Terror by the Numbers

Random searches are as much about the appearance of safety as safety itself

Let's play a game. You be New York City, and I'll be the terrorist.

You don't know when or how I'll strike. You also don't know what or where I'll attack—subways seem like my new target of choice, but they could be just a passing fad. You know that I want to kill people, but you don't know how many, because to me sowing fear might be as important as taking lives. And you don't know whether I'm willing to sacrifice my life in order to take others'. A burglar wants loot, a rapist wants sex, but what I want is a little fuzzy—so predicting my next move is a dice roll.

I'm not your only problem. There are also my potential victims, the people who live and work in New York City. You've got to protect them while making sure that you don't cause more disruption than my potential attack. You've got to convince people that they are being protected, without scaring them so much that their anxiety shuts down the city.


imageEvents like 9-11 or the London bombings are human dramas, but the policy choices they force are supposed to be cold calculations about the game that killers and protectors play, the costs they bear, and the chances they take.

Last week the New York Police Department began random searches of passengers' bags on subways, buses, and commuter trains. Officers aren't targeting every bag and—according to Police Commissioner Ray Kelly—won't use any profile to target particular subway riders. That means the cops are taking a chance that they will search enough bags to catch a bomber—if there is a bomber—before one strikes, or at least dissuade him from trying to get through the turnstiles.

It's a shot in the dark, but so is the terrorists' mission, says Columbia business professor Geoffrey Heal. "There's a lot of chance in it. Presumably they don't know which train they're going to get on, what car they're going to get on, how many people will be in it," he tells the Voice. "All of this is decided at the last minute."

Heal's expertise on terrorism concerns the choices that governments make to defend against the threat of random violence. In this calculus of security, there are certain givens, says Heal. One is that suicide bombings are easy to pull off as long as you've got volunteers. "The first few times it happens," he adds, "it's virtually impossible to stop."


The surest way to protect the subway system from bombs would be to screen every passenger's bag. But that would not only be enormously expensive in terms of time and manpower, it could have a human cost. The subways would become very inconvenient to ride, more people would drive cars, and there'd be more fatal road accidents. That's not to mention that the long lines of riders waiting to get screened would pose a tempting target.

So searching every single bag is out. But what about searches using a profile, so that not as many innocent people are inconvenienced? Besides the civil liberties questions, there's a basic problem with targeted searches: The targets know they've been tagged. "This transparency . . . enables the system to be reverse engineered," wrote M.I.T.'s Samidh Chakrabarti and Aaron Strauss in a 2002 paper about screening air passengers. "You know if you've been questioned. You know if you're asked to stand in a special line. You know if you've been frisked. All of this open scrutiny makes it possible to learn an anti-profile to defeat [the screening system], even if the profile itself is always kept secret."

Random searches, of course, mean there's a chance that a bomber will get through. With 4.5 million subway riders daily, the potential bomber is a needle in a human haystack. The cops' goal is a psychological one, aimed at terrorists, says one ex-NYPD officer: "Keep them thinking that they may be searched at any time and any place."

A terrorist might still gamble that he or she will get through the screening, because a subway system is really hard to defend. While the London bombings took far fewer lives than 9-11, they actually posed a tougher task to security agencies, because subways are meant to be open and easily accessible.

"That's the downside," Heal says. "The upside is you can kill far fewer people in public transport than in airlines." For that reason, he adds, subways are "very second-best as far as the terrorists are concerned. It represents a move to a lower-value sort of target."

That terrorists are switching to lesser targets could be a sign that the airlines have become more secure since the 2001 attacks. But it also reflects a reality of the security business: As you harden one target, others become more appealing. Israel is a case study of this shifting risk. El Al employs legendary security measures, so terrorists don't bother trying to hit Israeli jetliners. Instead they target malls, buses, and nightclubs. The casualties are lower, but there are still casualties.

"The important thing to understand is that security that moves a threat around is useless. So if we spend billions saving New York City subways and the terrorists go into movie theaters, we have wasted billions of dollars," says Bruce Schneier, a California-based security expert. "Defending the targets is the wrong way to think, because for the terrorist it doesn't matter if he hits the subway or a nightclub or a restaurant or a supermarket or the line at the DMV to renew your driver's license or the Oklahoma City federal building."


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