Tracking key terror suspects
The path that led the CIA to Osama Bin Laden's doorstep was a long and complex one.
Unlike in the hunt for Iraq's former president Saddam Hussein, the chances of one of the al-Qaeda leader's close associates betraying him for a US$25m reward were always going to be remote.
Such was the intense loyalty of the tiny number of people who knew his whereabouts that we now know that even one of his wives was prepared to rush, unarmed, at the heavily armed US assault team that came for him on that morning of 2 May.
Saddam Hussein, for all his body doubles, his loyal Baath acolytes and his highly-trained bodyguards, was betrayed and arrested within nine months of his going on the run - his secret hiding place near Tikrit revealed to the Americans by someone who is now said to be enjoying the fruits of his reward under a new identity in the US.
By contrast, Bin Laden, strikingly tall, instantly recognisable with no real "home country" to hide in, remained at large for nearly 10 years after the 9/11 attacks and evaded his enemies more than once before then.
But to put this in perspective, Bin Laden is only one of a whole multitude of individuals being tracked and sought by intelligence and law enforcement agencies all over the world.
The connections between them - sometimes real, sometimes tenuous, sometimes wrong - are mind-bogglingly complicated.
So how do they keep track of them and how do they make sense of it? Where are the patterns that can actually lead investigators to identifying and stopping someone before, say, they plant a bomb?
Before the 9/11 attacks much of this work of trying to join up the dots was literally done by hand.
At CIA headquarters at Langley, Virginia, there was said to be a large wall in one room covered with handwritten names festooned with arrows linking them to others. That work has long gone digital.
Among the software used by intelligence agencies and police forces is something called Social Network Analysis, provided by the Cambridge-based firm i2.
This, says i2 senior vice president Charles Watson, mostly has nothing to do with social networking sites Facebook or Twitter. Instead, it is a way of scientifically analysing all the connections and interactions between suspect individuals or their organisations.
Mr Watson cites the example of Operation Red Dawn, the 2003 hunt for Saddam Hussein.
"Social network analysis looked at everyone who knew him - his driver, his cleaner, his bodyguards, starting with the outer periphery and working inwards," he said.
By finding tiny connections between them, says Mr Watson, the US military was able to identify and locate many of the regime's key figures in hiding, names that had appeared on their "Wanted" deck of cards.
"Technology is the only thing that can connect all these dots," he said.
He describes how as targets are tracked using phone records, intercepts, surveillance and human informants, all the collected data is put into the software tool and within seconds relationships start to emerge.
In the case of the hunt for Bin Laden, Mr Watson would not be drawn on whether or not i2's software was used.
But US intelligence has revealed that by August 2010 the CIA had identified the satellite telephone number of his most trusted courier and that enabled counter-terrorism investigators to zero in on everyone he contacted.
They began to analyse the pattern of life inside the Bin Laden residential compound in Abbottabad - who was coming in, who was leaving, at what times, and what was happening inside the compound.
The US National Geospatial-Intelligence Agency (NGA), based at Bethesda, Maryland, was able to put detailed maps together and in the final weeks before the raid, the software which had played such a crucial part in identifying key operatives was used less as the hard military planning took over.
Mr Watson is adamant there is no question of the software getting carried away and making false decisions.
"A human being is in charge at all times," he says.
But surely, I asked him, when you are dealing with such vast amounts of data and names there must be a risk of false information slipping into the mix?
What would happen, for example, if a detainee supplied a false lead either deliberately or simply to make his captors stop what the US euphemistically describes as "an enhanced interrogation"?
"A machine will be objective," he answered. "So if there is a wrong connection derived from an interview under duress then it will pick that up and it will stand out from the rest."
It sounds deceptively simple and of course by its very nature, there is something rather Orwellian - almost 1984 and Big Brother is Watching You - about the whole murky business of tracking and monitoring suspected terrorists.
But Mr Watson ends on a note of caution, an admission that however effective the software, it is only as good as the data that's put into it.
"The terrorist threat is evolving", he said. "I think its getting harder [to stop] as there are individuals we've never heard of, the so-called lone wolves.