ISIS executed over 700 Iraqi soldiers in Tikrit in June of 2014 and the blood soaked ground was visible with satellite imagery.
The amazing photos were published by the Daily Mail on Thursday and shows mass execution sites which tripled the initial death toll estimated by experts. The photos helped build a case to prosecute two dozen ISIS militants implicated in the massacre, while hundreds are still at large.
Those apprehended were sentenced to death by an Iraqi court. Human rights experts were also able to identify raised earth, pointing to evidence of mass graves and earth moving equipment. Bulldozers were apparently used to cover the mass graves.
At least one witness who was able to escape confirmed to Human Rights Watch details and location of the massacre and helped provide evidence of a third mass grave.
The man, who goes by the name of Ali, was lined up with a group of ten other men that were shot with pistols. He says that somehow he was not hit, pretended to be killed, and waited for nightfall to sneak out under the cover of darkness.
Another witness told Human Rights Watch he saw the men being lined up and packed in trucks, although he is uncertain of the fate of the men he saw being taken away by ISIS fighters.
After conquering Tikrit in 2014, ISIS claimed to execute 1,700 Shi'ite members of the Army attempting to flee the militants. Soldiers were shot execution style and blood was left visible on the cement, before being tossed into mass graves.
According to an Iraqi official, eleven bodies from the execution have been recovered downstream in the Tigris River.
"Another piece of this gruesome puzzle has come into place, with many more executions now confirmed," said Peter Bouckaert of Human Rights Watch. "The barbarity of the Islamic State violates the law and grossly offends the conscience."
Some of the imagery published shows large groups of men in shallow trenches being executed while their hands were tied. Executions took place next to Tikrit's presidential palace compound, formally a residence of Iraqi President Saddam Hussein.
ISIS initially told the men, many who had changed into civilian clothes to avoid capture, that they would be returned home safely. Instead, they were marched into lines, robbed of their possessions and executed.
Human Rights Watch expects the full death toll to climb from the massacres as new evidence emerges and is analyzed by experts.
Last week ISIS released a video purportedly showing mass executions of dozens of men in the Roman ruins of Palmyra, Syria, an ancient city they overran in May.
Part of ISIS tactics include using mass executions to terrorize the local populace as well as making propoganda videos from them to recruit more fighters, including some from the Western world.
On Thursday, Iraqi forces were able to repel attacks from ISIS in Iraq's Al-Anbar Provence. The Iraqi military has struggled to reclaim lost ground against ISIS.
Previously referring to ISIS as "jayvee," Obama declared this month that the battle against them "is a long term campaign."