Three European researchers have embarked on the gargantuan task of establishing that the IS crimes aimed to systematically wipe out an ethnic group, in a bid to push the international community to halt the brutal crimes.
"We are not seeking to be sensational but to establish the stages of the criminal process for each category of the Yazidi -- men, women, children -- in order to back up the claim of genocide," Andrej Umansky, criminal law specialist at Cologne University, told AFP.
The Yazidis are neither Arabs nor Muslims and have a unique faith which IS jihadists consider to be heretical and polytheistic. The Kurdish-speaking minority is mostly based around Sinjar mountain in northern Iraq.
When the jihadists made an unexpected push in August last year into parts of northern Iraq under Kurdish control, the Yazidis were the worst hit, with many massacred and abducted.
The small European team from Yahad In Unum -- an association that collected evidence of Nazi slaughters of Jews and Roma in former Soviet areas -- has travelled to collect evidence at a Kurdish refugee camp just 20 kilometres (12 miles) from the frontline where battle was raging with IS militants.
Since August, they have filmed 50 interviews with Yazidi men, women and children who have managed to flee the terror of IS.
While the witness accounts could be used to back up future legal proceedings, "our first aim is to stop this crime" which is still being perpetrated, said Umansky.
"Imagine if we had questioned the escapees of Auschwitz in 1942: reacting with legal procedures would not have been the priority."
CHILD SOLDIERS, SEX SLAVES
The initiative began last year following a meeting in Belgium with three Yazidi refugees, said Costel Nastasie, a Belgian former police officer who specialised in investigations of crimes against the Roma.
The team's small size and French foreign ministry backing helped open the doors to the Kurdish refugee camps.
The greatest challenge has been finding recent Yazidi arrivals who clearly recollect the crimes and are willing to talk about their traumatic experiences.
"Most people are very emotional, there have to be frequent breaks," said Nastasie.
"And we have to explain to the victims' family members why we have to be in a room alone with the person.
"Some women are willing to speak in front of us, but others would only remain with our Yazidi investigator."
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UN investigators have said that the IS jihadists appeared to be committing genocide against the Yazidis.
The jihadists themselves have called in their magazine Dabiq for fighters to "kill (them) wherever you find them, and capture them, and besiege them".
They have also said the Yazidi women "could be enslaved".
For French priest Patrick Desbois, the "organised and administrative" characteristic of these crimes "in different places that are far from each other (is) astounding".
And it is this characteristic that might qualify the violations as genocide -- crimes committed against a specific group of people with the intent of destroying them.
Such violence can include killings, causing mental harm, imposing measures to prevent births, or forcibly transferring children to another group.
'EVERYONE IS REGISTERED'
The Kurdistan Regional Government (KRG) in August said there were 550,000 Yazidis in Iraq -- but they also account for 400,000 of the more than three million people displaced in Iraq since the IS violence erupted in early 2014.
According to the KRG, 1,280 Yazidis were killed in the IS offensive, 280 died from conditions they were subjected to and 841 remain missing.
More than 5,800 were abducted by IS, of whom just over 2,000 had managed to flee, the KRG said.
Witnesses have spoken of a shockingly orderly process in which "everyone is registered" by the IS, and where the jihadists obsessively sought to obtain their captives' documents.
Desbois said IS medical experts were present at all stages of the process -- to check women's virginity, to drug sex slaves, and to force young boys to swallow painkillers during military training.
He also said that when young Yazidi refugees watched IS militants speaking in propaganda videos, "the young people knew them all, showing how important indoctrination was in the training camps".
The investigators are also looking into how the IS has snatched babies on the pretext of giving them a new life in a Muslim family.
"It's possible that these children are sold to Qatari or Saudi families," said Nastasie.
The process of identifying perpetrators looks promising, as many jihadists do not bother to hide their faces and are also often known at least by their nicknames, said Umansky, who said he was stunned by how people from all over the world had joined the IS.
As they try to piece together precise information about the training of child soldiers or the sale of abducted women, the investigators are struggling with the fact that the victims are spread out over a large geographic area -- also a problem for any potential rescue operations.
"The Yazidis are in the lives of the IS -- in their prisons, in their families, next to fighters over a vast territory," said Desbois.