Four planes. Nineteen hijackers. Three thousand dead. Ten years on, what are we to make of 9/11? One-off atrocity? Or historical watershed? Act of terrorism – or The Day the World Changed?

What about the reaction to 9/11? Afghanistan. Bali. Iraq. Madrid. London. Hundreds of thousands more dead. Summarising 9/11 and its aftermath, one is reminded of the Peanuts cartoon in which the hapless Charlie Brown faces the exam question: ‘Explain World War II (use both sides of the page, if necessary)’.

Eight months ago, following 4 years’ research, I thought I had pretty much knocked this subject on the head. I’d interviewed hundreds of policymakers, been to Iraq, come to a few conclusions; delivered a manuscript on time (well, sort of). The book was out. It was over.

Then came the call. Al Jazeera wanted a documentary series. A big one.  I was summoned to London and introduced to a deceptively quiet, smartly-suited chap who turned out to be the Head of Programmes. We drank coffee. Then I went home. The next day some personnel-type in Qatar, whose name I still can’t pronounce, emailed me a contract to produce a three hour series. Someone was in a hurry.

For non-TV people, a catch-me-up: a three hour documentary series takes a long time to make. Probably the best part of a year. Al Jazeera wanted this one in four months. Clearly, it was going to be tight. But then, Al Jazeera is a news organisation, with experience of turning around breaking stories in a matter of minutes. The company probably knew what it was doing. I signed the contract, moved up to London and started research.

Then came The Discussion.

It happened in a cafe near Al Jazeera’s Knightsbridge offices, shortly after the death of Osama bin Laden. The Head of Programmes, for once, was in casual mode: wearing a short-sleeved shirt. He grabbed me by the arm and ushered me outside. The ensuing exchange went almost exactly like this:

Head of Programmes: (thoughtfully): Dominic, you know what we’re missing in this series?

Me: No. What are we missing?

HoP: Al Qaeda.

Me (with some trepidation): Aha…

HoP: I think we need them. You’ll have to arrange interviews.

Me (guarded now): Won’t al Qaeda be hard to find at the moment, after the death of bin Laden and all?

HoP: We’ve got three months till transmission, though, haven’t we?

I should perhaps add here. I had only had one interaction with al Qaeda up to this point. It was in Baghdad in 2008 and was so nerve-jangling that even my Iraqi fixer shortly afterwards changed his line of work.

How we eventually got al Qaeda to talk to us – and what, exactly, they said – is perhaps a subject for another time. But we did get some interviews. Six, in fact.

We used them sparsely, slotted amongst other individuals that we thought might help to put a human face to events since that fateful September day. Bin Laden’s next door neighbour in Jalalabad (Osama never attended parties, apparently); the CIA officers who captured al Qaeda logistics chief, Abu Zubaydah, in Pakistan in 2002 (Zubaydah had accidentally been shot three times: ‘we had to keep him alive’ recalled one ‘so we could interrogate him’.)

The interviews came slowly at first, then in a glut. The Danish artist responsible for the bomb/turban cartoon whose publication led to rioting and two hundred deaths in 2006; the guards at the al Askari shrine in Samarra, Iraq – whose bombing the same year kick-started the civil war. The al Jazeera journalist incarcerated in Guantanamo Bay for 6 years while US intelligence tried to persuade him to spy for them against the news organisation.

Others were less well-known. The Afghan boatman who ferried bin Laden away from Tora Bora in 2001. The American soldier who plucked a fatally wounded Iraqi child from the back of a minivan his colleagues had just attacked – and ran him to safety. The Palestinian-born journalist who took bin Laden to one side in 1996 and suggested that single-handedly declaring war on the United States was perhaps not such a wise idea.

So now the series is finished. What emerges? What are we to make of the 9/11 Decade? For me, the overriding impressions: chaos. Destruction. And, above all, casualties. In Iraq, in Afghanistan, in Jordan. Spain, London. And, of course, in New York and Washington.

It’s an old cliché that those who do not learn their history are condemned to repeat it. Hopefully we have learned something from the last ten, bloody, years. Let’s hope the next ten are a bit better.