A DEADLY PUZZLE

Tanweer also traveled to Pakistan in 2003 and again at the start of this year. Pakistani authorities believe he made contact with militants, including the outlawed Kashmiri independence groups Lashkar-i-Taiba and Jaish-i-Mohammed. Investigators say he also spent time at a madrassa near the city of Lahore, although they deny knowing whether the religious school has any jihadist ties. Six Pakistanis were detained last week in connection with the investigation. (The officials add that they have no record of Hussain's visit.) The Pakistanis claim that a tip from them fueled Operation Crevice, based on information found on the computer of Al Qaeda's alleged Webmaster in Lahore, Muhammed Neem Noor Khan, after his arrest a year ago. They also claim that this past May they gave London another warning about possible attacks after the capture and interrogation of senior Qaeda leader Abu Faraj al-Libbi near Peshawar. But a U.S. government official says that al-Libbi did not give interrogators specific information about this month's plot.

The hunt for one or more masterminds in the subway attacks has led to North Africa as well. British authorities issued a worldwide alert for Magdy Mahmoud Mustafa el-Nashar, 33, an Egyptian chemist at Leeds University who had not been seen on campus since early July. Investigators emphasized that he was wanted for questioning, not as a suspect. His rented home in the city's Hyde Park area is two blocks from a house that was described by police as a "bomb factory." A bathtub at the latter residence reportedly contained evidence of the dangerously unstable explosive TATP, the same stuff the Qaeda "shoe bomber" Richard Reid was wearing on his feet when fellow passengers prevented him from blowing up an airliner three days before Christmas 2001. A substantial quantity of the same explosive was discovered in a rental car that had been abandoned at the Luton railway station, near Aylesbury, on July 7.

Late last week the Egyptian government confirmed that Nashar had been arrested. He was just leaving afternoon prayers at the Tawhid mosque near his parents' home in Maadi, a Cairo suburb, when three police cars pulled to a stop. "Two men got out of one of the cars and went right for Magdy," says Ahmad Gamal, a 13-year-old family friend who watched it happen. "They took him into the car, and the others told everyone to keep walking." The chemist furiously protested his innocence, and Egypt's Interior minister categorically denied press speculation that Nashar had ties to Al Qaeda. In the United States, FBI agents visited North Carolina State University and served a subpoena on Peter Kilpatrick, head of the school's chemical- and biomolecular-engineering department, who handed over all available records pertaining to Nashar's brief stint as a chemical-engineering student there in early 2000.

Some U.S. and British officials suspect that the plot may have involved several facilitators, possibly a recruiter based inside the country and an operations expert from elsewhere who paid occasional visits to the bombers. The facts that have been uncovered so far suggest that the four were carefully screened and indoctrinated. Some townspeople, including Khan's family, said the young men had been "brainwashed"--but by whom? Leeds residents say the city's mosques are relatively moderate and decidedly nonviolent. Some neighbors point to the bookshop on Bude Street, while others blame militants who have gravitated to the nearby Hamara youth center, an interfaith meeting place created in 1995 by a consortium of two churches, a mosque and four other community groups.

Last Thursday the inhabitants of Beeston joined the rest of the country in two minutes of silence to honor the bombers' victims. The brief commemoration had barely ended when sirens pierced the stillness. Police motorcycles and bomb-disposal specialists roared down Lodge Lane to a building formerly used by the youth center. Police evacuated the area for several blocks around before setting off a controlled explosion and sending in a radio-guided robot. The center's director, Hanif Malik, denied that the bombers had any official part in administering its services. He confirmed only that the three men sometimes used the center's gym facilities.

Deep beneath the streets of London, workers continued to sift through the wreckage. British authorities warned that unraveling the plot was likely to take months, if not longer, and they begged the public for patience. Some individuals clearly weren't listening. Mosques across Britain received bomb threats last week, and racist Web sites called for a campaign of violence against Muslims. Jihadists could only rub their hands at the thought.

WITH ZAHID HUSSAIN IN ISLAMABAD; EMILY FLYNN, CARLA POWER AND STRYKER MCGUIRE IN LONDON; GAMEELA ISMAIL AND DAN EPHRON IN CAIRO, AND ED CARAM IN RALEIGH, N.C.,GRAPHIC BY JOHN SPARKS AND H. LEE WHACK JR.

© 2005