MIAMI - A covert CIA officer who was permitted to testify wearing a disguise and using an alias described in court yesterday how U.S. officials in Afghanistan obtained a truckload of al-Qaeda documents, including a form later linked to suspected operative Jose Padilla.

The officer, whose true identity is classified, gave his name as Tom Langston. He appeared in court with a beard and glasses, though the nature of the disguise was not obvious or made public. Prosecutors declined to say whether any concealment was even used.

Langston testified that he was working in December 2001 at a classified CIA site in Kandahar, Afghanistan, when an Afghan man driving a pickup truck showed up with thousands of pages of documents.

Among them was a blue binder containing what appeared to be dozens of forms in Arabic, one of which reportedly turned out to be Padilla's. Prosecutors say his fingerprints are on the "mujahedeen data form," which asked about language skills, military experience, religious education and other areas.

The form is crucial to the government's case because it could link Padilla and codefendants Adham Amin Hassoun and Kifah Wael Jayyousi to al-Qaeda. They are charged with being part of a U.S.-based support cell for Islamic extremists.

The unidentified Afghan man, Langston said, was affiliated with an Afghan tribal leader opposed to the country's Islamic fundamentalist Taliban rulers, who were then battling U.S. forces. Under the Taliban, al-Qaeda had established terrorist training camps in Afghanistan in the years leading to the Sept. 11, 2001, terrorist attacks.

The Afghan man told the CIA he collected the documents from a house occupied by Arabs who had fled shortly before the 2001 U.S. invasion and were known locally to be affiliated with al-Qaeda. Langston said the man was not paid or given any other benefit by U.S. officials for the documents.

"I think he took this initiative on his own," the CIA officer said of the man.

The binder and other documents were kept in a locked room at the CIA installation in Kandahar, then taken on U.S. vehicles and aircraft to the FBI in Islamabad, Pakistan.

It wasn't until later that the FBI in Washington was able to link one of the forms to Padilla, who allegedly filled it out under the name Abu Abdullah al-Mujahir in July 2000. A key to making that link was information gathered during U.S. interrogations of other suspected al-Qaeda figures, according to documents filed in the Padilla case.

Testimony will resume tomorrow. Prosecutors say their witnesses will include Yahya Goba, a member of the "Lackawanna Six" who pleaded guilty in 2003 in New York to attending al-Qaeda camps. Goba, who received a 10-year prison sentence, will testify that he attended the same camp as Padilla and filled out an identical form, prosecutor Brian Frazier said.

Padilla, 36, a U.S. citizen and former Chicago gang member, was arrested in 2002. The administration initially accused him of plotting to detonate a radioactive "dirty bomb" in a U.S. city, but those allegations are not part of the criminal indictment. He was added to the Miami case after being held for 31/2 years in military custody as an enemy combatant.