The death of Mustafa Abu Yazid (aka Sheikh Saeed al Masri), who was killed in an airstrike earlier this month, is a significant blow to al Qaeda. Terrorists don’t come with more established credentials than Yazid. He served side-by-side with Ayman al Zawahiri, al Qaeda’s number two, since at least the early 1980s when the two were implicated in the assassination of Egyptian President Anwar Sadat.