ISIL jihadists have tried to justify seizing thousands of Yazidi women in northern Iraq and offering them to fighters as sex slaves.
When stories of mass murder and enslavement first emerged in August there were suggestions they might be exaggerated.
Now, however, researchers who have talked to survivors and imprisoned women on hidden mobile phones believe that up to 5,000 men may have been shot dead and bulldozed into mass graves, and 7,000 women held in detention centres to be offered as slaves.
Moreover, the Islamic State of Iraq and the Levant has not only admitted taking the women, but issued a lengthy theological justification.
"After capture, the Yazidi women and children were then divided according to the Sharia amongst the fighters of the Islamic State," says a new article in their English-language online magazine Dabiq.
When the jihadists attacked areas occupied by Yazidis, the West's attention focused on tens of thousands of refugees who crowded the barren hills of nearby Mount Sinjar. But thousands more were captured in nearby villages.
"My 13-year-old sister was separated from my family," said one man, Ahmed Naif Qasem, who is staying in the town of Ba'adre. His parents, wife and extended family were seized from their home in Snuny, near Sinjar, and taken over the Syrian border to be converted to Islam at gunpoint.
When the family returned, his sister and his wife had been taken away. His wife was later allowed to rejoin her family after having been "treated badly", but no one had seen his sister since.
What has happened to the women has been relayed in a series of phone calls from families, and in some cases by women and girls who managed to escape.
Bakat Khalaf, 60, another refugee in Ba'adre, said his 13-year-old niece had escaped seven weeks after being "taken away" but had so far been too distressed to describe what had happened to her.
"She just cries when she tries to speak," he said. Others escapers have told of being "married" to older jihadi leaders, in some cases raped, and made to watch acts of barbarity. Such stories have been confirmed by researchers from the United Nations. Matthew Barber, a scholar of Yazidi history at the University of Chicago who was in Kurdistan as the assaults happened, said he had a list of 4,800 names of women and children being held captive.
"In every place where Yazidi women or families are held, jihadists come and randomly select women that they take away," he added. "A final total above 7,000 is perfectly feasible."
The town of Tal Afar alone is thought to hold around 3,500 women and children in five detention centres. Others are being held in Mosul.
Much of the Islamic State newsletter is devoted to theological justifications for the jihadists' behaviour, citing the practices of the Prophet Mohammed and his Companions.
The article about the Yazidis, entitled "The Revival of Slavery before the Hour", says that "well-known" rules are observed, including not separating mothers from their children.
The Dabiq article does not specifically say women are being sold for sex, but it says taking a maid as a concubine helps men avoid the sin of adultery, or of being alone with an unrelated woman. An open letter to Isil by Islamic scholars last month took them to task over the Yazidis, insisting that: "The reintroduction of slavery is forbidden in Islam. It was abolished by universal consensus."
The figures for men killed as Isil took their villages are reminiscent of the Srebrenica massacre in the Bosnian civil war. The UN's report says 250-300 men were killed in Mr Khalaf's village, Hardan, including 10 by beheading; another 400 were gunned down in the village of Khocho; another 200 civilians were killed by Isil shelling them as they left the village of Adnaniya; as another group of refugees reached the village of Qiniyeh, the men were separated from the women and children, and 70 to 90 of them were lined up by a ditch and shot.
On another road, witnesses reported dozens of bodies left behind, including those of four elderly men with disabilities, who had been shot dead.
In some massacres, the bodies were bulldozed into mass graves, survivors told The Daily Telegraph. In others, men were herded into Yazidi temples that were then blown up.
Mr Barber and Kurdish representatives said researchers believed 3-5,000 men had been killed.
The Yazidi religion is an offshoot of Zoroastrianism, and Yazidis are described as "devil-worshippers" by Isil.