Peter Taylor: The trail to Osama Bin Laden
I remember interviewing Cofer Black, CIA director at the time of 9/11, two years later and asking him why Osama Bin Laden was still at large. He said he was sure of one thing.
"I am absolutely optimistic that he will be rendered to justice," he told me.
"As with most criminals, sooner or later we will get you. His days are numbered."
Perhaps those days were numbered rather longer than Mr Black would have hoped for - but they came to a dramatic end on Monday.
The bloody endgame came in a hail of gunfire - not, as expected, in a remote cave in Pakistan's Tribal Areas but astonishingly less than 50 miles (80km) from Islamabad in an exclusive villa in Abbottabad, a military town that is a cross between Sandhurst and Aldershot.
Even more astonishingly, it appeared that Bin Laden had been living there for about five years.
The fact that Pakistan's famed intelligence agency, the ISI, claimed to know nothing about who was living behind the compound's very high walls is almost beyond belief.
I always thought that in the end America would track Bin Laden down and fulfil President George W Bush's promise that he would be taken "dead or alive".
I recall reflecting recently that 2011 - the symbolic 10th anniversary of 9/11 - was to be the most likely scenario, and had no doubt that America was pulling out all the stops to meet that emotional deadline.
I instinctively felt that one morning I would wake up, switch on the news and hear that Bin Laden had been killed. On Monday morning, I did.
The world's most wanted man was never going to be located via telephone intercepts or electronic surveillance.
Bin Laden and the praetorian guard around him knew that using any form of electronic communication was tantamount to a death warrant.
Communication had to be done through trusted individuals and couriers who would carry missives and Bin Laden's recorded "messages to the world" in stages by hand to their ultimate destination - whether it be to his comrades in the leadership of "core" al-Qaeda or to al-Jazeera and other broadcasting outlets in the Gulf states.
It was like the Pony Express carrying mail across America in the days of the old Wild West.
It always seemed obvious that the most likely route to Bin Laden was by following one of his couriers. Someone had to deliver the tapes to al-Jazeera. That was probably the beginning of the trail back to Bin Laden.
Couriers apart, I suspect that human intelligence of some kind probably played a vital role in locating Bin Laden.
The same requirement was needed to target members of al-Qaeda and the Taliban by the US pilotless drones that have done so much damage to America's enemies in the tribal areas of Pakistan.
The CIA and their partner intelligence agencies would recruit agents in Pakistan who would be smuggled across the border to provide the CIA's forward operating bases in Afghanistan with detailed intelligence to pinpoint the whereabouts of specific individuals.
The drones would then be programmed and the targets taken out. The agents would - no doubt - be suitably rewarded.
I find it difficult to believe that human intelligence was not used in a similar way to target Bin Laden.
How else would America's Navy Seals not only know where Bin Laden - codenamed "Geronimo" - was hiding but exactly where he was likely to be inside the compound. If there was such an informant he is now likely to be a very rich man.
Unless, of course, the human source or sources turned out to be the ISI who told the CIA where Bin Laden was - on condition that its fingerprints could never be traced.
It is almost beyond belief that if Bin Laden had been living under the ISI's nose for five years, the ISI knew nothing about it.
But that's venturing into the realms of conspiracy…
Peter Taylor presented the BBC2 series The Secret War on Terror and is the author of a new book, Talking to Terrorists: A Personal Journey from the IRA to al-Qaeda.