(CBS) President Bush said Tuesday a "full-scale manhunt" was under way for al Qaeda operatives following the capture of suspected terrorist Jose Padilla.

"There's ... a full-scale manhunt on," Mr. Bush told reporters at the White House. "We will run down every lead, every hint."

Padilla, a 33-year-old U.S. citizen also known as Abdullah al Muhajir, was detained by the FBI in Chicago on May 8, when he arrived from Pakistan. He was held without charge until being declared an "enemy combatant" on Sunday, after which he was transferred to a naval brig in South Carolina, officials said.

Military officials have not decided whether to charge him or what charges to file, said Pentagon spokesman Lt. Col. Rivers Johnson.

"Padilla's where he needs to be," Mr. Bush said.

Attorney General John Ashcroft and other U.S. officials said Padilla was allegedly plotting to detonate a radioactive "dirty" bomb in the U.S., probably in Washington D.C.

But CBS News Correspondent Jim Stewart reports some U.S. officials now admit they're not sure what Padilla's plans were when he returned to the U.S. last month. And any plot, including possibly exploding a radiation bomb in Washington D.C., was in the "initial planning stages."

But given what Padilla had trained for in Afghanistan, they expected the worst.

"He researched nuclear weapons and received training in wiring explosives while in Pakistan, and he was instructed to return to the United States to conduct reconnaissance operations for al Qaeda," said Deputy Defense Secretary Paul Wolfowitz.

Investigators had known of Padilla for some time, including his alias. Much of their information about him came from Abu Zubaydah – al Qaeda's top surviving operations officer until his capture last March – who tipped them off to Padilla's American mission.

"He had indicated some knowledge of Washington, D.C., but I want to emphasize again that there was not an actual plan. We stopped this man in the initial planning stages," said Wolfowitz. That was echoed by FBI Director Robert Mueller, who also said the plan to explode a dirty bomb had not gotten past the planning stages.

Authorities described Padilla, born in New York and raised in Chicago, as a former Chicaco gang member who was brought up a Catholic but converted to Islam.

Commenting on Tuesday, Ashcroft said the suspect was involved in "very serious terrorist plots."

Speaking from Hungary, the latest stop on his overseas trip to discuss worldwide anti-terrorism efforts, Ashcroft described Padilla as a key al Qaeda operative who has "very significant information" on other terror suspects.

Officials said Padilla traveled to Pakistan and Afghanistan in 2001 and met with senior al Qaeda officials to discuss the plan.

The officials would not say whether the meetings took place before or after the Sept. 11 attacks on New York and Washington that killed 3,000 people and which the United States has blamed on Saudi-born dissident Osama bin Laden and his al Qaeda network.

U.S. officials knew Padilla was on the airplane heading into Chicago O'Hare International Airport on May 8, where he was detained upon arrival.

Mueller, whose bureau has been under fire for failing to share information with other U.S. intelligence agencies that might have prevented the hijacked airliner attacks, said the CIA played a key role leading up to the arrest.

After a 1991 arrest in South Florida on a handgun-related charges, Padilla began referring to himself as Abdullah al Muhajir, officials said. He lived in South Florida's Broward County from 1990 to 1997 and was convicted of aggravated assault with a firearm in Sunrise in 1992.

When he was arrested, he told police he had worked at a Holiday Inn in Plantation setting up banquet rooms for two weeks. Records show he has his name "Jose" tattooed on his right arm.

While in the Broward County Jail, he was accused of battery on a jail officer and resisting without violence in January 1992.

Padilla was last in the United States in 1998. After that he traveled mostly in the Middle East, officials said.

He is being held by the Defense Department as an enemy combatant, which under the rules of war allows him to be questioned without the usual protections afforded in the U.S. judicial system, like having an attorney present. Officials have not ruled out lodging criminal charges against Padilla later.

Mr. Bush has said American citizens would not be tried in military tribunals that were created after Sept. 11 to try foreign terrorists outside the U.S. court system.

Padilla becomes the third U.S. citizen detained since the Sept. 11 attacks. John Walker Lindh, 21, who was arrested in Afghanistan, faces charges in U.S. court in Virginia of conspiring to murder Americans and providing services to the Taliban and al Qaeda. The other is Yasser Essam Hamdi, 22, an American-born prisoner who was transferred from Guantanamo to a prison at Norfolk Naval Station in Virginia.