Newly released documents show London was aware of the threat posed by the al-Qaeda leader in December 2000

State Department urges citizens to maintain high level of vigilance and 'practice good situational awareness' while abroad

Critics on right and left see last year's US withdrawal from Kabul as a show of ineptitude that will make Afghanistan a hotbed of anti-American Islamic groups

2 missiles hit home of terror chief without sign of blast and Washington says no one else was injured -- suggesting use of Hellfire R9X, said to dice targets with 6 large blades

US officials built a scale model of the safe house where Ayman al-Zawahiri had been located, aiming a tailored airstrike at the home's balcony where they learned he enjoyed sitting

Slain terror chief was crucial in shifting jihadi movement to target US; 9/11 made Bin Laden American enemy No. 1, but attacks likely wouldn't have succeeded without his deputy

President says US operation delivered justice for families of 9/11 victims; senior US official says safe house used by Ayman al-Zawahiri owned by Taliban leader's aide

White House officials confirm successful counterterrorism operation, says there were no civilian casualties; US ground team has since pulled out, senior intelligence official says

Ayman al-Zawahiri speaks of 'Judaization of Jerusalem,' mentions US withdrawal from Afghanistan, but not Taliban takeover -- suggesting the footage may not be recent

With unconfirmed rumors swirling over fate of Al-Zawahiri in wake of Abu Muhammad al-Masri's killing in Iran, many analysts point to Saif al-Adel as next leader