Back in September, Rand analyst Seth Jones helped us put together a list of senior al Qaeda leaders who were still at large. The list included senior commander Abu Obaidah al-Masri who, it was announced this week, died about two months ago. I spoke with Jones today about the implications of al-Masri's death for the al Qaeda leadership. He stressed that it's a mistake to think of the organization as a bureaucracy where specific offices are filled after they are vacated:

People get moved around quite a bit based on their competencies. Less-informed people talk about al Qaeda leadership in terms of numbers, as if someone was "number three or number four." I don't think the command and control structure works that way. There's a range of people who go through the different positions. There is not one job that any of these guys do. 

But this is not to say that al-Masri's death is insignificant. He played a major part in several high-profile operations and, as Jones noted, it can be hard to find someone with his particular skillset:

He played an important role both on the international front in the [2006] transatlantic plot, and was involved in a couple of other plots that European government are investigating. Recently he also played quite an important role with the Afghan insurgency. It takes time to replace competent senior al Qaeda operatives.