The United Nations reports at least 535 people were killed, and tens of thousands displaced, in western Congo over a 3-day period in December, in what could amount to crimes against humanity. U.N. investigators say the chiefs of opposing factions helped plan and carry out the violence in response to an alleged territorial dispute, and local authorities failed to intervene to protect residents. The U.N. warns that more acts of violence are likely unless the government acts to ease tensions between rival factions.