Washington ? The man accused of plotting with al-Qaida to detonate a “dirty bomb” inside the United States was a protege of a top lieutenant of Osama bin Laden, traveling at his mentor’s request to meet with other terrorists and using the Internet to research how to build a radioactive weapon, U.S. officials said Tuesday.

Jose Padilla, 31, also known as Abdullah al Muhajir, traveled to Pakistan and Afghanistan to meet with top al-Qaida leaders after the Sept. 11 terror attacks and surfed the Internet at a home in Lahore, Pakistan, to study ways to build a “dirty bomb” that could spread radioactive material over dozens of city blocks, officials said, speaking on condition of anonymity.

Padilla

But Padilla’s alleged association with Abu Zubaydah, the top lieutenant to bin Laden who was captured in March, was his apparent undoing.

Information leading to Padilla’s arrest came in part from Zubaydah himself. In April, weeks after Zubaydah’s arrest, he told interrogators of a plot to use radiological weapons, but he did not provide details. The CIA investigated and came up with Padilla’s name and other details.

That information including Padilla’s name was taken to Zubaydah, who confirmed it. It’s unclear whether Zubaydah volunteered the information or was tricked into giving it.

Watched and arrested

Padilla apparently lost his passport in Karachi, Pakistan, in February and sought a new one, State Department spokesman Richard Boucher said Tuesday. The government complied in March but tipped off the FBI and CIA about Padilla’s location and his request.

Padilla traveled May 8 to Chicago from Pakistan via Cairo, Egypt, and Zurich, Switzerland, a U.S. official said Tuesday.

Padilla had $10,000 in cash on him when he was arrested, a government official said Tuesday, speaking on condition of anonymity. Officials suspect Padilla got the cash from al-Qaida, possibly while he was in Switzerland, the official said.

President Bush, who signed the order Sunday handing over Padilla to the Pentagon, described Padilla as one of many “would-be killers” in custody by the United States.

“There’s just a full-scale manhunt on,” Bush said Tuesday. “We will run down every lead, every hint. This guy Padilla’s a bad guy and he is where he needs to be, detained.”

A military policeman stands guard at a North Charleston, S.C., gate of the Charleston Naval Weapons Station. Jose Padilla, also known as Abdullah al Muhajir, who is accused of plotting with al-Qaida terrorists to detonate a dirty

Later, visiting Missouri, Bush said: “We’ve rounded up and detained over 2,400 terrorists, and that’s good. … The number’s now 2,401.”

Defense Secretary Donald Rumsfeld said the government was more interested in questioning Padilla than punishing him.

“We’re not interested in punishing him at the moment,” Rumsfeld said, traveling in Qatar. “We’re interested in finding out what in the world he knows. … Our job as responsible government officials is to do everything possible to find out what that person knows and see if we can’t help our country or other countries.”

Legal maneuvers

Fresh details emerged Tuesday about why U.S. authorities chose to permit Padilla to slip aboard an international flight from Pakistan into Chicago, under constant surveillance by U.S. agents on the jet. The FBI arrested Padilla on May 8 after he stepped off the plane.

In an unusual legal twist, the Defense Department has imprisoned Padilla indefinitely in a Navy brig in South Carolina as an “enemy combatant.” Government lawyers acknowledged Tuesday that under a 1942 Supreme Court ruling, even Americans who fight against the United States are subject to military courts but only if they enter the country. The court’s decision, from six decades ago, focused on “armed prowlers” who blow up bridges or cut telegraph wires.

The Bush administration disclosed Padilla’s arrest on Monday, just before a federal court hearing in New York to determine whether the Justice Department could continue holding Padilla behind bars as a material witness connected to the government’s grand jury investigation into the Sept. 11 attacks.

At Tuesday’s court hearing, the judge hinted that any question about the propriety of prosecutors’ holding Padilla was a moot point since he already had been turned over to the Defense Department.

Arguing for rights

Donna Newman, Padilla’s lawyer, said outside court later that Padilla denied the government’s allegations, but she otherwise declined to describe him. She indicated that she will appeal the decision to place Padilla in military custody, but in such a novel case there were unanswered questions about where she even could file her appeal in New York or South Carolina?

“His response is the allegations are not true because there are no allegations. He’s not been charged, but he’s being detained,” Newman said.

“My client is a citizen,” she added. “He still has constitutional rights the right to counsel, the right to be charged by a grand jury. … And they have not charged him.”

Padilla is not considered a prisoner of war or entitled to legal protections under the Geneva Convention, unlike the U.S. treatment of uniformed, enemy soldiers, government lawyers said.