How the CIA identified and killed Al-Qaeda leader Zawahiri

FILE PHOTO: Osama bin Laden sits with his adviser Ayman al-Zawahiri, an Egyptian linked to the al Qaeda network, during an interview with Pakistani journalist Hamid Mir (not pictured) in an image supplied by Dawn newspaper November 10, 2001. Hamid Mir/Editor/Ausaf Newspaper for Daily Dawn/Handout via REUTERS/

Al Qaeda leader Ayman al-Zawahiri was killed in a U.S. strike in Afghanistan over the weekend, the biggest blow to the militant group since its founder Osama bin Laden was killed in 2011.

Zawahiri had been in hiding for years and the operation to locate and kill him was the result of "careful patient and persistent" work by the counter-terrorism and intelligence community, a senior administration official told reporters.