...seizing the enemy without fighting is the most skillful. - Sun Tzu, Art of War
The terrorism threat hasn't changed. This is still an active war. Although our nation has not been successfully attacked (due to the efforts of counter-terrorism operations world-wide) within the last eight years, doesn't mean we are not at risk. Quite the opposite I would argue. We have entered a period of time where the average American has been lulled asleep by the absence of a spectacular terrorist event. Terrorists use apathy to their advantage. In particular, Osama Bin Laden's al-Qaeda, and host of other terrorist networks, have been known to wait years before launching an attack. During this period of downtime, they meticulously plan their next catastrophic event. Keep in mind that Bin Laden declared War against the U.S. in 1996, but 9/11 didn't happen until 2001. Terrorists are evil, intelligent and deadly, but not infallible.
Terrorists will use what works. Just as our military gages their efforts by completing AARs (After Action Reports/Reviews) and U.S. Law Enforcement tactical teams conduct post-raid briefings, terrorists take note of how effective their last attack was and seek to improve on their destructive results. In order to understand terrorist attack methods, you have to look at roughly the last 50 years of terrorist attacks to categorize their assault methods. Basically, the most probable terrorist attacks (listed in their order of preference) are shown below:
The value in understanding this as a law enforcement officer is that once you know how the enemy attacks, you can come up with methods to mitigate the risks. Before looking at those possible methods, you need to have a clear understanding of how a terrorist cell works.
Every terrorist group operation will use the following players:
Support Cell: Their task is to provide the finances, materials, documents, passports and other logistics for the attack to take place. They operate low key and this cell can operate with fewer than 5 members. Their activities are seemingly innocuous and members performing those functions can be the elderly, middle aged women and children.
Intelligence Cell: These terrorists are specifically trained to conduct intelligence activities and target surveillance. They will use electronic and other means to gather information, such as the Internet, videos, blueprints, direct observation, etc. In many instances, historically, terrorist intelligence cell members have infiltrated the target location months in advance as low-level employees (janitorial, secretarial, delivery personnel) of the organization so that the later stages of their intelligence gathering activities are conducted internally giving them more precise information, such as guard rotations, security precautions, and placement of intended victims.
Operator Cell: The killers. These individuals will use everything useful that has been provided by their complementing elements (Support and Intelligence Cells) to execute the attack. The physical size of the target, defensive posture of the facility and method of attack will determine the number of cell members. It is important to note that the individual cell members, with exception of the cell commander, will probably NOT know their intended target until nearly the last minute. This is done for operational security measurers. If one operator is picked up as the group nears the execution phase of the attack then the overall plan is still not completely compromised, because the target location is still undisclosed within the group itself. The 9/11 attacks, for example, Bin Laden himself did not know the exact date of when the attack would occur until only a few weeks prior. One of the operational commanders of the hijackers, Mohammed Atta, reported to Khalid Sheikh Mohammed only a month beforehand the 9/11 target date. It was then that Bin Laden was told when his operators would unleash the worst terrorist attack on U.S. soil in our history. The point here is that information and operations are compartmentalized to maintain secrecy.