(The Telegraph newspaper) The Khasfa sinkhole was once an inconspicuous feature in the barren desert just off the Baghdad-Mosul highway.
Now, this natural depression five miles outside Mosul is believed to be the biggest mass grave in Iraq.
ISIS killed and dumped the bodies of thousands of security personnel here after they captured the city in 2014, according to local villagers, Iraqi police and human rights organisations.
Most victims were shot and dumped into the pit, witnesses said, while others perished in vehicles driven over the edge of the pit.
“Daesh would drive the victims to Khasfa in convoys of minibuses, trucks and pick ups. The men had their hands bound and their eyes blindfolded.
“They were taken to the sinkhole and shot in the back of the head,” said Mahmoud, a 40-year-old from the nearby village of Sananik who declined to give his full name for security reasons.
The dead would either tumble into the hole after being shot or be tossed into it by their masked killers, he said.
The Daily Telegraph was able to visit the Khasfa site this week after Iraqi security forces fighting to recapture the western half of Mosul took control of the area.
On Friday Iraqi fighters recaptured the city’s airport from Isil, as they pushed into the densely-populated western sector.
Iraqi fighter jets also dropped bombs on Isil positions inside Syria yesterday, the first time the Iraqi government has publicly acknowledged striking militant targets inside Syria.
Isil is believed to have embarked on a campaign of extermination in Mosul, hunting down and killing policemen and soldiers and burying them in mass graves in the surrounding desert, which is pockmarked with sinkholes and natural crevices.
A grave containing the bodies of at least 300 members of the security forces was discovered last November on the outskirts of Hamman al Alil, a town about 30 kilometres from Mosul.
But the scale of the killing at Khasfa dwarfs all other known sites. “Khasfa is definitely one of the biggest, if not the biggest, mass grave by Isil in Iraq.
And from what we have heard it is not just a grave but also an execution site,” said Belkis Wille, senior Iraq researcher for Human Rights Watch. The organisation estimates that around 4,000 bodies are buried at the site.
Locals said the sinkhole was more than 400 metres deep before the dead began piling up.
The body count at Khasfa outstrips the most infamous massacre committed by Isil – the murder of army cadets at the Camp Speicher military base near Tikrit.
Isil militants butchered as many as 1,700 Shia recruits in the June 2014 massacre, turning the water of the Tigris red with blood.
At Khasfa, 2,000 policemen and soldiers were murdered in one day alone, claimed Mahmoud, who said he was forced to watch mass executions by the jihadists on four separate occasions.
“In the beginning, you couldn’t see the corpses at the bottom of the hole. Only later, when it began to fill up could you see the bodies,” he said.
The victims of one of the executions he was forced to watch included his cousin, who worked as a police office, he said.