(Sky News) 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.
ISIS 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.