The sheikh was a devout Muslim whose lifelong ambition was caring for the poor in Yemen, one of the world's most underdeveloped nations. Yet now he needed help himself. His health was deteriorating, and no facilities in his country were sophisticated enough to treat him.
So he turned to his new friend, "Yussef," a wealthy but disillusioned young African-American. Yussef had converted to Islam and traveled to Yemen to become more devout, like the now infamous John Walker Lindh.
The young convert suggested a trip to Germany, where the sheikh could both visit experienced doctors and raise money for his causes.
But Yussef wasn't the person he seemed. As an American undercover agent, he was trying to trap the Muslim leader, who is alleged by the US to be a key financier of terrorism. What followed is a tale of deception, betrayal, and intrigue - and of the clashing international interests and viewpoints that make the pursuit of terrorists so complex.
The fallout has created a behind-the-scenes rift between the US and two of its key partners in the war on terror - Germany and Yemen. Germany is now holding the sheikh and his personal secretary. But both the US and Yemen want them, for different reasons.
A German court must rule on the disposition of the men by mid-March - a decision that is likely to have a crucial impact on how well Germany and Yemen work with the US in the future. Both countries have provided essential intelligence and assistance in tracking down Al Qaeda members worldwide.
But both countries also have domestic populations increasingly at odds with US foreign policy, which is complicating the Yemeni case and shows the difficult politics of conducting any global dragnet on terrorism.
"There is a lot more under way operationally, and American patience is much less than it once was," says Daniel Benjamin, an expert on terrorism at the Center for Strategic and International Studies in Washington. "This kind of operation gets people very exercised, and it demonstrates just how freighted these operations have become."
In the mid-1990s, Sheikh Mohammed Ali Hassan al-Mouyad founded the Al Ehsan Mosque and Community Center in the dusty outskirts of Sana, Yemen's capital. The center feeds about 9,000 families a day, and provides free educational and medical care as well. Besides his work with the poor, the sheikh also serves as a consultant to Yemen's Ministry of Endowments and is a top leader in the opposition Islamic party, Al-Islah.
But it was at the mosque and community center where Yussef turned up. By demonstrating his dedication to the cause of furthering Islam, he eventually became a confidant of Sheikh Mouyad, according to foreign intelligence sources.
It was Yussef who suggested the sheikh travel to Germany, where he would receive the most advanced treatment for asthma and diabetes, and gain something even more valuable: Yussef would introduce the sheikh to an "investor" who would make a handsome donation to the sheikh's charity to help care for the poor - and, he assumed, to help finance terrorist attacks.
The young American took prodigious care of all the arrangements. In early January, Sheikh Mouyad and his personal secretary, Mohammed Moshen Yahya Zayed, flew to Frankfurt, where Yussef had arranged for a room at the airport's Sheraton Hotel. He also organized transportation - a black Mercedes in which to travel to and from their appointments.
But Yussef provided more than met the sheikh's eye. Hidden cameras and speakers were embedded in both the Sheraton hotel room and the Mercedes, and Yussef was "wired," according to officials familiar with the case. All the conversations among the sheikh, Yussef, and the investor concerning the transfer of money for alleged nefarious activities - including meetings in the hotel and a Frankfurt restaurant - were recorded.
On the evening of Jan. 9, the men sealed their deal in Mouyad's Sheraton hotel room with a handshake. The investor agreed to provide $25 million to the sheikh's charity the next day for both humanitarian assistance and for terrorist attacks to be carried out by the Palestinian Hamas and Al Qaeda network, foreign officials say. The sheikh was also to provide the bank account numbers to expedite the wire transfer.
But when the appointed hour arrived for Yussef and the investor to show up on Jan. 10, a switch was made. When the sheikh answered the knock at the door, the German federal police, and FBI agents, acting on a tip from the CIA, arrested the two men and whisked them away by helicopter to the Wellerstadt prison outside Frankfurt.
They are still being held there - pending extradition to the US - for providing material support to the Al Qaeda terrorist network. The US alleges that the sheikh is an associate of Abdul Raham al-Nashiri, who is a top Al Qaeda member charged with planning suicide bombings, including the October 2000 attack on the USS Cole in Yemen, in which 17 servicemen died. Al Nashiri was picked up - on a tip from Yemeni authorities - by the CIA at an airport in the United Arab Emirates in November.
A spokesman at the US Department of Justice says that, "because of law-enforcement sensitivities, the agency does not comment on extradition requests between countries." Nor would the CIA and FBI publicly comment on the case.
Germany, for its part, claims it is providing all the legal assistance it can to the US. But in order to turn these men over, German authorities say they must have evidence a crime was committed that is punishable in both Germany and the US - the country seeking extradition. But so far, they say, the evidence is inconclusive.
"We have nothing against them," says a German official. "When we act on a tip-off, our legal system starts to work. It's at the court in Frankfurt, where it will be resolved by mid-March."
On a recent visit to the US, Germany's intelligence chief admonished US Attorney General John Ashcroft to come up with better evidence - and soon, according to one official who attended the meeting. Germany, the official asserts, is becoming increasingly vexed with the case the US has so far presented. And the official says that Germany feels placed in a very precarious position - between the US and Yemen.
The German official says relations between Germany and Yemen in general have become so tenuous that Germany has temporarily canceled Lufthansa flights to Yemen and is warning its citizens not to travel there because of possible retaliatory strikes.
Yemeni officials, for their part, claim they were not told in advance about the plan to arrest the sheikh, and don't understand why.
"The arrests were a total surprise to us," says Abdulwahab al-Hajjri, Yemen's ambassador to the US. "We are asking the Germans to give them back to us, because we want to make sure they have something on them." Besides, he adds, "who better to interrogate them than their own countrymen who know the language, the culture?"
Ambassador Hajjri also says the sheikh is a prominent figure in Yemen, and the arrest is causing a backlash among a population already not happy with the country's cooperation with the US on the war on terror. "It sends a wrong signal to our population, which sometimes now believes we are cooperating with the US and other times we are not," he says. "And now they don't know if they can believe us about Sheikh Mouyad, who is very well loved and respected in Yemen."
Since the 2000 attack on the USS Cole in the port of Aden, Yemen has cooperated more fully in the US fight on terror. That attack, Hajjri says, was also an attack on the economic interests of the Yemen government.
Since then, the Yemeni government has helped the CIA and FBI track down terrorists affiliated with Al Qaeda. In November, for example, they participated with the CIA in a missile attack that killed six alleged terrorists.
That's been followed by a number of smaller-scale, retaliatory attacks on Yemeni government officials. And in early December, a French oil tanker was bombed off the coast, in the same way the Cole was attacked. Later in December, three US missionaries and a Yemeni official were killed by radical Islamists.