June 10, 2006 -- With al Qaeda in Iraq leader Abu-Musab al-Zarqawi killed in a June 7 U.S. air strike, who will fill the terror vacuum in Iraq. And with al-Zarqawi out of the way, will al Qaeda leader and 9/11 mastermind Osama bin Laden ever be found?
United States military spokesman Maj. Gen. William Caldwell said that the logical successor to lead al-Zarqawi's group is Abu Ayyub al-Masri, an Egyptian. Masri has close ties to bin Laden's number two, Ayman al-Zawahiri, who is also the leader of the group known as the "Egyptian mafia" within al Qaeda.
"Al Qaeda needs charismatic leaders to attract followers," said Alexis Debat, an ABC News terrorism consultant and a Senior Fellow at the Nixon Center. "Al-Zarqawi was a rock star. He was very charismatic. They're going to be looking to replace him with someone who will capture the attention and the minds of the Muslim community. … There are several people. The one we're focusing on is Abu al-Masri, who is an Egyptian."
Although not much is known about al-Masri -- including his real name -- Debat said he is experienced at making explosives and recruiting foot soliders in Africa and Asia for the insurgency in Iraq. He may have more international reach than al-Zarqawi.The U.S. Central Command has put a $50,000 reward on al-Masri's head.
Al-Masri formerly worked as the head of al-Zarqawi's international terrorist network before going to Iraq on the eve of the American invasion in March 2003. He was last seen in Baghdad in 2002, when he was reportedly on a mission to establish an al Qaeda cell that could begin operations once the United States overthrew Saddam Hussein and occupied Iraq.
Al-Masri and al-Zarqawi met at the al-Farooq training camp in Afghanistan, where al-Masri worked as an instructor specializing in explosives. He is thought to be about the same age as al-Zarqawi, who was 38 when he died.
The Hunt for Bin Laden
On the other major front in the war on terror, the most recent reports of bin Laden place him in a part of Pakistan where hiding is easy.
The frequent heavy cloud cover at the location makes satellite surveillance difficult, and bin Laden's captured aides say he knows it and takes advantage of it.
"At nighttime and during cloud cover is the optimal time to be moving around on the ground," said Tim Brown, an imagery analyst for talent-keyhole.com.
And unlike Iraq, there are steep mountains that can limit the line of sight of the CIA's low-flying unmanned predators.
"They're going to be able to see what's directly below them and on the sides but what's around the bend or on the other side of a mountain crest is going to be obscured," said Brown.
Even still, Debat said that after 10 years of tracking him, U.S. intelligence is getting closer to finding bin Laden, not through technology, but through old-fashioned intelligence.
The United States is "increasingly relying on the intelligence services such as the Jordanians, which we know now played a very important role in getting to al-Zarqawi," Debat said. "The problem is that the area between Afghanistan and Pakistan where bin Laden is supposed to be hiding is a no-go area, even for the Pakistani military. The United States military cannot operate there. What it does usually [is] it recruits people on the Afghan side and sends them to Pakistan."
Pakistani troops have run into stiff resistance or been reluctant to run operations in the hostile tribal areas.
"This is why bin Laden has been able to go on for so long and stay in hiding. He knows that area," said former CIA officer, Bob Baer.
There's also the question of ego. Al-Zarqawi's aggressive public posture, personally involving himself in every operation, allowed the United States to slowly but surely track his movements; bin Laden lays much lower.
"He put himself out there on TV, he exposed himself -- it's almost suicidal, the way he did this," Baer said. "He wanted to be a martyr, and we took him out."
ABC News's chief investigative correspondent Brian Ross contributed to this report