The trouble with tracking terrorists...

Is that law enforcement agents are expected to arrest them before they carry out their intentions. This means that investigators have to rely on intelligence as opposed to evidence, which posses an irreconcilable dilemma as Sandra Bell, head of Homeland Security for Britain's Royal United Services Institute, explains in yesterday's Wall Street Journal.

To give you some idea of the scale of the problem Britain faces, Bell says there are currently around 40 terror trials pending, involving some 100 defendants. Couple this with the news that the head of Britain's MI5 released in November - that British intelligence estimates that there may be as many as 200 active terror networks in Britain, involving some 1,600 individuals.

Because law enforcement is expected to disrupt terror plots before they occur, police have to rely on intelligence - intelligence that can be easily manipulated, misinterpreted, and difficult if not impossible to cross check. The consequence of this inevitable dilemma, Bell observes, is that innocent people can be arrested or detained; and guilty people may go free.

To illustrate her point, she cites two examples. The first is the case of the two Muslim brothers whose home some 250 police stormed in June 2005 under suspicion that they were plotting to use chemical weapons. During the raid, one of the brothers was shot in the shoulder. Apparently the intelligence the police were relying on was mistaken as the brothers were later released. Though an independent investigation exonerated the police of any wrongdoing in the case, as Bell writes, "[this] did little to dispel Muslim complaints that they are being unfairly singled out."

While this case was indeed unfortunate, as Bell continues:

Now consider the other extreme: the case of Mohammad Sidique Khan, a Leeds born primary school teaching assistant and the ringleader of the July 7, 2005, bombings that killed 52 people in London. Khan had come to MI5's notice more than a year before the bombings when he was spotted in the company of other terrorist suspects. He was, however, just one of hundreds of suspects caught up in one of many surveillance operations. At the time he was nothing more than a blurred image on a surveillance tape. Investigators did not even know his name. Since the intelligence services had substantial information on the other terror suspects but not on Khan, he was left alone. Given their finite resources, investigators had to prioritize.

Again, investigators were later exonerated of any wrongdoing but, as Bell points out, this did little to mollify public outrage that "[such] a major intelligence gaffe" could occur, and one that resulted in the loss of 52 lives.

Unfortunately, as Bell points out, no new laws or tougher prison sentences "will change the underlying dilemma: the need for the police to act on intelligence rather than evidence to stop potentially devastating attacks."

What to do? Bell''s only recommendation is that authorities should be more open and the public should be more understanding:

They [the authorities] need to have the courage to acknowledge that mistakes will be made and the humility to apologize for them when they occur. And the British public needs to understand that we are moving into a new, grim normality.

While her advice may not seem all that brilliant, does anybody have a better suggestion?