Her family said she died at Mount Sinai Hospital of multiple organ failure.

Thapa, who was born in Nepal and based in The Hague, had spent the past 15 years as a senior researcher with the nongovernmental organisation Human Rights Watch. In 2017, she was among the first human rights workers to travel to the Bangladesh-Myanmar border and document the Myanmar military’s ethnic cleansing of Rohingya Muslims.

She made her mark in the 1990s as an investigator with the International Criminal Tribunal for the Former Yugoslavia. She headed a unit that investigated mass rape and sexual enslavement in Bosnia and Herzegovina and helped win the landmark Foca cases, named for the Bosnian town where sexual crimes were committed against Muslim women in 1992 and 1993.

Her work resulted in the convictions and imprisonment of eight Serb paramilitary leaders and their supporters. The Foca convictions upheld a precedent set in 1998 by a similar tribunal after the Rwandan genocide, which established rape as a crime against humanity, and they expanded the definition of crimes against humanity to include “sexual enslavement.”

“At the time, there was not a lot of established legal doctrine in this area,” John Sifton, an advocacy director for Human Rights Watch, said in a phone interview. “With the Foca cases, rape and sexual slavery were recognised as atrocities, among the most reviled of human behaviours. It was her work with victims and witnesses that helped make that happen.”

She also helped build the case against Slobodan Milosevic, the former president of Yugoslavia and later of Serbia who was known as “the Butcher of the Balkans.” He was tried on charges of genocide, crimes against humanity and other atrocities but died in 2006, before a verdict was returned.

After 15 years at the tribunal, Thapa joined Human Rights Watch in 2004. One of her early successes there was to help force the United Nations to acknowledge what it called its “systemic failure” in protecting civilians during the 26-year civil war in Sri Lanka, which left at least 100,000 people dead, including as many as 40,000 in the last five months of 2009, when the war ended.

Her work in documenting and revealing that failure helped lead to an internal U.N. investigation and a report with the blistering conclusion that “many senior U.N. staff simply did not perceive the prevention of killing civilians as their responsibility.”

The investigation prompted Secretary-General Ban Ki-moon to establish an initiative called Human Rights Up Front, which emphasised the importance of responding early to human rights violations as a prevention of genocide.

As an acknowledged expert on Sri Lanka, Bangladesh and Nepal, Thapa wrote numerous reports regarding atrocities, disappearances and travesties of justice. Many of those reports were released under the banner of Human Rights Watch, but Sifton said she was often the anonymous author.

In addition to the civil war in Sri Lanka, Thapa reported extensively on the 10-year civil war in Nepal, documenting widespread war crimes, crimes of sexual violence and other abuses perpetrated by both sides. She interviewed hundreds of witnesses, and her reports helped persuade Washington to cut its military aid to Nepal over human rights concerns.

She also attended countless hearings and participated in briefings in Washington, London, Brussels and Tokyo with high-level diplomats and officials. But she spent much of her time in the field with survivors of sex crimes, witnesses and families of people who had been killed or tortured or had disappeared. She earned their trust, recorded their experiences and stood by them as they testified in court against their abusers. She also stayed in touch with many of them long after her work was done.

“She was able to connect with families in an extraordinary way,” said Meenakshi Ganguly, the South Asia director for Human Rights Watch. “She handled them with so much empathy. At some point, most people in her position walk away. She never walked away.”

Tejshree Thapa was born on Nov 10, 1966, in Kathmandu. Her mother, Dr Rita (Basnet) Thapa, established maternal and infant care clinics in Nepal and campaigned for women’s reproductive rights. Her father, Bhekh Bahadur Thapa, held several positions in Nepal’s government, including foreign minister and ambassador to India and to the United States.

Her parents survive her, as does her daughter, Maya Thapa-O’Faolain, from a marriage that ended in 2005. (Another marriage also ended in divorce.) She is also survived by her sister, Manjushree Thapa, the author of several books set in Nepal. Her brother, Bhaskar, died in 2013.

When she was a teenager, Tej, as she was called, moved with her family to Canada, where her father worked for the International Development Research Center in Ottawa.

When her father was named Nepal’s ambassador to the United States in 1979, the family moved to Washington. She graduated from the National Cathedral School there in 1984.

She attended Wellesley College, graduating in 1988 with a degree in philosophy, and graduated from Cornell Law School in 1993.

Fresh out of law school, she went to work for Radhika Coomaraswamy, an international human rights advocate and the first UN special rapporteur (investigative expert) on violence against women.

Working with Coomaraswamy, Thapa travelled extensively, interviewing survivors and sometimes perpetrators. She gained the experience that would serve her throughout her career as she went on to prepare authoritative reports and brief diplomats around the world.

Recently, on the Myanmar border, she was doing what Human Rights Watch said in a tribute to her she did best: “Making sure that victims and survivors could tell their stories, and that policymakers could no longer ignore their suffering.”

© 2019 New York Times News Service