The conversation was typical. I was chatting to a producer at a leading American TV show last summer, trying to interest him in the CIA's programme of "extraordinary rendition", the transfer of terror suspects to countries such as Egypt and Syria. "I hear what you're saying. I realise these guys may be tortured," he said. "But how can we prove these people are innocent? That's what will interest our people."
My thoughts strayed. If I was talking about cannibalism, I wondered, would he be asking: "Can you prove that eating human flesh is unhealthy?" Surely there must be some things that are just plain wrong. Even on US network television.
I thought about that exchange, and others like it, a couple of weeks ago as I sat in a cafe in Johannesburg watching my BlackBerry vibrating around the table in response to alerts about the latest of hundreds of news stories about rendition. Eighteen months on, the world's media had finally woken up. What changed the story from one that few editors would touch to one making headlines across the world? The answer is, a vast amount of journalistic legwork. Not only have a good number of reporters dug and dug at the story, but they have co-operated, even those that are rivals, one turning up a new piece of information that spurred another to ask fresh questions.
And like much investigative journalism, it has hardly been glamorous: I spent much of the past year staring at spreadsheets of information about planes flying around the world and hunting for clues in obscure corners of the aviation world. Inevitably, family and friends said I was turning into a "plane-spotter". But the geeky work paid off: my colleagues and I found a way to track, briefly, a few of the CIA's most secretive operations.
It was soon after 11 September 2001, while I was conducting research in the US for the Sunday Times, that I first heard word of a programme that involved sending terrorist prisoners to foreign prisons or secret jails, without the need for awkward extradition hearings or legal process. There was a whole world out there, I heard, that was not illegal but "extra-legal", a term I found intriguing. At the time, just a handful of pioneering articles on the subject had been published, mainly in the US press.
Working as a freelance after the summer of 2003, I began to look at the subject in earnest. I travelled to Egypt to find out about the secret prisons involved and the fate of prisoners despatched to Cairo by the US. I met former CIA officials in Washington, DC and heard the story of Maher Arar, a Canadian sent by the US from JFK Airport to a torture cell in Damascus, Syria. When the Abu Ghraib scandal broke in April 2004, it seemed time to begin publishing. In an article for the New Statesman headlined "America's Gulag", I wrote of how the CIA had made use of a fleet of luxury aircraft, including Gulfstream jets, as well as military transport planes, to move prisoners around the world since 11 September 2001.
"Some of the prisoners have gone to Guantanamo, the US interrogation centre at its naval base in Cuba," I wrote. "Hundreds more have been transferred from one Middle Eastern or Asian country to another - countries where the prisoners can be more easily interrogated."
Coincidentally, the same week that article appeared (in May 2004) a Swedish TV team, led by the reporter Fredrik Laurin, broadcast the results of an investigation that traced the involvement of one US-registered Gulfstream - registration N379P - in the deportation of two Islamist terror suspects to Cairo from Stockholm. They had also spotted an article by a Pakistani journalist, Masood Anwar, who reported on the same plane's involvement back in October 2001 in the transfer of another suspect to Jordan. Was this plane, the Swedish journalists asked, operating undercover for the CIA?
Answers began emerging in November that year, by which time I had found a way to track the movements of that Gulfstream. I reported in the Sunday Times on at least 300 flights to 49 different destinations, including Guantanamo, Cairo, Kabul, Tashkent and Baghdad. What's more, these movements matched known CIA renditions.
Little by little the story unravelled. More cases of rendition have emerged. Most dramatic was the New York Times's revelation of the abduction of a German citizen, Khaled al-Masri, from Macedonia to Afghanistan; and then the revelation of a snatch operation in Milan, Italy, that has led to arrest warrants on kidnap charges for 22 suspected CIA agents allegedly involved.
At the beginning of 2005, former CIA and FBI officers intimately involved in the rendition programme confirmed to the New Yorker magazine that, contrary to what Condoleezza Rice has been telling European governments, officials were well aware that prisoners sent to countries such as Egypt would most likely be tortured. "Human rights is a very flexible concept," said Michael Scheuer, former head of the CIA's Osama Bin Laden unit, on the BBC's File on 4 radio programme.
Further investigations lasting many weeks, in co-operation with other journalists, made it possible to piece together the CIA's aviation operations, finding at least 26 planes owned by the agency and tracking hundreds of flights across the world. A New York Times reporter also found pilots who had worked for Aero Contractors, the main operating company for these CIA planes. One confirmed that the firm's job interviews took place at Langley, Virginia.
More accounts provided by detainees were cross-checked against this data: people such as Binyam Mohammed, the British resident now held at Guantanamo who described his 2002 journey from Pakistan to Morocco, where he spent 18 months in a secret prison and where guards, he claims, cut his body with a scalpel. The flight logs provided an exact match of his account.
But what has made the story so big in the past few weeks? That's a hard one. One important factor, of course, was a report in the Washington Post that described secret CIA jails in eastern Europe. Another has been the criminal investigations by police in Spain, Italy and Germany that have turned allegations into hard facts. Also, perhaps, the Bush administration is just more vulnerable since Hurricane Katrina. Now there is a danger we may all get carried away. There are still more facts to be uncovered about the rendition programme: what, for example, is the true extent of British and other European governments' knowledge of, and involvement in, these CIA activities? However, in the fever of CIA plane-spotting that, admittedly, I helped to start, there is a risk of an idea taking hold that somehow all covert activities must be exposed. That would undermine our security - and misses the point. It is neither wrong to fight terrorism nor to use covert means to do so. It is not wrong to collect secret intelligence. But, as decent people within the CIA will tell you, and as I tried to tell that American TV producer, it's just plain wrong to torture.