Mass graves, missing children: Evidence of brutality in Iraqi town of Sinjar

Sinjar is yielding up its secrets -- the whispers of those who prayed as they were killed. Grief for those captured and never seen again.

Mahama al-Shangali is the mayor of this town of fewer than 90,000 people in northern Iraq, in the heart of Yazidi country.

When ISIS swept through the Yazidi homeland, it was along the road into Sinjar that men, women and children who had been rounded up from the surrounding villages were driven.

Evidence of a massacre

As the mayor walks us to the other side of the heaped earth defenses that encircle the town, he tells us this was the site of an ISIS massacre.

This is where they buried the young men, the women and the boys -- children, really -- who refused to accompany ISIS. Who refused to be conscripted by the terrorist group as child soldiers.

Witnesses tell CNN that the victims in in these graves, more than 130 of them, had been selected to be taken to the nearby ISIS-controlled town of Tal Afar.

But they refused to go. So they were killed, young and old alike.

The importance of Sinjar in the fight against ISIS 00:55

Standing at the gravesite, I could still see tossed on the ground the cloth ties that bound their hands. The prayer beads they clutched until the end.

And I saw the empty bullet casings spit out by the guns fired by their killers.

Some Yazidis living in camps

From there we moved to a refugee camp, one of the many that now dot northern Iraq. Those who managed to flee ISIS have found refuge here.

Kurdish authorities tell CNN they have evidence that about 600 children were abducted from Sinjar and the surrounding Yazidi villages.

Around 200 have since escaped and are sheltering in camps like this one across the Kurdish region.

The Yazidis are linked to the ancient religions of this region. They believe in a single deity and a world ruled by seven angels, chief among them Melek Taus, the Peacock Angel.

ISIS considers the Yazidis to be devil-worshippers and wants to eliminate them. Killing and forced conversion of the Yazidis are espoused by ISIS as religious duties.

A hope to identify the dead

"At night, when the planes came, that was when it was scariest. In the dark, we would huddle together. All us boys just holding on to each other."

None of them dared cry, though, he says, terrified of the beatings that would bring from their captors.

The day they managed to escape was the first time Assim allowed himself to cry. That was the day he finally saw his mother again.

Back at the outskirts of Sinjar, in the near distance, we can see smoke rising from a mortar strike into an ISIS encampment.

Mass graves honeycomb the valley leading to the boundary of their territory. On the ground, the mayor spots a fragment of what appears to be a child's skull. Delicately -- reverently -- he places it on top of the grave.

One day, he tells us, he hopes it will be safe enough here for forensic investigators to come and identify the children who lie beneath this this rubble.