LONDON -- Egyptian radical Ayman al Zawahri on Wednesday issued his first statement since U.S. special forces killed al Qaeda leader Osama bin Laden in Pakistan, promising to carry on bin Laden’s war against the West.

“The man who terrified America in his life will continue to terrify it after his death,” Zawahri said in the 28-minute video, which was released by al Qaeda’s media branch.

But Zawahri, long bin Laden’s deputy, did not claim bin Laden’s mantle as the head of al Qaeda in the video, an omission that adds to the ongoing debate among terrorism experts over who will lead the terrorist organization.

At a conference on terrorism here, one former jihadist, Noman Benotman, a Libyan who fought in Afghanistan as part of the Libyan Islamic Fighting Group, said he believes Zawahri, who is considered less charismatic and more divisive than bin Laden, won’t lead the organization alone.

Some of the leadership functions, Benotman said, will be assumed by a former Guantánamo detainee, Ibrahim al Rubaish, 33, a cleric from Saudi Arabia who is now the spiritual leader of al Qaeda in the Arabian Peninsula, the terrorist group’s affiliate in Yemen.

Placing Rubaish in a leadership role would let al Qaeda “keep the narrative” of its Saudi roots, Benotman said. Moreover, Rubaish’s four years at Guantánamo elevate his role as a jihadist even as he functions as the spiritual leader for al Qaeda in the Arabian Peninusla, the terrorist group’s Yemeni affiliate.

“To have been a prisoner, it’s very important,” said Benotman, who now analyzes radical Islam at the Quilliam think-tank in London. “No one can question his credibility or his willingness to sacrifice himself for the cause.”

He cast Rubaish as “not militant,” but “a real sheikh, a classic sheikh.” Three other likely candidates to run the terror group, he said, are now in Saudi prisons.

Rubaish’s Guantánamo intelligence profile, made public by WikiLeaks, casts him as an al Qaeda-trained Saudi who went to Afghanistan to fight the Russians in Chechnya but instead joined with the Taliban and then fled to Tora Bora with bin Laden and hundreds of other devotees after the Sept. 11, 2001, terror attacks.

He was among Guantánamo's first captives, held for months in the open-air cages at Camp X-Ray, and took part in its earliest hunger strikes. But his 2005 military intelligence profile, written a year before his release, only hints at his leadership potential.

Another Saudi captive reportedly told Guantánamo interrogators that Rubaish “has some type of leadership role among detainees and strongly influences them.”

The administration of President George W. Bush released Rubaish to Saudi Arabia in 2006 to take part in a rehabilitation program that in his case apparently failed. U.S. officials have provided no specifics on his case, but the Saudi Interior Ministry declared him a wanted man in February 2009.

In Washington, Carnegie Endowment for Peace scholar Christopher Boucek agreed Zawahri and Rubaish could emerge as the new al Qaeda leaders. But Boucek said another former U.S. captive also could lay claim to bin Laden’s mantle.

Abu Yahiya al Libi was never held in Guantánamo but escaped from the U.S. lockup at Bagram, Afghanistan, in July 2005. Boucek called the Libyan a “video savvy poet” who trained as an Islamic scholar and has engaged in combat.