Rachel Cooke meets the most-feared investigative reporter in Washington

How does Hersh operate? The same way as he's always done: it's all down to contacts. Unlike Bob Woodward, however, whose recent books about Iraq have involved long and somewhat pally chats with the President, Hersh gets his stuff from lower down the food chain. Woodward was one of those who was convinced that WMD would be found in Iraq. 'He does report top dollar,' says Hersh. 'I don't go to the top because I think it's sorta useless. I see people at six o'clock in the morning somewhere, unofficially.' Are they mostly people he has known for a long time? 'No, I do pick up new people.' But with new contacts he must be wary; there is always the danger of a plant. His critics point to what they regard as his excessive use of unnamed sources. Others accuse him of getting things wrong and of being gullible. A low point came in the Nineties, when he embarked on a book about Kennedy, The Dark Side of Camelot. Hersh was shown documents that alleged the President was being blackmailed by Marilyn Monroe, and though he discovered that they were fake in time to remove all mention of them from his book, the damage to his reputation had already been done - and the critics let rip anyway, for his excitable portrayal of JFK as a sex addict and bigamist. There was also the time, in 1974, when he accused the US ambassador to Chile, Edward Korry, of being in on a CIA plot to overthrow President Allende. Some years later, Hersh had to write a long correction; it ran on page one of the New York Times. As a Jew, his mailbag since 9/11 has also included letters from readers who denounce him as a self-hater (later, at this office, he shows me one of these: its author, an MD with a Florida postcode, accuses him of being a 'kapo' - the kapo were concentration camp prisoners who worked for the Nazis in exchange for meagre privileges).

American investigative journalist Seymour Hersh. Photograph: Martha Camarillo