1. The leaders of ISIS are much smarter than I realized. 

2. The leaders of ISIS are well known to America:

The small militant group that Baghdadi headed was one of dozens that sprouted from a broad Sunni revolt – many of which would soon come together under the flag of al-Qaida in Iraq, and then the Islamic State of Iraq. These were the precursors to the juggernaut now known simply as the Islamic State, which has, under Bagdhadi’s command, overrun much of the west and centre of the country and eastern Syria, and drawn the US military back to a deeply destabilised region less than three years after it left vowing never to return.

But at the time of his stay at Bucca, Baghdadi’s group was little-known, and he was a far less significant figure than the insurgency’s notional leader, the merciless Abu Musab al-Zarqawi, who came to represent the sum of all fears for many in Iraq, Europe and the US. Baghdadi, however, had a unique way to distinguish himself from the other aspiring leaders inside Bucca and outside on Iraq’s savage streets: a pedigree that allowed him to claim direct lineage to the Prophet Muhammed. He had also obtained a PhD in Islamic studies from the Islamic University of Baghdad, and would draw on both to legitimise his unprecedented claim to anoint himself caliph of the Islamic world in July 2014, which realised a sense of destiny evident in the prison yard a decade earlier.

“Baghdadi was a quiet person,” said Abu Ahmed. “He has a charisma. You could feel that he was someone important. But there were others who were more important. I honestly did not think he would get this far.”

Baghdadi also seemed to have a way with his captors. According to Abu Ahmed, and two other men who were jailed at Bucca in 2004, the Americans saw him as a fixer who could solve fractious disputes between competing factions and keep the camp quiet.

“But as time went on, every time there was a problem in the camp, he was at the centre of it,” Abu Ahmed recalled. “He wanted to be the head of the prison – and when I look back now, he was using a policy of conquer and divide to get what he wanted, which was status. And it worked.” By December 2004, Baghdadi was deemed by his jailers to pose no further risk and his release was authorised.

“He was respected very much by the US army,” Abu Ahmed said. “If he wanted to visit people in another camp he could, but we couldn’t. And all the while, a new strategy, which he was leading, was rising under their noses, and that was to build the Islamic State. If there was no American prison in Iraq, there would be no IS now. Bucca was a factory. It made us all. It built our ideology.”

As Isis has rampaged through the region, it has been led by men who spent time in US detention centres during the American occupation of Iraq – in addition to Bucca, the US also ran Camp Cropper, near Baghdad airport, and, for an ill-fated 18 months early in the war, Abu Ghraib prison on the capital’s western outskirts. Many of those released from these prisons – and indeed, several senior American officers who ran detention operations – have admitted that the prisons had an incendiary effect on the insurgency.

“I went to plenty of meetings where guys would come through and tell us how well it was all going,” said Ali Khedery, a special aide to all US ambassadors who served in Iraq from 2003-11, and to three US military commanders. But eventually even top American officers came to believe they had “actually become radicalising elements. They were counterproductive in many ways. They were being used to plan and organise, to appoint leaders and launch operations.”

We wrote each other’s details on the elastic of our boxer shorts. When we got out, we called each other Abu Ahmed agreed. “In prison, all of the princes were meeting regularly. We became very close to those we were jailed with. We knew their capabilities. We knew what they could and couldn’t do, how to use them for whatever reason. The most important people in Bucca were those who had been close to Zarqawi. He was recognised in 2004 as being the leader of the jihad.

“We had so much time to sit and plan,” he continued. “It was the perfect environment. We all agreed to get together when we got out. The way to reconnect was easy. We wrote each other’s details on the elastic of our boxer shorts. When we got out, we called. Everyone who was important to me was written on white elastic. I had their phone numbers, their villages. By 2009, many of us were back doing what we did before we were caught. But this time we were doing it better.”

According to Hisham al-Hashimi, the Baghdad-based analyst, the Iraqi government estimates that 17 of the 25 most important Islamic State leaders running the war in Iraq and Syria spent time in US prisons between 2004 and 2011. Some were transferred from American custody to Iraqi prisons, where a series of jailbreaks in the last several years allowed many senior leaders to escape and rejoin the insurgent ranks.

Abu Ghraib was the scene of the biggest – and most damaging – breakout in 2013, with up to 500 inmates, many of them senior jihadists handed over by the departing US military, fleeing in July of that year after the prison was stormed by Islamic State forces, who launched a simultaneous, and equally successful, raid on nearby Taji prison.

Iraq’s government closed Abu Ghraib in April 2014 and it now stands empty, 15 miles from Baghdad’s western outskirts, near the frontline between Isis and Iraq’s security forces, who seem perennially under-prepared as they stare into the heat haze shimmering over the highway that leads towards the badlands of Falluja and Ramadi.

Parts of both cities have become a no-go zone for Iraq’s beleaguered troops, who have been battered and humiliated by Isis, a group of marauders unparalleled in Mesopotamia since the time of the Mongols. When I visited the abandoned prison late this summer, a group of disinterested Iraqi forces sat at a checkpoint on the main road to Baghdad, eating watermelon as the distant rumble of shellfire sounded in the distance. The imposing walls of Abu Ghraib were behind them, and their jihadist enemies were staked out further down the road.

The revelation of abuses at Abu Ghraib had a radicalising effect on many Iraqis, who saw the purported civility of American occupation as little improvement on the tyranny of Saddam. While Bucca had few abuse complaints prior to its closure in 2009, it was seen by Iraqis as a potent symbol of an unjust policy, which swept up husbands, fathers, and sons – some of them non-combatants – in regular neighbourhood raids, and sent them away to prison for months or years.