The following information is from a Russia Today article:
The Associated Press has gathered documents and testimonials to produce a picture of widespread atrocities in Iraq and Syria where 55 ISIS mass graves have been located in Syria and 17 in Iraq, containing as many as 15,000 victims.
The information came from a satellite intelligence firm named AllSource that matches photos from space with eyewitness accounts, and also from aid groups such as Yazda, and often from ISIS itself that brags about its atrocities of killing “infidels” and “traitors.”
An investigator for the Iraqi Kurds said, “They are beheading them, shooting them, running them over in cars, all kinds of killing techniques, and they don’t even try to hide it.”
The biggest known massacre was committed in Tikrmt in June 2014, when ISIS gunned down up to 1,700 unarmed Shiite Iraqi Air Force recruits, forcing them to shout slogans as they laid down waiting to be executed. Thirty-six of the perpetrators were hanged for the war crime earlier this month. Another similar massacre also happened two days earlier near Ramadi as described by survivors who played dead and escaped during the night with 15 others.
With the war still ongoing in many areas such as Hardan, which is a Kurdish area, the authorities have only roped off the mass graves for excavating the dead in the future when resources will exist to do so, currently leaving the bodies exposed to the elements, to the horror of local villagers.
Since ISIS is enemies with different sects such as Shia and Yazidis, and different ethnicities such as Kurds, and even certain Sunni tribes, there are estimated to be hundreds of mass graves that will take years to be fully mapped for their victims to be given a proper burial.
“This is a drop in an ocean of mass graves expected to be discovered in the future in Syria,” said Ziad Awad, who is cataloging the ISIS massacres.