Atta in the middle

An al-Qaida plot to blow up the U.S. Embassy in Rome. Another to set terrorist commandos loose in Strasbourg, home of the European Parliament. A third to spirit a suicide bomber into the American embassy in Paris.

Authorities on both sides of the Atlantic have described the plots as the work of a highly compartmentalized organization whose members often weren't aware of each others' activities.

Even so, a look reveals that many of those suspected of orchestrating terror against Americans had direct and frequent connections -- a meeting in Spain, a phone number found in Hamburg, a London cleric who was a religious inspiration to terrorists in different cells.

And connected to it all, Mohamed Atta -- the suicide pilot Osama bin Laden described as "in charge of the group" of Sept. 11 suicide hijackers -- seems to have been the common thread that wove through the lives of many bin Laden agents.

Atta's travels in the last months of his life brought him in contact with some of those allegedly behind plots against the U.S. embassies in Rome and Paris, as well as a cell officials say was plotting to attack the European Parliament and other targets in Strasbourg, France. He also met an Iraqi intelligence official in Prague and is suspected of links to a group of North Africans in Spain that authorities say was planning to attack U.S. interests in Europe.

While the other al-Qaida plots in Europe were thwarted, the one Atta controlled directly -- leading a team of suicide hijackers who threw their lives away in order to take thousands more -- succeeded.

U.S. authorities, who spoke on condition of anonymity, say they have placed Atta at the center of their investigation and are working backward, retracing his steps in order to reach other potential terrorists.

The Rome plot

When the U.S. Embassy in Rome went on alert and shut down for three days last January, there was a suggestion al-Qaida may have been plotting an attack.

Four months later, Italian police nabbed Essid Ben Khemais, a burly Tunisian known as "the Saber." Italian prosecutor Stefano Dambruoso has said Ben Khemais was sent from Afghanistan to supervise bin Laden's terrorist operations in Europe. He is considered a high-ranking bin Laden associate who Spanish officials say met with Atta in Spain weeks before his arrest.

Italian investigators have said they've uncovered evidence of cooperation among al-Qaida cells in Germany, France, Spain and Belgium.

Under Ben Khemais' direction, the investigators say, an Italian-German cell plotted to bring down the heavily guarded U.S. Embassy, a 19th century building on Rome's fashionable Via Veneto. Two members of the cell were arrested shortly after the Sept. 11 attacks, including a Tunisian man picked up outside a Milan mosque referred to by the State Department as al-Qaida's "main station house in Europe."

Some time between the closing of the Rome embassy and Ben Khemais' arrest in April he met with Atta in Spain, Spanish police say. What the men discussed is not known.

The Hamburg cell

The Dec. 11 U.S. indictment of Zacarias Moussaoui, a French citizen of Moroccan descent arrested in Minnesota three weeks before the Sept. 11 attacks, shed more light on the cell Atta operated in Hamburg, Germany.

U.S. authorities allege that Moussaoui, who authorities say would have been among the hijackers had he not been arrested, followed many of the same patterns as the 19 hijackers, all of whom were named as unindicted co-conspirators along with bin Laden.

The indictment also linked Moussaoui to Ramzi Binalshibh, an alleged member of the German cell who once lived with Atta in a Hamburg apartment where they are believed to have planned the Sept. 11 attack.

U.S. investigators believe Binalshibh was meant to have been the 20th hijacker and have suggested that Moussaoui may have been picked as an alternate when Binalshibh was denied entry into the United States.

Atta's ties to Binalshibh and hijacker Marwan al-Shehhi go back years. The three worked together between 1997 and 1998 at a company outside Hamburg called Hay Computing Service GmbH, company officials said.

In October 1999, Atta and Binalshibh both attended the wedding of Said Bahaji, a 26-year-old German-Moroccan who vanished shortly before Sept. 11 and is thought to have been part of the Hamburg cell.

At Bahaji's wedding, a lavish affair at a local mosque, at least three of the hijackers and their cohorts bumped shoulders with members of Hamburg's Muslim community, including a Syrian-born import-exporter named Mamoun Darkazanli.

The Bush administration has accused Darkazanli of operating a front for al-Qaida, and Spain has named him in the indictment of Sept. 11 suspect Imad Yarkas, who comes from Darkazanli's home town of Aleppo, Syria. Atta also spent time in Aleppo during the mid-1990s while researching his dissertation on trade development there.

Despite the ties, German authorities have said they don't have enough evidence to arrest Darkazanli.

The recruiters

Spanish authorities would like to know why Yarkas' Madrid phone number appeared in an address book found in Atta's Hamburg apartment after the attacks.

Did Atta meet the man suspected of recruiting and fund-raising for al-Qaida during one of his Spanish trips? Investigators can't say.

What the Spanish Interior Ministry has said is that Yarkas, who used the alias Abu Dahdah, was the "representative of the organization run by Osama bin Laden in Spain," and spent years hiring holy warriors and raising an undetermined amount of cash to pay for their operations.

On Nov. 18, Yarkas and seven others were charged in a Madrid court with belonging to al-Qaida. Baltasar Garzon, Spain's top anti-terrorism judge, said they "were directly linked to the preparation and carrying out of the attacks perpetrated by suicide pilots on Sept. 11, 2001."