A covert CIA officer permitted to testify wearing a disguise and using an alias described in court Tuesday how U.S. officials in Afghanistan obtained a truckload of Al Qaeda documents, including a form later linked to alleged 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, although the nature of the disguise was not obvious or made public. Prosecutors declined to say if any concealment was even used.

The arrangement was approved by U.S. District Judge Marcia Cooke at the request of the CIA, which sought to protect the officer's ability to continue doing clandestine work overseas. It was not disclosed to the jury.

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 bright blue binder containing what appeared to be dozens of forms in Arabic, one of which allegedly turned out to be Padilla's. Prosecutors say his fingerprints are on the "mujahedeen data form," which had questions on language skills, military experience, religious education and other areas.

The form is crucial to the government's case because it could link Padilla and his two alleged co-conspirators — Adham Amin Hassoun and Kifah Wael Jayyousi — to Al Qaeda. The three are charged with being part of a U.S.-based support cell for Islamic extremists around the world, including Al Qaeda.

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.

"He was loyal to some individuals who were cooperating with us against the Taliban and the terrorist element," the CIA officer said.

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, although he was prohibited after prosecutors objected from answering questions about whether the man's tribal leader was compensated.

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

At one point, Langston grew reluctant to answer a question from Padilla attorney Orlando do Campo about how CIA officers and analysts handle documents such as those in the binder.

"I'm a little uncomfortable answering the question because it gets into methods. I'm sworn to protect sources and methods," he said.

The binder and other documents were kept in a locked room at the CIA installation in Kandahar, then placed in boxes and transported on U.S. vehicles and aircraft to the FBI in Islamabad, Pakistan. The binder was in a box labeled "vegetable oil," the CIA officer said.

The FBI legal attache there in late 2001, Jennifer Keenan, testified Tuesday that she remembered the binder among 22 boxes, trunks and other containers because it appeared to hold information important for U.S. counterterrorism investigators.

"We were very grateful to find this," Keenan said. "I called it a pledge form. It says pledge on it."

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 alleged Al Qaeda figures, according to documents filed in the Padilla case.

Padilla, a 36-year-old former Chicago gang member and U.S. citizen, was arrested by the FBI in May 2002 when he arrived at Chicago's O'Hare International Airport. The Bush 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.

Padilla was added to the Miami case after 3 1/2 years in military custody as an enemy combatant. His case was the subject of a lengthy legal battle over the president's wartime detention powers over U.S. citizens.

Padilla and his two co-defendants face up to life in prison if convicted on all charges.