Searches of al Qaeda sites in Afghanistan, undertaken since American-backed forces took control there, are not known to have turned up a significant cache of nuclear materials.

Al Qaeda is closely aligned with the Chechens.

There is evidence that some of al Qaeda's nuclear efforts over the years met with swindles and false leads.

Counterterrorism analysts have known for years that al Qaeda prepares for attacks with elaborate 'targeting packages' of photographs and notes.

Leaders at the top of al Qaeda's hierarchy, the evidence shows, completed plans and obtained the materials required to manufacture two biological toxins - botulinum and salmonella - and the chemical poison cyanide.

The gravest risks from al Qaeda combine its affinity for big targets and its announced desire for weapons of mass destruction.