Wednesday, November 30, 2005

How Do You Catch Terrorists?

Suppose that terrorists choose targets by maximizing their expected utility. Suppose these guys have rational expectations. In choosing where to strike, they must tradeoff the probabiity of a successful attack, the amount of damage they will cause if successful, their disutility from being killed or captured in the attack, and the financial cost of launching their mission.

If Homeland Security had a good model of how terrorists make choices, would we suffer fewer terrorist attacks? Or would the terrorists anticipate that their moves were predictable and switch over to randomization in choosing their strategies?

The article below suggests that the U.S counter-terrorism does not want to be predictable.

It would interest me whether Homeland Security is "over-investing" in protecting airports over other vulnerable targets. Its intuitive that another airplane hijacking would be unlikely to kill 3,000 people again. If such a plane were taken, this information would spread and people would evacuate. I can't even think of a major other target besides for the Sears Tower in Chicago. If the maximum loss of life from another plane takeover is bounded by 3,000, and if the potential loss of life from other types of attacks is much higher; what does this suggest?

In this horrible setting, I wonder how social scientists can make progress here in investigating how terrorists play "offense" and how Homeland Security plays "defense". Could a good game theorist be useful here advising Homeland Security? Are they doing such advising?

December 1, 2005
Significant Changes in Air Passenger Screening Lie Ahead

WASHINGTON, Nov. 30 - The Transportation Security Administration is making some of the most significant changes in the screening of airline passengers since procedures were revamped after the Sept. 11 terrorist attacks.

The changes include a new type of random search, a revision of the pat-down process and the end of a ban on small scissors and certain other sharp tools in carry-on luggage.

The goal of the changes, which will be announced Friday and go into effect on Dec. 20, is to try to disrupt the now-familiar routine associated with security screening, a routine that federal officials fear would-be terrorists may have studied to figure out ways to circumvent it.

"We don't want the predictability of the system to be used against us," said Yolanda L. Clark, a security agency spokeswoman. "So we are introducing an element of randomness that makes it more difficult to manipulate."

Ms. Clark and other officials from the Department of Homeland Security declined to discuss the changes, saying they would be unveiled in a speech by Kip Hawley, the assistant secretary for homeland security who oversees the security agency. A five-page summary of the new policies was obtained Wednesday by The New York Times.

The summary document says the elimination of the ban on metal scissors with a blade of four inches or less and tools of seven inches or less - including screwdrivers, wrenches and pliers - is intended to give airport screeners more time to do new types of random searches.

Passengers are now typically subject to a more intensive, so-called secondary search only if their names match a listing of suspected terrorists or because of anomalies like a last-minute ticket purchase or a one-way trip with no baggage.

The new strategy, which has been tested in Pittsburgh, Indianapolis and Orange County, Calif., will mean that a certain number of passengers, even if they are not identified by these computerized checks, will be pulled aside and subject to an added search lasting about two minutes. Officials said passengers would be selected randomly, without regard to ethnicity or nationality.

What happens next will vary. One day at a certain airport, carry-on bags might be physically searched. On the same day at a different airport, those subject to the random search might have their shoes screened for explosives or be checked with a hand-held metal detector. "By design, a traveler will not experience the same search every time he or she flies," the summary said. "The searches will add an element of unpredictability to the screening process that will be easy for passengers to navigate but difficult for terrorists to manipulate."

The new policy will also change the way pat-down searches are done to check for explosive devices. Screeners will now search the upper and lower torso, the entire arm and legs from the mid-thigh down to the ankle and the back and abdomen, significantly expanding the area checked.

Currently, only the upper torso is checked. Under the revised policy, screeners will still have the option of skipping pat-downs in certain areas "if it is clear there is no threat," like when a person is wearing tight clothing making it obvious that there is nothing hidden. But the default position will be to do the more comprehensive search, in part because of fear that a passenger could be carrying plastic explosives that might not set off a handheld metal detector.

These new procedures will go into effect at the same time as the security agency continues to expand other measures, like using more bomb sniffing dog teams and installing high-tech devices that blow a short burst of air on passengers to detect traces of explosives. Forty-three of these devices, known as explosive trace portals, have been installed at 22 of the nation's largest airports.

This new category of random checks and the more comprehensive pat-downs can be done without causing significant delays, officials said, because of the enormous amount of time that will be saved because screeners no longer have to confiscate small scissors or tools, a policy change first reported in The Washington Post. These kinds of sharp instruments are now found in about one in four carry-on bags.

All knives will still be prohibited, as well as drills, hammers, saws and crowbars, according to the summary document.

The ban on scissors and other small tools, first imposed after the 2001 hijackers used box cutters to seize four planes, can be lifted, these officials said, because airplane cockpit doors are now more secure, thousands of pilots are now authorized to carry handguns and more federal air marshals now fly on planes.

The changes drew a mixed reaction Wednesday, with some security experts and members of Congress praising them, while others said they were counterproductive.

Representative John L. Mica, a Florida Republican who is chairman of the House subcommittee that oversees aviation security, said the changes were long overdue.

"The threat today is not someone taking over an aircraft with scissors or a knife," Mr. Mica said.

David Castelveter, a spokesman for the Air Transport Association, said the airline industry also supported the changes.

But Jon Adler, executive vice president of the Federal Law Enforcement Officers Association, which represents federal air marshals, said that allowing scissors and small tools on planes was a mistake.

"These items in the wrong hands can become dangerous instruments that can ultimately threaten both air marshals' and travelers' safety," Mr. Adler said.


Anonymous said...

Although the idea of introducing randomness is certainly sensible, it strikes me that the objective of terrorists is more than just blowing things up. I believe that a military expert would say that the purpose of a minefield is not so much to destroy the enemy as to constrain his movements and cause him to do things he would not otherwise do.

One cost of the 9/11 attacks was the direct loss of life and physical damage. A second cost is the cost of maintaining the air security system (and not just the direct TSA cost, but the indirect costs imposed on passengers and society).

The day after 9/11, I suggested that (a) it was the death knell for "old-fashioned" hijacking (because passengers would now automatically resist assuming any hijacking is a suicide attack) and (b) future attacks using the same method are unlikely (at least in the US) once the vulnerabilities that allowed 9/11 are corrected (as they have been). The catch is that even though we are reasonably safe from another 9/11-type attack, that safety is only so long as we continue to pay the costs of maintaining appropriate (and expensive) security. Meanwhile, as suggested in the original posts, terrorists remain free to seek out other vulnerabilities and means of attack.

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