The new bomb supposedly contained no metal. Does this mean it would have passed through airport detectors unnoticed?
Yes, that would be the case with a magnetometer, if the bomb did not have any metal wiring, which tends to be picked up. Airport security screeners also swab people, luggage and handbags, looking for a variety of substances, including drugs and explosive chemicals. Although they likely wouldn't swab someone's underwear, the chemical might have gotten on that person's luggage and clothes without them realizing it. Chemical analysis may have been a way to detect this type of explosive but airport screeners don't swab every bag.
Would backscatter x-ray machines or millimeter wave scanners deployed at many airports have been effective in spotting the new underwear bomb?
Those scanners are looking for anomalies on a person's body, in particular something that is hard or dense. It depends on the density of the bomb materials, what the ingredients are and the form they took.
[Backscatter picks up the radiation bounced back from the passenger's body and any objects the person may be concealing. Elements such as carbon, oxygen, hydrogen and nitrogen—common ingredients of explosives—create a strong scattering effect visible in images that operators monitor on a screen yet are discernible from the organic molecules in the human body. Millimeter waves, which are shorter than microwaves but longer than infrared, create a revealing picture that can highlight items and determine the precise chemical makeup of an object. Although backscatter and millimeter wave scanners might have given screeners cause to be suspicious of an underwear bomb, neither are used in all airports, and passengers concerned about exposure to radiation can often opt to instead be frisked by security personnel.]
In addition to the original underwear bomb and the 2010 attempts to pack explosives as cargo on aircraft, what other tactics has al Qaeda tried in their search for effective methods of attack?
[Ibrahim Hassan] al Asiri had his own brother place PETN inside his colon and then told him to surrender to the counter-terrorism chief in person and request entry into Saudi Arabia's terrorist rehabilitation program. In August 2009 Abdullah Hassan al Asiri tried to assassinate Saudi Arabia Interior Minister Prince Muhammed Nayef bin Abdul Aziz al Saud, although the PETN explosion ended up killing him and only slightly injuring al Saud. Ironically, al Saud was protected from the full brunt of the blast by al Asiri's body. Less than half a year later, Abdulmutallab tried the first underpants bomb.
In each case, the bomb-makers take into account cultural norms. For example, the Taliban developed a turban bomb, which was employed to assassinate Burhanuddin Rabbani, a former Afghan president and head of the High Peace Council. The tactic was used because Afghans are reluctant to request the removal of a turban.
What has been the most effective means of disrupting terrorism attacks?
As with bombs that were being sent from Yemen to Chicago as cargo, this latest plot was discovered using human intelligence rather than screening procedures and technologies. These plans were disrupted because of proactive mechanisms put in place to stop terrorism rather than defensive approaches such as screening.