Lying among a pile of papers at the hideout in Pakistan where Osama Bin Laden was shot dead was a carefully worded 21-page letter.
It warned of the rise of a new and ruthless group of Islamic extremists capable of such extreme brutality that al-Qaeda should sever all links with them.
In fact, it claimed the Islamic State of Iraq and Syria (or ISIS) had such complete disregard for civilian life that it could damage the reputation of al-Qaeda - if such a thing were possible for an organisation that has long traded in murderous terrorism.
The document, written by one of Bin Laden’s senior officials in 2011, went on to catalogue some of its acts of barbarism - including the use of chlorine gas as a chemical weapon, bombing mosques and a massacre in a Catholic church in Baghdad.
In essence, the letter said that ISIS was simply too extreme even for the group that killed thousands in the Twin Towers on September 11, 2001.
Today, ISIS, which now styles itself as simply Islamic State (IS), has become a powerful military force that has control of an area larger than Great Britain.
Living under their ultra-conservative interpretation of Islam are six million people, a population larger than that of Ireland, Denmark or Finland.
Their trademark black jihadi flag has fluttered in the background of chilling “promotional” videos of executions - including crucifixions and beheadings - as the militia seizes vast areas of Iraq and Syria. In short, the “caliphate” - or Islamic state - it claims to have established represents the biggest shift in the political geography of the Middle East since the borders of modern Iraq and Syria were drawn under the Sykes-Picot agreement drafted between Britain and France in 1916.
To understand the threat Islamic State poses to the region, it first needs to be appreciated how it has grown into a force to rival al-Qaeda.
The group was founded by 43-year-old Abu Bakr al Baghdadi, a firebrand cleric held prisoner for four years by American troops in Iraq.
The leader, a Sunni Muslim who despises the Shia-run Iraqi government, now commands more than 10 000 fighters, many of them former Saddam Hussein-era soldiers or disenchanted Sunnis who lost power and influence after the fall of the dictator’s regime.
More worryingly, foreign Islamic extremists, including about 500 Britons, have joined IS to fight in Syria and Iraq.
The group controls valuable oil fields and, with the help of wealthy Sunni backers from the Gulf states, is estimated to have amassed a staggering £1.2 billion. It has even sold 8 000-year-old antiquities it has seized.
But its real assets lie in the fanatical loyalty of its fighters (they all swear allegiance to IS) and the state-of-the-art weaponry they now possess.
Much of its armoury was seized during a lightning advance several weeks ago, when fleeing Iraqi troops abandoned the artillery and armoured vehicles that it had been given by US forces.
With captured American Humvees and the latest precision firepower, they are more than a match for the formidable Kurdish Peshmerga - which defends the Kurds’ semi-autonomous region in the north - and its 12.7mm Soviet-era machine-guns and outdated Russian T-55 tanks.
As Ali Khedery, a former American official who advised US generals in Iraq, has said: “They are literally outgunned by an IS that is fighting with hundreds of millions of dollars of US military equipment seized from the Iraqi Army, which abandoned it.”
So it would be naive in the extreme to think of Islamic State as a motley crew of scrappers.
A force capable of meting out so much wanton violence is invariably led by commanders who rule with an iron will.
But what marks them out as being particularly savvy is the way they have used social networking sites like Twitter and Facebook to create a digital “public relations” machine to promote their jihad and strike fear into the hearts of their enemies.
Any fighter on the ground can film an act of brutality and upload the footage in a matter of minutes - although some videos of botched amputations or killings has led to a clampdown by IS commanders. One Spanish fighter promised to upload a film of a man being crucified for his friends back home, but was quickly reprimanded by his superiors.
His later contrite posting simply read, “Our leadership forbade anyone filming it.”
However, the videos already in circulation have already created a climate of terror.
Some opposition soldiers, particularly in Syria, are defecting to the group. After all, IS has money - some of which is said to have come through private donations from Saudi Arabia and Qatar.
Equally, those captured by the militia face a stark choice - defect or die.
Despite being trained by American troops, the Iraqi army has proven worryingly ineffective in taking on this threat.
It’s why the terrorists now control much of the north of the country. They have also seized a former chemical weapons plant and a large dam that could be blown up to flood the regions downstream.
The populations of the Kurdish capital of Irbil, as well as the national capital Baghdad, are now in no doubt as to the fate that would befall them if these Sunni extremists prevail.
If IS cannot be stopped, they are clinging to the hope that rescue will come in the form of Iran, which supports Iraq’s Shia-led government, or the US.
However, both countries are reluctant to commit troops on the ground in the political and religious quagmire of Iraq.
Abu Bakr al Baghdadi knows this only too well.
It’s is why his IS troops have been so emboldened to sweep across much of Syria and northern Iraq in recent weeks. In the past fortnight they have fought on five fronts: against the Iraqi army, the Kurdish peshmerga, Bashar Al-Assad’s Syrian regime, the Syrian opposition and the Lebanese army.
When he was released by the American military police from the Camp Bucca detention facility in Umm Qasr, where he was held as an insurgent, al Baghdadi said ominously: “I will see you guys in New York.”
A fanciful threat?
Perhaps not, when you consider that the greatest threat Islamic State poses to the world is that this so-called caliphate becomes a training ground for international terrorism, and unleashes an army of extremists against the West to kill and maim far from the bloodsoaked deserts of Iraq. - Daily Mail