There is a scratchy patch of land south of Mosul that is dotted with dozens of burnt-out oil tanks and bits of scorched grass.

The men from so-called Islamic State used this spot to refine petrol in what was a great do-it-yourself fuel distillery.

But they also had another purpose for this place - mass murder.

Some 200 metres off the main track, there is a cavernous hole in the earth that locals call "the Khasfa" - a circular sinkhole carved from porous rock with water flowing through the bottom.

IS turned the crater's rim into an execution site and threw their victims down the hole - and these acts of depravity were committed so frequently that the Khasfa is almost certainly the biggest mass grave in Iraq.


It is for that reason that Fawaz Abdelabbas, the deputy head of the International Commission for Missing Persons in Iraq, is determined to survey the site as quickly as possible - and we found him and other members of his Baghdad-based delegation on a dirt track some 300 odd metres from the hole.

"This is the way," said the urbane director. "Now we try to find to get to the sinkhole. Murphy, what do you think?"

But there was a serious problem - IS has saturated this wasteland with land-mines.

:: Traumatised children of Mosul

Mosul refugee camps at capacity

Sky News understands that five people had lost their lives trying to get there, including Kurdish journalist Shifa Gardi, who trod on an explosive device four weeks ago.

Unsurprisingly then, Mr Abdelabbas's mission was about to come grinding to a halt.

He said: "We agreed with the Iraqi government that they would have the forces to support us with a de-mining team because we are told the route (to the hole) is full with mines and…. let's discuss the matter with the police chief."

But the district police chief was shuffling uncomfortably from side-to-side. He did not have a de-mining team.

The delegation was stuck.

"Is it frustrating?" I asked the commission's deputy head. "Of course," he replied. "But this is the reality of Iraq."

Image: The sinkhole is rumoured to contain thousands of bodies

We put a drone in the air and flew it over the hole, although high winds made it difficult to control.

Nonetheless, we saw that IS had tried to fill it in with earth - a giant construction project, recently confirmed by satellite photographs.

Still, one section has begun to slip and we noticed what looked like several vehicles lying at the bottom.

:: The battle for Mosul: A timeline

That came as little surprise to Mohamed Abdelkarim, who is head of a nearby village.

He regularly witnessed prisoners crammed in trucks and buses being taken to the hole. Other witnesses report seeing vehicles (and their passengers) being physically pushed into the Khasfa.

"How many bodies are in there?" I asked him.

"We think 6,000, maybe more," said the village chief. "The population of Mosul is 3 million, plus other villages and towns in Salahaddin Province. Any public servants, policemen, military officers, doctors, scientists (were thrown in the hole)."

Getting to the hole and investigating Islamic State's crimes will be a colossal task - a job that will stretch the capabilities of this fragile, war-weary nation.

But Mr Abdelabbas says it is essential. "We want to exhume the bodies and begin the process of identification and we will do it according to international standards," he told me confidently.

On the frontline in Mosul

"Returning the remains to grieving families will help them deal with the past but it will also demonstrate that the (Iraqi) government actually cares and respects them.

"This is about reconciliation."