Odyssey of an Al Qaeda Operative

Investigators said he also had an uncanny ability to change his appearance. Grainy mug shots of Mejjati released by the FBI show a dark-haired man with a scraggly beard. A wanted poster in Morocco portrays a completely different look: a thinner Mejjati wearing glasses and a red-and-white checkered kaffiyeh, or headdress, with a neatly trimmed mustache and no beard.

Mejjati drew fresh attention in Europe after the Madrid train bombings. Although investigators have not confirmed his presence in Spain, they said he worked closely with a suspected ringleader in the plot, another Moroccan named Amer Azizi, who has been indicted by Spanish officials but remains a fugitive.

The investigators said Azizi and Mejjati trained together at militant camps in Afghanistan in the late 1990s and are considered top leaders of the Moroccan Islamic Combatant Group, which allegedly recruited many of the foot soldiers who carried out the attacks in Madrid.

Less than a month after the Madrid explosions, Mejjati's name surfaced again, this time in Belgium. Threatening e-mails sent to several newspapers in Antwerp on April 1, 2004, warned of pending attacks against Jewish targets in the city. The messages were unsigned but contained Mejjati's name in the text and suggested that he had inspired those making the threats.

Belgian authorities said at the time that they did not take the threats seriously, but they became more concerned a few months later when police in a town outside Antwerp arrested a suspected al Qaeda operative named Hussein Mohammed Haski. The arrest set off alarm bells throughout Europe because Haski was known by Moroccan and Saudi officials to be a follower of Mejjati.

Several months earlier, Mejjati and Haski, also a Moroccan, joined 24 others on Saudi Arabia's most wanted list, the only two who were not from the Arabian Peninsula. When Haski surfaced in Belgium, some European counterterrorism officials feared that Mejjati was trying to set up another sleeper cell, this time in their back yard.

The search for Mejjati then shifted to Europe, although some counterterrorism officials speculated that he had sought refuge in more remote areas, such as Pakistan, Iran or along the Syria-Iraq border.

But Saudi security forces last month unexpectedly came across him in the small town of Ar Rass, about 220 miles northwest of Riyadh. After receiving a tip that some militants were in the area, Saudi police surrounded a building and engaged in a fierce gun battle that lasted for three days, according to the Saudi Interior Ministry.

Saudi officials said they killed 15 militants and captured six others. Only after the shooting stopped did they discover that one of the dead was Mejjati. His teenage son, Adam, was also killed.

"He was so good that we had no idea what he was doing," said a Saudi security source who spoke on condition of anonymity. "We had no tangible evidence where he was. The thing we do know is how sophisticated he was and what he was able to set up, inside and outside the kingdom."

Staff writers Steve Coll in Jiddah, Saudi Arabia, and Dan Eggen in Washington, and special correspondent Maria Gabriella Bonetti in Paris contributed to this report.