ON A RAINY November evening in 2021, a Congolese researcher took a call from a concerned American friend and mentor looking for assistance on a life-threatening mission. He needed help with a delicate investigation into deaths in Central Africa.

The researcher, a seasoned humanitarian worker and development project evaluator named Karume Baderha Augustin Gang, had collaborated with the American epidemiologist some 20 years back, when he helped conduct a mortality survey that revealed millions of deaths during a war in the Democratic Republic of the Congo. In retaliation for Karume’s involvement in that project, opposition forces had tortured the young researcher’s brother. But despite the risks of a similar investigation, Karume agreed to take part.