As al Qaeda recovers from the SEAL raid that killed Osama bin Laden and builds a new leadership team, its inner circle has undergone a major metamorphosis, thanks to the arrival since late last year of the long- lost al Qaeda Iran cadre. After 9/11 and the toppling of the Islamic Emirate of Afghanistan, a major block of al Qaeda’s founding fathers fled to Iran, and lived under some kind of loose control from Tehran for years. Now they have been allowed to leave and have returned to Pakistan. This cabal of experienced operatives has been welcomed home and will be a defining element in the new post-bin Laden al Qaeda, along with his long time Egyptian deputy Ayman Zawahiri and the up-and-coming Pakistani terror mastermind, Muhammad Ilyas Kashmiri.

In late 2001 and early 2002, as bin Laden and Zawahiri fled from Afghanistan east into Pakistan, another smaller exodus of al Qaeda leaders went west into Iran.  The Iranians detained many of them.  For the next nine years they remained there, their status never clear to outsiders.  They were not free to leave Iran, but they do not seem to have been full-time prisoners either.  The Iranians occasionally hinted that they might be ready to trade these al Qaeda operatives for anti-regime dissidents like the Mujahedin e Khalq group that was captured in Iraq during the 2003 invasion. But no deal ever emerged.  Iran may also have found them to be useful hostages—effectively helping to keep al Qaeda from attacking Iranian targets.  Washington accused the Iranians of turning a blind eye to the exiles’ support for al Qaeda attacks in both Iraq and Saudi Arabia from their Iranian homes.

Their departure from Iran late last year is as mysterious as their time in country.  Some unconfirmed reports have hinted at a prisoner exchange with al Qaeda in Pakistan, which had captured a senior Iranian spy; there may have been a trade with Tehran for the exiles. Another theory: as U.S.-Iranian relations deteriorated in 2010 over Iran’s nuclear program and Tehran’s suppression of dissidence at home, the regime just let the al Qaeda teams leave quietly for Pakistan so they could go back and harass America.

Al Qaeda and Iran have a very complex relationship. The terror cell is extremist Sunnis, while Iran is majority Shia; the two sides tend to hate each other with a violent passion.  Al Qaeda in Iraq and Afghanistan has attacked Shia with a vengeance. But they find common cause in their mutual hatred of America; both can see the virtue in having more anti-U.S. violence, whatever the source. The two sides have engaged in quiet tactical cooperation dating back to the mid-1990s.

Whatever the Iranian motives in letting them go, the old timers came back at a critical juncture for al Qaeda. Drone strikes had weakened the terror cell’s core even before the CIA found bin Laden in Abbottabad. The experienced refugees from Iran were quickly reabsorbed into al Qaeda.

Now they are set to be an important part of the new post bin-Laden operation. Several are Egyptians like Zawahiri. The most prominent of these is Sayf al Adl, his nom de guerre, or Muhammad Salah al Din Abd al Halim Zydan.  Once a colonel in the Egyptian army, Sayf joined Zawahiri’s Egyptian Islamic Jihad in the 1980s. When Zawahiri and bin Laden merged their terror gangs to create al Qaeda, Sayf became a senior military operative for al Qaeda and was very close to bin Laden.  In 2001 Sayf took several bin Laden family members with him to Iran, including Osama’s son Saad bin Laden (he returned with Sayf to Pakistan late in 2010). While living in Iran, Sayf wrote a biography of Abu Musaib al Zarqawi, al Qaeda’s notorious terror chief in Iraq, lauding his battles against the American occupation forces and criticized Iran for not helping the jihad in Iraq enough.  Now some reports have suggested that Sayf may be acting chief of al Qaeda while Zawahiri finds a new safe house, but these too are unconfirmed.

Among the other al Qaeda operatives who have returned to Pakistan from Iran recently is another Egyptian named Abdullah Ahmad Abdullah alias Mohammad al Masri. With Sayf, he was a key player in the attacks on the U.S. Embassies in Tanzania and Kenya in August 1998.  Sulaiman Abu Ghaith is a Kuwaiti who was an active fund-raiser for al Qaeda before 9/11 and one of its most prominent spokesmen before fleeing to Iran in 2001. Abu Hafs al Mauritani, whose real name is Mahfouz Ould al Walid Khalid al Shanqiti, is a Mauritanian citizen with strong religious scholarship credentials.

The Iranian exiles’ return came as al Qaeda in Pakistan was under sustained attack from the American drones. The leadership must now be concerned that the mountain of computer hard drives seized in Abbottabad will unravel their hiding places and lead to more drone operations.  So a period of reconstruction is likely. A further wrinkle: recent reports of a new lawsuit suggesting that Tehran may have been complicit in al Qaeda’s 9/11 attacks.

One other faction will have a major role in fashioning the new order: al Qaeda’s Pakistani terrorists.  After all, they know their country better than any outsider.  The man who stands out in this crew is Muhammad Ilyas Kashmiri.  Trained by the Pakistani intelligence service and its commando school, he has fought in Kashmir, India, Afghanistan and at home in Pakistan for decades.  He is the mastermind behind several al Qaeda plots in Europe.   Kashmiri was Al Qaeda’s handler for the American David Headley who helped plan the November 2008 attack on Mumbai and whose testimony this week in a Chicago court has demonstrated the complex links between al Qaeda, its Pakistani terror allies and the Pakistani army.  Kashmiri sits at the center of all of those linkages.

Al Qaeda’s bylaws are very specific about the succession issue.  As deputy to bin Laden, Zawahiri should take on the title of Amir of al Qaeda.  Zawahiri has decades of credentials as a terror leader going back to the assassination of Anwar Sadat and is al Qaeda’s most prolific theoretician.  But the ex-Iranian exiles and the Pakistani home team will play important roles.  Rumors of differences of opinion between the various al Qaeda honchos should be taken with a grain of salt.  Doubtless they have their quarrels. But what unites them is far more important than these differences:  they are determined to avenge bin Laden’s death and strike America.