By Pam Benson
The arrest of Osama bin Laden's son-in-law, who had been living in Iran for the past decade, has once again raised questions about whether the Iranian government is providing a haven or barrier to the terror group.
Al Qaeda and its members held under "house arrest" in Iran over the past decade have had a complicated relationship with the Tehran regime, one which allowed the detainees to often times continue supporting the terror group's operations in the region.
Current and former U.S. officials say al Qaeda in Iran managed to be fairly active in facilitating the movement of money and people into Pakistan where the core leadership has safe haven in tribal areas.
"They helped move people in and out of FATA through Iran for operational reasons," one former senior counter-terrorism official told CNN.
Last October, the U.S. government offered a $12 million reward for two Iranian based men who were described as al Qaeda financiers responsible for the movement of money and fighters in the region.
According to the State Department, Muhsin al-Fadhli helped move operatives from Iran to destinations in Europe, North Africa and Syria, and used a network of jihadist donors to send money to Syria. His deputy, Adel Radi Saqr al-Wahabi al-Harbi, is said to have facilitated the travel of extremists through Iran to Iraq and Afghanistan.
"We will continue targeting this crucial source of al Qaeda's funding and support, as well as highlight Iran's ongoing complicity in this network's operations," Treasury Undersecretary David Cohen said at the time.
It's not that Iran and al Qaeda are close buddies. They are religious rivals with the vast majority of Iranians from the Shia sect of Islam while al Qaeda is a Sunni organization that has frequently targeted Shia communities and mosques.
Their relationship has often been antagonistic – but they do share a deep hatred for the United States. Even with that, Iran has shown what the former counterterrorism official referred to as "some sensitivity" to U.S. concerns about al Qaeda's presence in the country, fearing an American response.
The al Qaeda terrorists fled to Iran after the U.S. invasion of Afghanistan in 2001 and have been mostly held under "house arrest," closely monitored and limited in movement by Iranian authorities.
How much leeway they are allowed depends on the current state of play.
"The role of these guys seemed to go up and down, dependent on the broad state of U.S.-Iranian relations, the overall Sunni-Shia relations and even at times (it seemed) local decisions," a former senior intelligence official said. "Sometimes more active, sometimes less active, sometimes tightly controlled, sometimes less so."
Current and former U.S. officials believe there are still a small number of high-level al Qaeda figures in Iran.
Of greatest interest to Western intelligence agencies is Saif al-Adel, a top military commander thought to have been involved in planning the bomb attacks on the US embassies in east Africa in 1998 - and a close associate of bin Laden.
Some sources in the region say he is thought to have made trips outside of Iran in recent years. There have been media reports suggesting Adel wants to return to his home country of Egypt, but the former U.S. counter-terrorism official said even with the new leadership in Egypt, Adel might want to think twice about going there.
"Adel is a dangerous guy. He would not be accorded a warm welcome from Egypt and the U.S. would put a lot of pressure on Egypt," the former official said.
Venturing outside the relative safety of Iran has shown to be to be risky.
Osama bin Laden's son is believed to have left Iran in 2009 only to be killed shortly afterward in Pakistan. And now, bin Laden's son-in-law, Sulaiman Abu Ghaith, finds himself in U.S. custody.
Prosecutors say Abu Ghaith conspired to kill Americans as part of al Qaeda, according to a federal indictment. Through his attorney, the Kuwaiti pleaded not guilty to the charges in a federal courtroom in New York on Friday, nearly a week after his arrest.
After the attacks on New York and Washington in 2001, Abu Ghaith served as al Qaeda's official spokesman.
Prosecutors said he provided a 22-page statement to U.S. authorities after his capture, but officials didn't characterize its contents.
The former counterterrorism official said Abu Ghaith probably has plenty of information on al Qaeda in Iran, but doubts he has much knowledge of the overall organization.
"Al Qaeda is very compartmentalized and (Abu) Ghaith is not an operational guy," the former official said. "He's a propagandist."
CNN's Jamie Crawford and Tim Lister contributed to this report.