Khalid Shaikh Mohammed, the suspected mastermind of the Sept. 11 terrorist attacks who may also have played a role in the murder of journalist Daniel Pearl, was believed to be in U.S. custody overseas Sunday.
Mohammed was arrested Saturday in a raid in the Pakistani city of Rawalpindi, near Islamabad.
The joint raid by CIA and Pakistani agents snared in addition to Mohammed an unidentified man of Middle Eastern origin and a Pakistani identified as Ahmed Abdul Qadoos, a 42-year-old member of one of the country's main religious parties, Jamaat-e-Islami.
The unidentified suspect was "proving to be an important man," a senior official said.
Mohammed's capture was a spectacular victory for the U.S.-led war on terrorism. Mohammed is the suspected mastermind of the Sept. 11 attacks and a senior operative in Usama bin Laden's Al Qaeda network.
The arrest of Mohammed and the two other men likely will hurt the terrorist organization's ability to launch more attacks and could provide the United States with new clues in the hunt for bin Laden.
"It's hard to overstate how significant this is," White House spokesman Ari Fleischer said. "It's a wonderful blow to inflict on Al Qaeda."
Mohammed, 37, is perhaps the most senior Al Qaeda member after bin Laden and his deputy, Ayman al-Zawahri.
A naturalized Pakistani who was born in Kuwait, Mohammed is on the FBI's most-wanted list and allegedly had a hand in many of Al Qaeda's most notorious attacks. The U.S. government had offered a reward of up to $25 million for information leading to his capture.
There also has been suspicion that Mohammed was involved in last year's kidnapping and murder of Wall Street Journal reporter Daniel Pearl, and may have even carried out his execution.
CIA officers and Pakistani authorities carried out the operation that led to Mohammed's arrest, according to American officials, who spoke on condition of anonymity. Mohammed is the third senior Al Qaeda figure to be arrested in Pakistan.
"This is a great success today, but the war on terrorism goes on tomorrow," said Jim Wilkinson, a spokesman at U.S. Central Command in Tampa, Florida. "There's still a lot of work to do."
U.S. officials say Mohammed organized the Sept. 11, 2001, terror mission that sent hijacked passenger jets crashing into the World Trade Center, the Pentagon and a field in Pennsylvania, killing more than 3,000 people.
But even before then, Mohammed was wanted in connection with plots in the Philippines to bomb trans-Pacific airliners and crash a plane into CIA headquarters. Those were broken up in 1995.
He also has been linked to April's bombing of a synagogue in Tunisia. At least 19 tourists, mostly Germans, were killed then.
Mohammed narrowly escaped capture in a raid about a week ago in the southwestern town of Quetta, a Pakistani government source said. During that raid, a Middle Eastern man, possibly of Egyptian origin, was arrested, according to the source, who spoke to The Associated Press on condition of anonymity.
"At the time of that raid in Quetta the authorities were looking for Khalid Shaikh but he escaped and from there they followed him to Rawalpindi," the official said. "They got information from the man they picked up in Quetta and from phone calls until they tracked him down to Rawalpindi."
Senior government officials said the three men were arrested about 3 a.m. local time Saturday at a house where Qadoos lives with his father.
But Omar Qadoos, Ahmed's cousin, said only Ahmed, his wife and two children were in the house. There also was a guard outside, he said.
"The police pounded on the gate and then they rushed through. There was some firing, but no one was hurt and then they beat the guard and broke the lock on the front door," Omar Qadoos said.
He said police held the family at gunpoint while they collected cassettes, a computer and computer discs, leaving the floor littered with clothes, papers and other items.
Mohammed's ties to terrorism are deep. He is the uncle of convicted 1993 World Trade Center conspirator Ramzi Yousef and one of his older brothers also belongs to Al Qaeda. Another brother died in Pakistan when a bomb he was making exploded.
He also is said to be close to bin Laden's son, Saad.
The Pakistani government says it has handed over more than 420 Al Qaeda and Taliban suspects to the United States.
Until now, the biggest catch so far was the arrest last March of the group's suspected financier, Abu Zubaydah, who was taken into custody in a raid in the central Pakistani city of Faisalabad. Abu Zubaydah, a Saudi-born Palestinian, was said to be a link between bin Laden and many of Al Qaeda's operational cells.
Abu Zubaydah ran the Khalden camp in Afghanistan, where U.S. investigators believe many of the Sept. 11 hijackers trained.
On Sept. 11, 2002, Ramzi Binalshibh, a would-be hijacker who could not get into the United States, was captured in the southern port city of Karachi. He was an aide to Mohammed and a key moneyman for the attacks.
Binalshibh also was the former roommate of hijacker Mohamed Atta.
The Associated Press contributed to this report.