TSA is responsible for securing all modes of transportation while facilitating commerce and freedom of movement for the traveling public. In performing its responsibilities, TSA is guided by risk-based planning, which generally involves a consideration of threats, vulnerabilities, and the criticality or consequence of an attack if it were to be carried out. Specifically, in its approach to securing the domestic aviation sector, TSA maintains numerous programs that provide a layered approach to security, including intelligence gathering and analysis, checking passenger manifests against watch lists, and assigning undercover air marshals to certain flights. The general public associates TSA mainly with its security effort at airport passenger checkpoints. One primary goal of the passenger checkpoint screening program is to provide for the safety and security of persons and property on an aircraft against the introduction of an unauthorized weapon, explosive, or incendiary. As we reported in April 2007, TSA continues to modify its checkpoint screening program based on a number of factors including passenger feedback, risk-based planning, and its own internal review and testing process. TSA’s well-publicized recent policy change in response to the alleged transatlantic bomb plot of August 2006 is an important example of risk-based planning. Known as the 3-1-1 rule, this procedural change prohibits liquid, gel, or aerosol items over 3.4 fluid ounces in carry-on luggage; in addition, all liquid and gels should be placed in a 1-quart bag, and only one 1-quart bag is allowed per passenger. TSA focuses on the checkpoint screening process as a primary means of detecting prohibited items. Items that TSA has prohibited passengers from bringing aboard an aircraft include, among other things, firearms and knives; gasoline and lighter fluid; disabling chemicals, including chlorine and liquid bleach; and many additional items that may be seemingly harmless but could be used as weapons. During the passenger screening process, transportation security officers follow standard operating procedures and utilize technology such as walk-through metal detectors and X-ray machines to detect prohibited items either on a passenger’s person or in his or her carry-on luggage. The passenger checkpoint screening process is composed of the following three elements: Transportation security officers (also known as TSOs) screen all passengers and their carry-on luggage prior to allowing passengers access to their departure gates. Among other responsibilities, transportation security officers attempt to detect prohibited items that passengers may try to carry beyond the security checkpoint. Technology is used during the screening process, which primarily consists of walk-through metal detectors, X-ray machines, handheld metal detectors, and explosive trace detection (ETD) equipment. Standard operating procedures establish the process and standards by which transportation security officers are to screen passengers and their carry-on items at screening checkpoints. The process of screening a passenger who continues to alarm the walk- through metal detector provides an example of how these three elements intersect. According to TSA’s Screening Checkpoint Standard Operating Procedures manual, a passenger who continues to alarm the walk-through metal detector must be screened using a hand-wand search. Passengers may alternatively request a full-body pat-down search. The manual describes the process that transportation security officers are to follow during the additional screening, which includes the use of ETD swabbing and a pat-down of the passenger to detect any irregularities in their body contour that could represent concealed items. TSA faces a significant challenge in balancing security concerns with efficient passenger movement. In our April 2007 report, we described how TSA monitors transportation security officer compliance with passenger checkpoint screening procedures through its performance accountability and standards system and through testing. Compliance assessments include quarterly observations of transportation security officers’ ability to perform particular screening functions in the operating environment, quarterly quizzes to assess their knowledge of procedures, and an annual knowledge and skills assessment. TSA conducts tests to evaluate, in part, the extent to which transportation security officers are able to detect simulated threat items hidden in accessible property or concealed on a person. TSA modifies its standard operating procedures based on the professional judgment of TSA senior-level officials and program-level staff, daily experiences of airport staff, complaints and concerns raised by the traveling public, and an analysis of risks to the aviation system. For example, in December 2005, TSA modified its prohibited items list to allow passengers to carry certain scissors and tools as long as they did not exceed a certain length. TSA’s stated purpose in removing certain scissors and tools from the prohibited items list was to shift the focus of transportation security officers from items considered by TSA to pose a low threat to items considered to pose a high threat. Investigators found instructions on the Internet for creating both an IED and IID and purchased the components from the Internet and from a local store for approximately $150. The IED was conceived as a two-part