutors had requested for Headley's widespread cooperation. (Have no faith Headley is a changed person: Judge)
The attackers arrived by boat on November 26, 2008, carrying grenades and automatic weapons, and fanned out to hit multiple targets, crowded train station, a Jewish centre and the landmark Taj Mahal Hotel. TV cameras captured much of the three-day rampage live.
Before Judge Leinenweber imposed the sentence, a victim shot in the attack gave emotional testimony during the hearing. Linda Ragsdale, a Tennessee children's author, spoke through tears describing how she lost friends in the attacks and her own injuries. She said she was haunted by the sounds of people suffering and her recovery from the wounds continues.
"I know what a bullet can do to every part of the human body," she said. "I know the sound of life leaving a 13-year-old child. These are things I never needed to know, never needed to experience." (Headley has no right to live: kin of US victims)
The attack heightened the strain in a historically antagonistic relationship between India and Pakistan; the two countries have fought three major wars. Indian officials have accused Pakistani intelligence of helping to plan the assault - an allegation Pakistan denies.
Late year, India secretly hanged the lone surviving gunman, Mohammed Ajmal Kasab.
Citing what they described as valuable intelligence Headley provided authorities about terrorist networks since his arrest, prosecutors had asked for a relatively lenient sentence of between 30 and 35 years.
The charges included conspiracy to aid the Pakistani-based group, Lashkar-e-Taiba, or the Army of the Pure, that mounted the attacks, as well as conspiracy to commit murder in India, and aiding and abetting in the murder of six Americans.
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