A computer specialist arrested this week in England possessed the classified routes of a U.S. naval battle group and is part of an al Qaeda branch linked to Sept. 11 mastermind Khalid Sheik Mohammed that authorities on three continents have been working to dismantle in recent weeks, according to court documents released yesterday and U.S. officials.

Babar Ahmad, who possessed three-year-old documents detailing the routes and vulnerabilities of the USS Constellation, which was then operating in the Straits of Hormuz, is the cousin of Muhammad Naeem Noor Khan, a key figure in the recent arrests of alleged terrorist plotters, U.S. intelligence officials said.

Khan became part of a sting operation organized by the CIA after he was captured last month and agreed to send coded e-mail messages to al Qaeda contacts around the world, according to a senior U.S. official. U.S. authorities are using the information to identify other operatives.

Khan's arrest led to the discovery of computer equipment containing detailed pre-Sept. 11, 2001, surveillance of five U.S. financial buildings that caused U.S. officials to raise the threat alert level for the financial sectors in Washington, New York City and Newark.

"We believe there were direct and indirect connections between Khan and individuals we believe are involved in the pre-election threat" to sites in the United States, said the senior U.S. official, who asked not to be identified further. The official declined to give any more details about the link.

Khan was arrested after the June apprehension of Abu Musab al Baluchi, a nephew of Khalid Sheik Mohammed, who oversaw the Sept. 11 attacks.

The unraveling of a network with direct links to Mohammed and the computer equipment and Internet connections discovered in the process are a valuable catch that has given U.S. and foreign intelligence and law enforcement officials dozens of new leads, officials said.

The computerized data from Ahmad's arrest alone -- 500 gigabytes -- resulted from nine search warrants and 100 subpoenas, said Michael J. Garcia, the assistant secretary of homeland security in charge of the Bureau of Immigration and Customs Enforcement. Department of Homeland Security investigators are poring over the data -- the equivalent of 10 hard drives from moderately priced home computers -- for clues to other al Qaeda suspects, plots and Web sites.

Ahmad, who according to the court documents operated two U.S.-based Web sites to recruit and raise money for Taliban fighters, had been under investigation for three years, Garcia said. He is in London, and the United States is seeking to extradite him to face charges here.

Another law enforcement official said Ahmad's arrest on Wednesday and the extradition request were hastened after the apprehension of 12 men in England on Tuesday. They include Eisa Hindi, described as a significant al Qaeda figure in Britain who helped prepare the pre-Sept. 11 surveillance of the five U.S. financial buildings.

One of the men, the official said, had computerized information connected to Ahmad.

Ahmad, 30, a British subject of Pakistani descent, faces four charges of involvement with terrorism, each with a penalty of 10 years to life in prison, according to the criminal complaint unsealed yesterday by the U.S. attorney's office in New Haven, Conn., where Ahmad's Web site servers were based.

Ahmad appeared for the first time in a British court yesterday. Rosemary Fernandes, appearing for the U.S. government, said Ahmad had documents outlining the specific assignments of each ship, a drawing of the battle group's formations and details of its movements on April 29, 2001. The classified documents also noted that ships in the group could be vulnerable to a small craft firing rocket-propelled grenades, she said.

Ahmad's attorney denied he was involved in terrorism, and his sister told a Muslim news service in London that the charges were "all lies." Ahmad told the court he opposed extradition to the United States. A magistrate agreed to hold him pending another hearing next Friday.

The U.S. extradition request accused Ahmad of operating a series of "pro-jihad" Web sites, including two that appealed to Muslims to use every possible means to undertake military and physical training for holy war. The sites also appealed for financial support and provided instructions on how to infiltrate war zones in Afghanistan and Chechnya.

Ahmad, who lives in south London and works at Imperial College there, was arrested by British police last December and held for six days under suspicion of terrorism. At that time, Fernandes told the court, investigators searching his house found the naval documents, which suggested planning for an attack similar to that carried out against the USS Cole in Yemen in 2000.

Fernandes said Ahmad was in contact with an unnamed al Qaeda agent who worked within the battle group.

U.S. naval officials identified the man as a reservist who is no longer in the military service. A Navy spokesman said the man could not be tied "directly to the information," one reason he has not been charged with any crime.

Ahmad's attorney described his client as an educated professional who had lived in Britain all his life and had no prior criminal record. She alleged that Ahmad had been assaulted by police both in his home and in a police van during the December arrest and search.

"The police searched everything in December last year," Ahmad's sister, who would not disclose her name, told Muslim News. "They took away his computers, private mail. . . . They did not find anything then." She added: "There is no proof of his involvement in terrorism."

Contested extradition requests can take five years or longer to work their way through British courts, although Home Secretary David Blunkett, who oversees such requests, has pledged to streamline the process. Blunkett issued a statement Friday evening through the British Press Association seeking to reassure the public after reports that five al Qaeda militants were at large.

He said the authorities were "taking every feasible precautionary measure to protect British citizens both here and abroad."

The wave of arrests was reportedly triggered by the June 12 capture of Abu Musab al Baluchi, nephew of Khalid Sheik Mohammed and a cousin of Ramzi Yousef, who organized the 1993 bombing of the World Trade Center. Baluchi was previously identified by Pakistani authorities as Mussad Aruchi.

Baluchi's arrest led to the capture in Pakistan of Khan, 25, a computer engineer, and Ahmed Kahlfan Gailani, a Tanzanian. Khan was a frequent visitor to Britain, and officials at City University in London have confirmed that he enrolled there last year, although he dropped out after a few weeks.

The charges against Ahmad are similar to charges the federal government pursued unsuccessfully this spring against a Saudi doctoral student at the University of Idaho. Sami Omar Hussayen was acquitted of allegations he sought to provide material support for terrorists by running an Internet network that sought to raise money and recruit fighters for holy war in Chechnya and Palestine. Hussayen argued that his maintenance of Islamic Web sites was constitutionally protected free speech.

But Hussayen's Islamway Web site offered some scholarly material as well as support for jihad, while the sites that Ahmad administered -- www.azzam.com and www.qoqaz.net -- were described by a Justice Department official as "more operational."

The court documents indicate that Ahmad allegedly worked with a New Brunswick, N.J., man who made backup copies of the site.

Frankel reported from London. Staff writer Susan Schmidt and researcher Robert Thomason contributed to this report.

British police escort relatives of Babar Ahmad from a London court after a hearing on charges that Ahmad recruited and raised support for the Taliban.