Al-Qaeda still aims to use weapons of mass destruction against U.S

Excerpt: When al-Qaeda's No. 2 leader, Ayman al-Zawahiri, called off a planned chemical attack on New York's subway system in 2003, he offered a chilling explanation: The plot to unleash poison gas on New Yorkers was being dropped for "something better," Zawahiri said in a message intercepted by U.S. eavesdroppers.

The meaning of Zawahiri's cryptic threat remains unclear more than six years later, but a new report warns that al-Qaeda has not abandoned its goal of attacking the United States with a chemical, biological or even nuclear weapon. Read it here.

For the full report and the time line for terrorist attempts at acquiring weapons of mass destruction see A Timeline of Terrorists' Efforts to Acquire WMD