Very Rare Terrorists Are Very Hard to Find

Spencer Ackerman tries to problematize the conclusion that the underpants bomber incident really represents a grievous intelligence failure. You should read his whole analysis. But in brief, while by definition letting a bomber on an airplane is a failure, based on what was actually known about Abdulmutallab, excluding him from flying would involve erecting pretty substantial barriers to entering the United States in ways that would have real costs. As I said before, the key point about identifying al-Qaeda operatives is that there are extremely few al-Qaeda operatives so (by Bayes’ theorem) any method you employ of identifying al-Qaeda operatives is going to mostly reveal false positives.

Read, for example, this account of looking retrospectively at Abdulmutallab’s time in London. The fact of the matter is that there’s nothing in his behavior during this period that distinguishes him from any number of other young, reasonably devout Muslims living in Britain. He had political opinions that are outside the mainstream for a white Christian living in the United States, but so do virtually all Muslims.

John Burns is a great reporter, but I think this graf in the piece is analytically suspect:

That view, if confirmed, would offer a stark reaffirmation that Britain, the United States’ closest ally, continues to pose a major threat to American security. Critics in Britain and the United States say the British security forces, despite major increases in budgets and manpower in recent years, have not yet succeeded in adequately monitoring, much less restraining, the Islamic militancy that thrives in the vast network of mosques that serve the nation’s 1.5 million Muslims — and on university campuses across the country where nearly 100,000 of the 500,000 students are Muslims, including many, like Mr. Abdulmutallab, from overseas.

It’s just not the case that the possibility of a guy going to the UK, becoming radicalized, going to Yemen, acquiring an idea about how to smuggle explosives onto a plane, boarding a plane in Amsterdam, and attempting to detonate the device constitutes a “major threat to American security.” You don’t want to minimize the threat that a couple of hundred people might get murdered. We punish—severely and rightly—individuals who knowingly murder as few as one person. Murdering a whole plane full of people is very bad and we should try hard to stop it from happening. But the detonation of a plane just isn’t a major threat to our security. Civilian planes have been destroyed before, they’ve crashed before, and the country has suffered a much worse terrorist attack and in a broad sense it’s always turned out okay.

The other point is that monitoring the UK’s 1.5 million Muslims is a lost cause. If you have a 99.9 percent accurate method of telling whether or not a given British Muslim is a dangerous terrorist, then apply it to all 1.5 million British Muslims, you’re going to find 1,500 dangerous terrorists in the UK. But nobody thinks there are anything like 1,500 dangerous terrorists in the UK. I’d be very surprised if there were as many as 15. And if there are 15, that means you’re 99.9 percent accurate method is going to get you a suspect pool that’s overwhelmingly composed of innocent people. The weakness of al-Qaeda’s movement, and the very tiny pool of operatives it can draw from, makes it essentially impossible to come up with viable methods for identifying those operatives.