At least 9,900 of Iraq's Yazidis were killed or kidnapped in just days in an Islamic State attack in 2014, according to the first study to document the number of Yazidis affected which could be used as evidence in any trial for genocide.
About 3,100 Yazidis were killed - with more than half shot, beheaded or burned alive - and about 6,800 kidnapped to become sex slaves or fighters, according to the report published in the Public Library of Science journal PLoS Medicine on Tuesday.
In August 2014, Islamic State militants launched an assault on the Yazidi religious community's heartland in Sinjar, northern Iraq, home to around 400,000 Yazidis.
"Until now, there has not been clarity on the numbers of Yazidis killed and captured by ISIS during the attack on Mount Sinjar," said lead researcher Valeria Cetorelli, a demographer from John Hopkins University and the London School of Economics and Political Science.
"What we wanted to do, in anticipation of a possible trial, is provide the best estimates that we can get of the people affected," she told the Thomson Reuters Foundation.
Thousands of captured men were killed in what a United Nations commission called a genocide against the Yazidis, a religious sect whose beliefs combine elements of several ancient Middle Eastern religions. Islamic State considers them devil-worshippers.
Legal experts have said gathering evidence of the attacks is crucial since members of the Islamist militant group, also known as ISIL or ISIS, could go on trial for genocide in the future.
International human rights lawyer Amal Clooney last June said she aimed to prosecute the Islamist group through the International Criminal Court for their crimes against the Yazidi community.
U.N. investigators estimate more than 5,000 Yazidis have been rounded up and slaughtered and some 7,000 women and girls forced into sex slavery.
Cetorelli said she spent three months in 2015 interviewing a random sample of 1,300 surviving Yazidi families in Iraqi camps, and found at least 2.5 percent of the minority group were killed or enslaved.
"Our findings are really consistent with other evidence, for example, what is being found in mass graves or accounts from survivors, people who managed to escape captivity," Cetorelli said.
"So all this together can really help support a formal genocide investigation by either the International Criminal Court or another appointed judicial authority."
Iraqi forces are now fighting to retake the city of Mosul, the militants' last major stronghold in Iraq, where many Yazidis were held.