Six months ago - on May 16 - The Jerusalem Post featured a report about our book Foxbats over Dimona: The Soviets' Nuclear Gamble in the Six-Day War. Our book challenged the almost universal consensus on the origins and conduct of the conflict that has shaped the Middle East ever since. We demonstrated that the crisis and war of May-June 1967 were deliberately instigated by the USSR, which jointly with Egypt and Syria planned to provoke Israel into a first strike. This would brand Israel as the aggressor and legitimize a direct Soviet military intervention to assist an Arab counterattack. One of the Kremlin's main motives, and a factor that determined the timing, was the Soviets' intent to prevent Israel from attaining nuclear weapons. In that Post report, historian Michael Oren became the first of several critics who disparaged our thesis on the grounds that they (or we) had not found "any documentary evidence to support" the book's central claims - although Oren admitted that he had visited the Soviet archives and "not a lot has been declassified." The Post report was widely (though often inaccurately) reproduced in the Russian media and Internet, arousing some heated debate - and stimulating the emergence of numerous new testimonies. In the overwhelming majority of cases, they confirmed the picture we had assembled. Some of this new evidence was presented in another feature in the Post (on August 23). But the renewed discussion has also revealed information that pertains directly to general questions of historical research methodology. It bore out our argument that by insisting on archival documents alone as the touchstone of factual truth, historians can become accomplices in the concealment of the actual events - instead of facilitating their exposure. THE MOST dramatic instance is an article in the Russian weekly VPK by a retired KGB colonel, Boris Syromyatnikov, entitled "The Six-Day War Might Not Have Occurred: If the Soviet General Staff Had Heeded the Arguments of a Military Intelligence Operative." The former counterintelligence officer relates that in "early 1967," he submitted a lone dissenting opinion as to the results of the already-anticipated war: he estimated that the Arabs would lose. It was shelved as heretical. In November 2000, the retired Syromyatnikov attempted to retrieve his memorandum. "But I received a letter from the FSB [KGB successor agency] Central Archive, stating: 'Unfortunately, the document in which you are interested is not â€¦held at the Russian FSB Central Archive. For your information, a number of files from 1967â€¦ were destroyed in 1978.' That is how the state security agencies treated their own history." In Foxbats, numerous participants of the abortive Soviet intervention spoke of orders that they had received only orally; at the leadership level, note-taking was forbidden at Politburo sessions. Even president Mikhail Gorbachev, less than a decade after the USSR invaded Afghanistan, could not find any written resolution to do so. We also showed how official documents often were designed - with their possible future release in mind - to distort the facts rather than to reflect them. Now the FSB's response to its own former officer provides the first direct and official confirmation by a Russian state agency that entire categories of documents, to the extent that they were ever promulgated and might offer valid insights, do not merely remain classified but no longer exist. In fairness, it must be stressed that the suppression of archival evidence is not an exclusively Soviet or Russian practice. Our book cites several examples in which the United States and Israel have also blacked out matters that their governments preferred to conceal - including Soviet-related aspects of the Six-Day War. Indeed, only last month - in a different context - it was Russian President Vladimir Putin who, by posthumously decorating a Soviet spy for penetrating the Manhattan Project, first exposed a major nuclear espionage case which the United States had covered up for more than 60 years. Historians are thus faced with the choice whether to countenance such Orwellian effacement of past events by tossing the records down the "memory hole" - or to utilize, as we did, a wide variety of alternative sources in order to piece together the actual facts as they took place: what the Soviets and others did, rather than what they declared or put in writing. This meant tracking down, cross-checking and verifying myriad memoirs, publications, and sometimes even official documents that slipped through security filters with inadvertently revealing remarks. That is harder work than waiting for archives to be systematically opened, and then relying on their neatly arranged boxes and files as exhaustive and authoritative. But it is essential if future generations are to know what actually happened, rather than what the interested parties preferred posterity, as well as their own contemporaries, to believe. The writers are based in Jerusalem.