Bangladesh, Aug. 26 -- Bougainville stands at a historic crossroads. After decades of conflict and political struggle, the autonomous Pacific island region is moving closer to its long-sought independence from Papua New Guinea. Yet at the center of that ambition lies a deeply contentious question: who should control and develop Panguna, the giant gold and copper mine whose closure helped trigger one of the Pacifics bloodiest conflicts?

The mine, estimated to contain resources worth as much as $160 billion, could provide the economic foundation for an independent Bougainville. But an investigation by the Organized Crime and Corruption Reporting Project (OCCRP) has raised serious questions about the way President Ishmael Toroama selected a...