The 105-page report presents evidence that the civilians were killed on August 4, the first day of the operation. Two opposition groups that took part in the offensive, the Islamic State of Iraq and Sham and Jaish al-Muhajireen wal-Ansar, are still holding the hostages, the vast majority women and children. The findings strongly suggest that the killings, hostage taking, and other abuses rise to the level of war crimes and crimes against humanity, Human Rights Watch said.