Editor's note: Paul Cruickshank is an analyst on terrorism for CNN and Alumni Fellow at the NYU Center on Law and Security New York (CNN) -- The killing of Osama bin Laden is "an enormously significant moment in the fight against al Qaeda terrorism," and there is no one poised to take his place as the group's leader, says CNN terrorism analyst Paul Cruickshank. President Obama announced Sunday night that U.S. forces killed bin Laden in a mansion outside the Pakistani capital of Islamabad. The strike came as the nation approaches the 10th anniversary of the al Qaeda attacks on September 11, 2001, that killed almost 3,000 people in the United States. "Even after 9/11, bin Laden continued to be the strategic guiding force for al Qaeda, signing off on the biggest operations, according to western officials," Cruickshank, an Alumni Fellow at the New York University Center on Law and Security, said in an interview. "He was the linchpin of al Qaeda. Without him, al Qaeda could fracture. There are lots of centrifugal forces within al Qaeda, people with different ideologies and agendas. Bin Laden was able to unify them. He's irreplaceable. There's no one with his level of charisma, fame or visibility." Cruickshank: "I think that in the short term, there could be a spike in activity, with more people being recruited, because he's going to be a martyr figure in the short term. But in the medium term, they're really going to feel the loss. He was very good at coming up with messages that would unify al Qaeda, for instance in the 1990s focusing on the United States, that was a way to unify all these different factions, different nationalities and agendas -- and picking on issues such as the cartoon controversy to unify al Qaeda. Now without bin Laden, they will likely lose some of that unity. Coming after a backlash against al Qaeda in the Muslim world -- the emergence of a powerful critique of al Qaeda from fellow Jihadists for killing so many Muslims and civilians -- and the Arab spring that has reduced al Qaeda to virtual irrelevance in much of the Arab world and removed grievances they were able to exploit, this is a hammer blow to al Qaeda. The threat of al Qaeda won't go away anytime soon, as the thwarting of a serious al Qaeda plot against Germany last week demonstrated. Bin Laden's ideology has been spread too wide for that. But without the guiding hand of its founder, the al Qaeda organization may now begin to unravel."