Base on a review of empirical data, a report by the Rand corporation, the US governments captive think tank, "concluded that the administration's war on terrorism has not significantly degraded al-Qaeda and that the group has morphed into a more formidable enemy. In fact, al-Qaeda has perpetrated more attacks after September 11, 2001 than before it.

"RAND deduced that the best way to kill a terrorist group is to capture or kill its leaders. This task is best carried out, according to the study, by law enforcement, intelligence, and, if needed, troops from the local country." --Reported here.