In a hostile corner of southern Afghanistan, an American platoon fanned out around a market, forming a protective circle around a petite woman with a notebook. Paula Loyd, a Wellesley-educated researcher, began interviewing villagers about the price of cooking fuel - a key indicator of whether insurgents had hijacked supply lines.

Paula Loyd, June, 2006 As part of a new military program that uses social scientists to improve the troops' understanding of the local population, Loyd began interviewing a gregarious stranger who approached her with a jug of cooking fuel in his hands. He talked for 15 minutes, thanking her profusely in English. But just as her guards motioned it was time to leave, he lit his jug on fire and engulfed the 36-year-old Loyd in flames.

Minutes later, her fellow researcher shot and killed the man, adding a violent coda to a case that has already increased debate about the worsening conditions in Afghanistan and the military's attempt to use social science to cure insurgency.

The attack on Loyd, who died in a Texas hospital on Jan. 7 after a two-month struggle for her life, has reverberated from the Wellesley campus, where people grieve for the energetic scholar who seemed to be a natural peacemaker, to national academic circles, where anthropologists carry on a heated debate over whether social scientists should be working for the military, to the Afghan mountains, where soldiers vow to give meaning to her death by fighting on.

"There are bad people out there who didn't want Paula to succeed," said Steve Fondacaro, a retired colonel who runs the Human Terrain Systems program, a $250 million Pentagon initiative that has dispersed six teams of researchers - with two social scientists per team - to work with military units across Afghanistan.

Loyd's death - the third among the researchers - "just highlights the need for us to continue the mission," he said.

But elsewhere, the attack has revived a bitter debate about whether anthropologists should ply their trade for the military.

In 2007, just months after the Human Terrain program was launched, the American Anthropological Association declared that it violates the group's code of ethics, which stipulates that subjects of study must not feel forced to participate and must never be harmed. On Feb. 15, the association will vote on a new resolution that would prohibit research that is not made public, a move targeting research for both military and industrial purposes.

"You can't really do anthropology in a group of people with guns," said Sally Engle Merry, Loyd's senior thesis adviser at Wellesley, who has served on the board of the American Anthropological Association.

"This has been a very painful thing to me," Merry added. "On the one hand, I think Paula was absolutely right to give the military a way to understand the lives of Afghans better. On the other hand, what happens to the information you gather? Who owns it? How is it being used?"

Adding to the controversy has been the fate of Loyd's attacker, identified in court documents as Abdul Salam, who tried to flee on foot. Don Ayala - the leader of Loyd's Human Terrain team - knocked him down and handcuffed him. Minutes later, when Ayala learned how seriously Loyd had been hurt, he put a pistol to the man's head and fired, according to an affidavit filed in a Virginia court where Ayala pleaded guilty last Tuesday to manslaughter.

To Loyd's Army buddies, the story of death and vengeance serves as proof of the need to continue fighting until the enemy is defeated.

"Immediate justice was served," Thad Santon, a self-described Army friend of Loyd's, wrote on her prayer website.

But others point to the incident as evidence that the Human Terrain program and the US military mission in Afghanistan itself have gone awry.

"Salam got murdered in his own country by foreign occupiers," Maximilian C. Forte, assistant professor of anthropology at Concordia University in Quebec, wrote on his website, Open Anthropology. "Try, just as an experiment, to see things from that angle for a moment."

This is how Paula Loyd's friends at Wellesley remember her: Chugging wine from the bottle in a Somerville apartment. Dressed as GI Jane for Halloween. Some years her blond hair flowed down her back. Other years it was short as a boy's. She was hard-core at everything she did. She read "Don Quixote" in Spanish. She rose at 4 a.m. to row the Charles River.

"She was a true anthropologist," said Gretchen Wiker, a friend of Loyd's since the fifth grade. "You would go to a restaurant, and she was the one who knew the bartender and the waitress. You'd go to the beach, and she'd know the bus driver. She was such an open person, and approached people with such an open heart."

Raised in San Antonio, Loyd moved to the island of St. Thomas at age 12 with her mother. She was curious about living in a foreign culture, said her mother, Patricia Ward.

Concerned that an island education would prevent her from getting into a good college, her parents sent her to boarding school at Choate Rosemary Hall. Later, she joined Wellesley's class of 1995.

Her freshman year, she took an anthropology class that sent students to do ethnographies of Boston neighborhoods. Some balked at the idea of talking to strangers, but Loyd loved it.

"She really stood out in the class as an amazingly poised student and sophisticated thinker," said Merry, now professor of anthropology at New York University.

But instead of pursuing a graduate degree in anthropology, Loyd enlisted in the Army - a rare decision for a Wellesley grad. Military recruiters pushed her to go into the officer corps, but she refused. She didn't want to sit behind a desk.

"She wanted to understand the Army from the ground up," said Dr. Alexis Meshi, a Wellesley classmate. "It was just her wanting to understand how things work in a very basic level, not being treated in any special way."

Loyd became a tank mechanic, working for four years in South Korea and at Fort Bragg, N.C. She enrolled in a master's degree program at Georgetown University, but joined the Reserves, serving with the 450th Civil Affairs Battalion. In 2002, she was thrilled when they were called to Afghanistan.

"She was always up for a new adventure," her mother said. "And there was so much hope for the country then."

In Kandahar, Loyd led a team that tried to dig wells and build roads in isolated villages. She sought to understand cultural norms, even as she defied them. She wore her blond hair tucked up in a helmet, not under a burqa, as local women do. Serving in a mostly male Army and a country dominated by men, she often stood out as a female in charge.

"Sometimes I'll be talking to the men in a village and they'll turn to the interpreter and say, "Is that a man or a woman?' " Loyd was quoted as saying in Pennsylvania's Morning Call newspaper in 2003.

