PERCHED ON THE NORTHEASTern edge of Bosnia, Brcko was once among the Ottoman Empire's farthest outposts. As one of the River Sava's largest ports, it was a fief of ferrymen who plied their craft from the south bank to Hapsburg-ruled Slavonia on the other side. The two empires are nearly 80 years in their graves now, and Brcko recently seems to have been the haunt of a more spectral ferryman: Charon, transporting the souls of thousands of murdered civilians across the Styx.
Telling evidence of mass graves around Brcko, and near the infamously conquered city of Srebrenica to the southeast, came...