Terrorism experts say that Ayman al-Zawahiri, currently the No. 2 of al-Qaida, is well-positioned to take the helm of the terrorist group. This picture is from an online video released on Sept. 2, 2006.
Imam Feisal Abdul Rauf — seen here at a March rally — co-founded a project to develop a Muslim center near ground zero. He believes that Osama bin Laden's death will improve perception of Muslims.
Henny Ray Abrams/AP
Homeland Security Secretary Janet Napolitano said a warning will only be issued if there's specific information about a credible threat. Still, on Sunday night her department warned state and local law enforcement to be prepared for the possibility of an attack.