Hersh even says that it was General Martin Dempsey, the chairman of the US Joint Chiefs of Staff, who told President Barack Obama just days before the American strikes on Syria were due to start that the evidence was not strong enough to justify an American attack on the Syrian regime.
The rest of the story we already know. Obama postponed the attack by deciding, quite suddenly, that he had to get Congressional support for it. Then he cancelled it entirely once the Russians gave him the face-saving alternative of getting Assad to hand over all of his chemical weapons for destruction. There is no chance of an American attack on Syria now. But could Hersh's back-story be true?
Not one American paper or magazine was willing to print Hersh's story, so it was finally published in the most recent issue of the London Review of Books. The US media are still studiously ignoring the story, and the Turkish government and various branches of the US government have naturally all issued indignant denials. But the official story never made any sense at all.
By last August it was clear that Assad's regime would eventually win the civil war unless there was some radical change in the situation (like an American bombing campaign against it). So Assad's survival depended on not giving the United States any reason to attack him.
Barack Obama had already said that any use of poison gas by the Syrian regime would cross a "red line" and trigger an American attack.
In mid-August there were United Nations inspectors in Damascus to look into two much smaller attacks earlier in 2013 that seemed to involve poison gas. And we are asked to believe that at that precise moment Assad thought it would be a neat idea to kill one or 2000 innocent civilians in the city with poison gas.
So who did it? The obvious question to ask was: Who stands to benefit from this attack? - and the answer was certainly not Assad. He would not have done this unless he was very stupid, and being wicked does not make you stupid. Whereas the rebels had every reason to do it, in order to suck American firepower in on their side.
But I must admit that it felt very lonely making this argument at the time. I had no evidence that al-Nusra, or any other rebel group, had carried out the attack. I just said that motives matter, and that Assad had no plausible motive for doing it. And of course I couldn't say where the rebels would have got their chemical weapons from, if they did it. Hersh says: the Turks.
Recep Tayyip Erdogan, Turkey's prime minister for the past 11 years, has backed the Islamist rebels in the Syrian civil war from the start, and he will be in deep trouble if they lose. They WILL lose, unless either Turkey or the United States comes to their aid militarily. Erdogan would obviously rather have the US Air force do it rather than his own armed forces. So he had a good motive for giving the rebels the poison gas.
Hersh says that he has been told by a former senior official in the US Defense Intelligence Agency that that is what happened. You can read the details on the website of the London Review of Books. And yes, he's old, but that just means he has been getting it right about a lot of different things for a long time.
He's just a freelancer, but that's why people with a whistle to blow trust him to get the story out. And no, he hasn't got confirmation from three separate named sources. That's not how whistle-blowing works. But he is Seymour Hersh, and I strongly suspect that he is right.
Gwynne Dyer is an independent journalist whose articles are published in 45 countries.