device—a detonator component that, on its own, could function as an IED, and a mixture of fuel and oxidizer that would require the explosion of the detonator. Although the detonator component could be considered an IED, for the purposes of this report, we are referring to the combination of the detonator and the liquid explosive as a single IED. Information about liquid explosives was publicly available on several Web sites and discussed in media articles related to various terror plots, including the failed London subway bombing of July 21, 2005, and the transatlantic bomb plot of August 2006. In addition, we obtained information about creating an IID from the Internet. We also found videos on the Internet of the intense fire resulting from an IID. One of the components for the IID is a liquid that TSA prohibits passengers from bringing through security checkpoints. Specific details regarding the device components and the methods of concealment we used during our covert testing are classified by TSA; as such, they are not discussed in this testimony. A group of tests conducted in February 2006 and July 2007 show that the IED proposed for this investigation functions as intended. In 2006, within the scope of our original covert testing report, we worked with a law enforcement organization in the Washington, D.C., metro area to confirm that the detonator would function as an IED. A test performed by local law enforcement officials confirmed that the detonator would cause damage to an aircraft and threaten the safety of passengers. Because our proposed IED for this investigation was composed of two parts (the detonator and the liquid explosive), in July 2007 we sought assistance to confirm that this more complex IED would function as intended. Several tests conducted at a national laboratory demonstrated that this IED can function as intended, with the initial explosion by the detonator successfully causing the liquid explosive to detonate in several tests. Explosion data indicate that this device exploded with a force sufficient to cause severe damage to an aircraft. The IID is a far simpler device. Our work with a law enforcement organization in the Washington, D.C., metro area in February 2006 confirmed that the components of the IID (one of which is a liquid) could function as intended, causing damage to an aircraft and threatening the safety of passengers. Our investigators devised methods that would allow them to conceal the prohibited components for these devices from transportation security officers. During this planning phase, they considered publicly advertised TSA policies related to liquids and other items, including prohibited items. They also judged that some components could be hidden in either their carry-on luggage or on their persons. They developed covert test procedures to challenge TSA screening measures using these components and methods. Specific details regarding the methods of concealment we used are classified by TSA; as such, these details are not discussed in this testimony. By using various concealment methods, our investigators demonstrated that it is possible to bring the components for several functioning IEDs and one functioning IID through checkpoints and onto airline flights without being challenged by transportation security officers. In most cases, transportation security officers appeared to follow TSA procedures and used technology appropriately; however, we uncovered weaknesses in TSA screening procedures and other vulnerabilities as a result of these tests. For example, although transportation security officers generally enforced TSA’s 3-1-1 rule, we were able to bring a liquid component of the IID undetected through checkpoints by taking advantage of weaknesses we identified in TSA’s policies based on a review of public information. TSA determined that specific details regarding these weaknesses are sensitive security information and are therefore not discussed in this testimony. We did not notice any difference between the performance of private screeners and transportation security officers during our tests. From March 19 through March 23, 2007, two investigators tested the TSA checkpoint screening process at a number of U.S. airports. Transportation security officers did not interact with our investigators at every airport. Interactions that did occur included the following: On March 19 and March 20, 2007, transportation security officers advised our investigators to use a 1-quart clear plastic bag rather than the larger bags they were using, but did not require them to do so before passing through the checkpoint. Also at another airport, on March 23, 2007, a transportation security officer did not allow one investigator to bring a small, unlabeled bottle of medicated shampoo through the checkpoint. This was a legitimate toiletry item used by one of our investigators. The officer cited TSA policy and stated that since the bottle was not labeled, “it could contain acid.” She did not allow our investigator to bring the unlabeled medicated shampoo bottle through the checkpoint. However, a liquid component of the IID—despite being prohibited by TSA—was allowed to pass undetected through the checkpoint. We had identified this weakness based on a review of public information before performing our tests. From May 7 through May 9, 2007, two investigators tested the TSA checkpoint screening process at a number of U.S. airports.