Mass graves of ISIS victims discovered across Iraq and Syria

Documenting atrocities committed by the Islamic State can seem impossible. A new report from the Associated Press, however, catalogs 72 mass graves around Syria and Iraq -- including one site that held 1,700 bodies. Gwen Ifill speaks with the AP's Lori Hinnant about the locations of these burial sites, what happened to the victims entombed within them and whether anyone is being held responsible.