Tejshree Thapa, a human rights lawyer who helped to expose the scope of mass rapes in the war-torn Balkans and South Asia and to build the legal arguments for the prosecution of those rapes as crimes against humanity, died on Tuesday in Manhattan. She was 52.

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

Ms. Thapa, who was born in Nepal and based in The Hague, had spent 11 years, including the last nine, as a senior researcher with the nongovernmental organization 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.”