There have been many horrendous propaganda videos produced by Islamic State, but the latest I have seen is genuinely the worst.
It shows young boys being trained to fight and let loose in a disused warehouse.
Dressed in black combat fatigues and masked, the boys run through military drills. It is standard propaganda stuff. Every terror organisation films this type of thing.
But there is a difference.
On the highly produced film, you see handcuffed men running from room to room. They are being hunted. It is utterly awful when you realise it is real. This looks like a Hollywood film. But it is actually happening.
As they hunt down the men, they kill them. The final moments of fear, screaming, begging and the pain are glorified. It is astoundingly barbaric.
The video is important because it explains why these are not just errant youths. They have been brainwashed, and they are deadly.
The question is whether or not they always will be – because in the chaos of the Mosul battle many of them are on the loose.
Sky News has been given extremely rare access to a detention centre in Erbil. Here, they hold the boys who have been caught – as well as suspects.
Some were identified in the sprawling refugee camps dotted across northern Iraq and turned in.
A dozen or so share a cell. They are well treated and spend their time praying and trying to learn to read. One boy studiously used an English dictionary as we filmed.
Their stories are very similar. Initially reluctant to join Islamic State, they are groomed by IS members to take up the challenge of Jihad and, ultimately, martyrdom.
Mahmoud would talk to us. He is 12. He admits to being a member. His grooming took six to seven months.
My friend came to me. He showed me photos, he told me: ‘Come with me, we will give you a weapon, a car, a wife. Come with us, you will have virgins in paradise.’
They brainwashed me and took me, Mahmoud told us in his cell.
They were showing us on TV how a suicide bomber goes and explodes himself. How booby-traps were exploded. How weapons were dismantled. How you can hit an armoured vehicle. Where to shoot on the windshield of a hummer to hit it and break it, which angle to shoot. How you can sneak and attack them secretly. How you go and bring back injured ones. These things, he explained.
He says he was terrified at what he was seeing and hearing. He wanted to quit. So he was punished.
They put me in prison with no food or water – the most dreadful punishment. From sunrise to sunset, you get one loaf and one bottle of water. Then another small bottle of water until the next day, and sometimes they don’t bring you anything.
On Friday is nothing. They bring dirty rice and sauce to punish you. And they bring a scholar. He will decide if you go back to them or quit.
Next they whip you and torture you but I withstood all the torture and then I quit, Mahmoud said.
For the families of this lost generation, these are difficult times.
They come to meet their children aware that they could be sentenced to 15 years or longer in prison. The families themselves could be ostracised in the days after IS has gone.
Their meetings are short and not very private, but the Kurdish authorities holding them will take no chances with the terror threat.
Of the 236 inmates held here, 215 are suspected of terrorism and there are camps near by overflowing with young men whose intentions are unknown.
The curse of Islamic State’s hate-filled messages and doctrine of pure evil could take at least a generation to pass.