War crimes investigators collecting evidence of the Islamic State group's operation to kidnap thousands of women as sex slaves say they have a case to try IS leaders with crimes against humanity. But the investigators cannot get the global backing to bring detainees before an international tribunal.

Two years after the IS onslaught in Iraq, the investigators, as well as U.S. diplomats, say the Obama administration has done little to pursue prosecution of crimes that Secretary of State John Kerry called genocide. Current and former State Department officials say the Defense Department blocked an attempt to have a legal finding of genocide, setting back prosecution efforts.

Officials say that the Defense Department and ultimately the administration were concerned that trials would distract from the military campaign.