The three-day slaughter in 2008 drew global attention because it targeted Westerners as well as Indians and implicated Pakistan's spy agency. The Inter-Services Intelligence Directorate (ISI) continues to protect the masterminds, according to Western and Indian counterterror officials. U.S. prosecutors indicted an ISI major in the deaths of the Americans: He allegedly provided funds, training and direction and served as the handler of David Coleman Headley, an U.S. reconnaissance operative now serving 35 years in a federal prison.

The 56-page West Point report is titled "The Fighters of Lashkar-e-Taiba: Recruitment, Training, Deployment and Death." Though it refrains from policy suggestions, there are implications for U.S. counterterror strategy. Lashkar's popularity and clout defy conventional approaches to fighting extremism, said co-author Christine Fair, a Pakistan expert at Georgetown University.

"When you have an organization that enjoys such a degree of open support, there are no options for U.S. policy other than counterintelligence, law enforcement and counter-terrorism targeting," Fair said in an interview.

Lashkar was founded in 1989 by Hafiz Saeed, its spiritual chief today, and other ideologues. The ISI deployed Lashkar as a proxy force against India, especially in the disputed Kashmir region. Although banned by Pakistan in 2002, the group still functions unmolested, the ISI provides funds, military training and arms, and ISI officers serve as handlers for Lashkar chiefs, according to Western and Indian investigations. The U.S. officially declared Laskhar a terror group in 2001.

The West Point researchers said they used "massive amounts of material that the group produces about itself" to analyze the trajectories of Lashkar fighters who were killed between 1989 and 2008. The researchers translated from Urdu the 917 biographies that appeared in four extremist publications, including one written by mothers of fallen militants.

Recruits often become holy warriors with the help of their families, which admire Lashkar's military exploits in India and Afghanistan and its nationalism and social service activities at home, the study says. Unlike other terrorist groups, Lashkar does not attack the Pakistani state.

The group's vast training camps have churned out fighters at an alarming rate. The study gives an estimate of between 100,000 and 300,000 total trainees. By comparison, a U.S. counterterror official told ProPublica he has seen figures as high as 200,000, though he put the number in the tens of thousands.

Most recruits examined in the study joined at about age 17 and died at about 21, generally in India or Afghanistan. Their backgrounds contradict "a lingering belief in the policy community that Islamist terrorists are the product of low or no education or are produced in Pakistan's madrassas," the report says.