An FBI informant testified Monday that a top Al Qaeda official lived in California's Central Valley in the years before the 2001 terrorist attacks, but the statements were attacked immediately as unreliable.

The testimony came during an ongoing terrorism-related trial involving a father and son from Lodi, an agricultural town about 35 miles south of Sacramento.

The government informant, Naseem Khan, testified that he often saw Ayman Al-Zawahiri, Usama bin Laden's physician and top deputy, attending a mosque in Lodi in 1998 and 1999. Khan was living there at the time.

"Every time I would go to the mosque, (Al-Zawahiri) would be coming or going," Khan testified, according to a story posted Monday on The Sacramento Bee's Web site. "He would quietly come to the mosque and leave."

Prosecutors offered the testimony to show why the FBI began investigating Lodi's Islamic community. The agency recruited Khan in December 2001, and he initially focused his undercover efforts on two Muslim clerics.

He soon began concentrating on 23-year-old Hamid Hayat, who sometimes worked seasonal jobs at a fruit-packing plant.

Hayat and his father, Umer, who drove an ice cream truck, have been charged with lying to federal investigators about the younger man's suspected attendance at an Al Qaeda terrorist training camp in Pakistan in 2003.

Khan's testimony was discounted immediately outside court by law enforcement officials, Lodi residents and defense attorneys representing the two men on trial.

"It's outrageous," said Wazhma Mojaddidi, Hamid Hayat's attorney. "He (al-Zawahri) never lived in Lodi."

Nasim Khan, no relation to the FBI informant, was the mosque's president from 1998 to 2000 and said al-Zawahri never attended. He and Mojaddidi both noted that al-Zawahri, an Egyptian, would have been noticed in the largely Pakistani community.

Al-Zawahiri is known to have traveled to the United States in the years before the terrorist attacks, as did members of the Taliban. Federal officials and news accounts say he passed through northern California on fundraising missions during the late 1980s and early 1990s, travels that included visits to mosques in the San Francisco Bay area, Stockton and Sacramento.

He may have lived in the Sacramento area for an undetermined period in or around 1995 while visiting area mosques, according to an FBI agent in Washington, D.C., who spoke Monday on condition he not be named.

After August 1998, U.S. authorities were aggressively seeking al-Zawahiri and bin Laden in connection with the U.S. Embassy bombings in Tanzania and Kenya that killed more than 200 people, including 12 Americans. Al-Zawahiri headed the Egyptian Islamic Jihad until it merged with bin Laden's Al Qaeda in 1998.

Naseem Khan, 32, was working in a convenience store in Bend, Ore., when he was recruited by the FBI.

He completed his testimony Monday against Hamid Hayat, who is charged with three counts of making false statements to the FBI about attending the camp and with providing material support to terrorists. He faces up to 39 years in prison if convicted on all counts.

Umer Hayat, 48, faces 16 years in prison if convicted of two counts of making false statements to FBI agents.

The Hayats are being tried before separate juries that are scheduled to be brought together for the first time Tuesday in U.S. District Court.