FBI 'Most Wanted Terrorist' Saif al-Adel is likely to be the next chief of al-Qaeda after Ayman al-Zawahiri was killed in a US drone strike. He's a former Egyptian Army officer and is wanted in the 1998 US embassy bombings which led to 250 deaths. He also oversaw the 'Black Hawk Down' ambush of US forces, killing 18 in 1993.