The historian lives for the revelatory document. He spends long days in the libraries and the archives, turning pages, poring over routine correspondence, in the hope of striking golden words - a single magical page that, as he turns it, unveils the elusive past. I have found at least one such document for every book I have written. And I still remember each one with almost photographic clarity.
The account book that showed just how much the Rothschilds had lent the Austrian chancellor Prince Metternich. The diary of the ordinary Tommy who had quite enjoyed killing Germans on the Western Front. The letter that revealed that John Maynard Keynes had been in love with one of the German delegates to the Versailles conference. The explicit order to direct the efforts of Bomber Command at German civilians. Each one provided a flash of illumination, confirming or refuting an earlier hypothesis. My pulse quickened as I read and reread them.
I had something of that same excitement as I read the Verbatim Transcript of Combatant Status Review Tribunal Hearing for ISN 10024, otherwise known as Khalid Sheikh Mohammed, the al-Qaeda leader captured in Pakistan in 2003. For this document, released by the Pentagon last week, tells us more about the true nature of the war on terror than any other single document I have read. In particular, it shows us how the combatants in this war are in subtle ways growing alike.
"There's an osmosis in war," declares the fascistically inclined American general in Norman Mailer's Second World War novel The Naked and the Dead, "Call it what you will, but the victors always tend to assume the... the, eh, trappings of the loser."
"As kinetic energy," he explains to Mailer's doomed hero, "a country is organisation, co-ordinated effort... fascism... The purpose of this war is to translate America's potential into kinetic energy... America is going to absorb that dream, it's in the -business of doing that now." It was precisely that fascist contamination which after the war produced McCarthyism and reinvigorated racism in the South.
Now we can see the process of contamination at work again - though in this case, intriguingly, it is a process of mutual contamination.
What is obviously sensational about Khalid Sheikh Mohammed's statement before the tribunal is the sheer scale of the terrorist campaign he claims to have masterminded.
As Osama bin Laden's "Military Operational Commander", he was responsible not only for "the organising, planning, follow-up and execution... from A to Z" of the terrorist attacks of September 11, 2001, but also for the 1993 attempt to blow up the World Trade Centre, the murder of the American journalist Daniel Pearl, the attempt by the shoe bomber Richard Reid to blow up a plane, the murder of two US soldiers in Kuwait, and other bombings in Bali, Mombassa and Turkey.
Moreover, his confession to the tribunal alluded to more than 20 terrorist crimes which he planned but did not succeed in carrying out, including "Dirty Bomb Operations on American soil", post-9/11 "Second Wave" attacks on the Library Tower in Los Angeles, the Sears Tower in Chicago, the Plaza Bank in Washington state and the Empire State Building in New York, and further attacks on New York's suspension bridges and stock exchange; on American nuclear power plants; on Heathrow airport, Canary Wharf and Big Ben; on the Straits of Hormuz and Gibraltar, on Singapore and the Panama Canal; on Nato's headquarters in Brussels; on three American embassies; on Israel itself and four Israeli embassies; and on Western targets in Thailand and South Korea.
As if that were not enough, Mohammed informed the tribunal that he was responsible for planning the assassinations of former Presidents Jimmy Carter and Bill Clinton, Pope John Paul II and the Pakistani President Pervez Musharraf.
Oh, and he also intended to destroy "an American oil company owned by the Jewish former Secretary of State, Henry Kissinger, on the Island of Sumatra".
So breathtaking and, in certain respects, bizarre is the list of alleged targets that it is tempting to wonder if the prisoner was in fact making mock of his military audience. Yet the al-Qaeda attacks that were actually carried out were scarcely less breathtaking and bizarre.
If even a quarter of these other atrocities have been prevented by this man's detention and other measures taken by the Bush administration, this President deserves eternal fame, not the opprobrium that is currently being heaped upon him.
Yet the transcript also sheds light on the dark underbelly of Mr Bush's presidency. "Did you make these statements because of the treatment you received from these... interrogators?" the "detainee" is asked by the president of the tribunal.
"You are not under any pressure or duress today," he later asks, "is that correct?"
"I know American people are torturing us from Seventies," Mohammed later declares. "I know they talking about human rights. And I know it is against American Constitution, against American laws." These words remind us that there is something rotten at the heart of this system of military justice.
Not only does the court president implicitly acknowledge that the prisoner before him has been tortured in the past. He also makes it clear that the prisoner is being denied proper legal representation; he has only a US Air Force lieutenant-colonel to act as his "personal representative".
Everyone in the courtroom except the prisoner and the translator is an American military officer. Mohammed's request for two fellow prisoners to be summoned as witnesses is denied. He is informed at the end of the hearing that he will almost certainly remain in captivity for an indefinite period.
And quite right too, you may well say, given the monstrous nature of the crimes and intended crimes to which he has confessed, and given his readiness to acknowledge that he is an enemy combatant at war with the United States - a "jackal fighting in the nights", in his own striking phrase.
But does it really honour the memory of Daniel Pearl to torture his murderer? And what of the other prisoners who, according to Mohammed, are being erroneously held in the same judicial limbo-land as himself: Afghans and Pakistanis who had nothing whatever to do with al-Qaeda?
Here we see Mailer's law of the osmosis of war at work: the indiscriminate terrorists who perpetrated 9/11 have elicited from the United States an equally indiscriminate response. The guilty and the innocent are thrown into military prisons. Military retaliation too has been indiscriminate, not least in Iraq.
There is, nevertheless, a twist in the tale. For the transcript also shows that the osmosis of this war is a reciprocal process.
Consider what it reveals about al-Qaeda as an organization. It relied heavily on computers in preparing the 9/11 attacks. It has learned from Western warfare the importance of economic targets. It regards the manipulation of the media as an integral part of its terrorist mission. Its leaders speak English.
And - most fascinating of all - its Military Operational Commander claims the greatest of the Founding Fathers as his role model. I quote: "If now we were living in the Revolutionary War and George Washington he being arrested through Britain. For sure... they would consider him enemy combatant."
You can imagine the assembled soldiery rolling their eyes heavenwards. An Islamist Washington fighting for liberty against American redcoats? What could be more preposterous? Except that this reveals another characteristic of the osmosis of war. Pace Mailer, it is far from obvious to the two sides in this war that they are growing subtly alike.
Only in retrospect, as the historian leafs through this and the other documents that survive "redaction" and classification, will it become apparent to Americans how the war on terror turned a part of them into their enemy - and a part of their enemy into themselves.