MIAMI - A key piece of evidence in the case against terrorism-support suspect Jose Padilla came from an Afghan who told the CIA he had found it in an al-Qaeda safe house, according to new court filings.

The man, unknown to the CIA at the time, drove up to the agency's installation in Kandahar, Afghanistan, in a pickup truck containing "stacks of papers and other office materials" found in the house occupied by a group of Arabs, according to a CIA document newly filed in federal court.

It was common knowledge, the man said, "that the Arabs residing in this home/office, as with many other similar sites in the city of Kandahar, had been affiliated with al-Qaeda and Osama bin Laden," according to the CIA description of the December 2001 meeting.

The Arabs fled the house just before the U.S.-led invasion of Afghanistan that October, he said.

Among the Arabic documents was a blue binder containing dozens of forms that U.S. officials say were essentially applications for al-Qaeda training camps. One form was filled out and signed by Abu Abdullah al Mujahir, one of the aliases used by Padilla, according to federal prosecutors.

While the existence of the "mujahedeen data form" has long been public, how it wound up in U.S. hands had never been disclosed.

The document was filed last week, before the April 16 trial of Padilla and two codefendants on charges that they were part of a North American support cell for extremists worldwide.

Padilla, 36, a U.S. citizen, was held for 3 1/2 years as an enemy combatant once suspected of plotting to detonate a radioactive "dirty bomb" in this country. He was added in November 2005 to the Miami terrorism-support case, which does not mention a "dirty bomb" plot.

The form, which prosecutors say contains Padilla's fingerprints, is considered the government's single strongest piece of physical evidence. The CIA has asked that the officer who accepted it from the Afghan man be permitted to testify in disguise.

It is unclear whether any other people whose names are on the forms will be called to testify. Defense lawyers say they anticipate testimony authenticating the forms from Yahya Goba, one of the "Lackawanna Six" group of men in Upstate New York who was convicted on terrorism-support charges for attending camps in Afghanistan.