She spent hours drinking tea with tribal elders, according to her Afghan interpreter at the time, who asked to be identified only as Farid because of security reasons.

"Paula was very popular," he said in a telephone interview. "People were really optimistic and they had hopes that these teams would help them."

When Loyd's unit went home, she stayed on in Afghanistan as a civilian, taking jobs with the International Organization for Migration and the United Nations. In 2004, she joined the Provincial Reconstruction Team in Zabul as a USAID worker, arriving during a terrible winter. As snow blocked roads and people died of disease, Loyd's swift acquisition of food, hats, boots, and socks to distribute among the freezing population earned her a USAID award.

But by 2006, the situation in Afghanistan was deteriorating. Corruption was rife, and some Afghans began to see NATO troops as occupiers rather than liberators. US casualties climbed, as did Afghan deaths from both insurgent attacks and US bombings and raids. NATO soldiers could not be defeated, but neither could they decisively win.

When seven contractors working for an American organization were killed in Zabul, Loyd helped ship their bodies home.

That summer, she told a panel in Washington that bringing stability to Afghanistan would require a long-term commitment. "The current wisdom is 15 to 20 years," she said.

Desperate to turn the tide in Afghanistan, the military launched the Human Terrain program in February 2007. General David Petraeus, the new commander who specialized in innovative counterinsurgency tactics, became convinced that the military needed a deeper understanding of the country, from tribal rivalries to village economics. After the first batch of anthropologists arrived in February 2007, US commanders reported that the new program had helped them reduce their combat operations by 60 percent.

But others were skeptical that useful research could be done in such a hostile environment, or that the population would see the scientists as noncombatants.

"This is a country where during the day they speak like they are great friends and at night they become the Taliban movement," said a European diplomat who asked not to be named. "Even if you are an expert, it's difficult."

Afghanistan had taken a toll on Loyd. She bought a house in North Carolina and told friends she was recovering from post-traumatic stress syndrome there, according to Stefanie Johnson, a classmate from Choate and Wellesley.

"She was looking to settle down, lead a normal life," Johnson said, adding that she hoped to marry Lieutenant Colonel Frank Muggeo, a former special forces commander she had met in Afghanistan who is now in charge of the Army Marksmanship Unit at Fort Benning in Georgia.

But, last year, Loyd decided to take "one last tour," Johnson said.

She joined the Human Terrain initiative, helping to develop some of its protocols. She was well aware of the controversy surrounding it, but she "believed in the program," said Wiker, her childhood friend. "She would not have gone there if she did not believe that she was doing something useful and positive for the people there."

She trained for four months with her research team, which included Don Alaya, a former bodyguard for Afghan president Hamid Karzai, and Clint Cooper, a Marine who had served in Iraq. The three became close friends, Fondacaro said.

In fall 2008, they made their way to a US military outpost in Maiwand, a strategically important transit point on the route between Kandahar and Helmand, an insurgent stronghold.

Fondacaro said that Loyd's job was to perform rapid "ethnographic studies" for her military unit, writing brief sketches describing the local population. He insists that she was acting as a social scientist, not a soldier, and that her reports were research, not intelligence, even though none has ever been made public.

"This is about social science, field research capacity," he said. "You could eventually teach a soldier to do it, but it would take years."

When Paula Loyd was set on fire on Nov 4, 2008, Cooper, her teammate, rushed to submerge her in water and stayed by her side during the long flight home to a hospital in Texas. Loyd kept her sense of humor. When she was told she would be transported to an emergency plastic surgeon, she joked, "I've always wanted to get a few little things done," according to an account published on the Human Terrain website.

For two months, as Loyd struggled for her life with burns covering 60 percent of her body, an eclectic band of Army buddies, Wellesley classmates, and Afghan friends consoled one another.

"I am associated with you in this moment of sorrow, and want great penalties for the enemies of Paula," Delbar Jan Arman, the governor of Zabul, wrote to Loyd's mother in Texas.

"Paula, thank you for being my friend," wrote a fellow reservist on a prayer website. He wrote that he had once believed that women were unfit for combat - but then he met Loyd.

"I was blessed to serve with this female soldier in the combat theater of Afghanistan and here in the US," he wrote. "She was one of the finest individual persons I have ever known."

On the same website, Farid wrote: "You are in my prayers five times a day."

When she died, people from all walks of life traveled to her funeral, including Ayala, who was embraced by Loyd's Wellesley friends.

"It's a complicated situation - he shot a person and killed him, but for us, we felt that this person was looking out for her," said Ophelia Navarro, a former classmate. "We are hurting and grieving, and he also was hurting and grieving. He said that they were the best team because Paula was so professional, had this complete brilliant understanding and interaction with people."

Loyd's mourners have also had to deal with controversy over the program she served in. Some blogs that announced her death featured debates about whether she was a legitimate military target.

"These aren't just social scientists," wrote a commenter named Eric O on Wired magazine's blog, Danger Room. "They are employed by the US military to conduct research with a goal of helping the military more effectively carry out the occupation."

For Loyd's loved ones, such comments make her death more painful.

"We are very upset that people were using her for political gain," said Meshi, a Wellesley classmate. "They portrayed her as this really naive woman who did not know what she was doing, or used it as a way to criticize the Human Terrain program."

But Loyd's friends and relatives don't have time to dwell on anger. They are too busy trying to figure out how to carry out her last wishes. In her will, Loyd asked that a fund be set up to send Afghan girls to Wellesley. Loyd's mother isn't sure how to do that, but she is planning to travel to Afghanistan to figure it out. "We want to continue what she was doing," she told the mourners at Loyd's memorial. "We want to make sure her legacy stays alive."

 Globe correspondent Jillian Jorgensen contributed to this report.