(CBS) John Walker Lindh and other al Qaeda and Taliban prisoners told U.S. interrogators the Sept. 11 hijackings were supposed to be the first of three increasingly severe attacks against Americans. Their claims have not been corroborated, government officials said.

Lindh will be sentenced Friday, likely to 20 years in prison, for supplying services to the Taliban and carrying an explosive during commission of a felony. He heard some of the claims while serving in a 20-man Taliban infantry unit of Arabic speakers in Afghanistan, according to people familiar with his account.

Authorities have gathered similar information from prisoners of various levels of the terrorist network. But the officials said the United States hasn't found specific plans for two additional large-scale attacks and they suspect the claims could involve disinformation or folklore that circulated among low-level terrorists and Taliban soldiers after Sept. 11.

"We have not been able to corroborate the claims among the thousands of pages of documents and other evidence we have gathered the last year," one senior law enforcement official said. "We believe some of these prisoners may have been trained to give misinformation or simply were passing on rumors."

One law enforcement official said some al Qaeda and Taliban prisoners said the second and third wave attacks could involve biological, chemical or radiological weapons to increase casualties and were designed to paralyze Americans with fear and cripple the economy.

Details of Lindh's extensive interrogation, part of his plea agreement, remain secret. However Rohan Gunaratna, a terrorism expert who worked with defense lawyers and interviewed Lindh, said the California native told him he picked up battlefield rumors about two waves of post-Sept. 11 attacks.

Another individual familiar with Lindh's interview by Gunaratna, who asked not to be identified by name, said Lindh also said he heard the latter two attacks were supposed to be severe enough to make Americans forget about Sept. 11.

Gunaratna spoke with Lindh in his jail cell for eight hours on July 25-26 as a defense consultant, and submitted a report to a federal judge that concluded Lindh never swore loyalty to Osama bin Laden and al Qaeda.

Still, Gunaratna said, Lindh would be a valuable U.S. intelligence asset because he understood what makes Islamic fundamentalists join conflicts around the world.

The terrorism expert said he believed from the interviews that Taliban soldiers heard talk of hitting "infrastructure targets" in the post-Sept. 11 attacks, in addition to rumors of an unconventional weapon.

Gunaratna said he understood from Lindh that the fighters believed unconventional meant a biological agent. However, Gunaratna said he believes intelligence information available elsewhere indicates the weapon could be a radiological device, a so-called "dirty bomb."

Lindh also said he heard that 50 people were going on 20 suicide missions, but added he received the information on the front lines in October — not prior to Sept. 11 when at a training camp, as his original indictment indicated.

Officials have had indications that additional attacks may have been planned immediately after Sept. 11.

For instance, shortly after the jetliner crashed into the Pentagon, German intelligence intercepted a phone call originating in the United States suggesting other terror teams were on the ground and ready to strike, U.S. and foreign intelligence officials say.

Officials said prisoners from the war on terrorism, including some kept at Guantanamo Bay, Cuba, have given similar accounts about two more attacks that were supposed to follow Sept. 11.

The details of the prisoners' account vary widely, officials said, but most agree that the subsequent attacks were supposed to be more severe than the Sept. 11 attacks that leveled the World Trade Center, damaged the Pentagon, crashed a plane in Pennsylvania and killed more than 3,000.

Lindh, 21, pleaded guilty July 15. He was captured last December with other Taliban in Afghanistan, the last stop on his journey from a teenage convert to Islam in San Francisco's suburbs to a foot soldier for the vanquished Afghan regime.

If the new revelations come up during Lindh's sentencing on Friday, his lawyers can take the tactic that even last December Lindh was cooperating with authorities, says CBSNews.com Legal Analyst Andrew Cohen.

As they prepare for their final court hearing on behalf of an unpopular client, Lindh's attorneys continued to remind the judge and the public that "Mr. Lindh is not a convicted terrorist, nor does he pose a threat of terrorist violence"; that he "has fully and forthrightly accepted responsibility for his actions"; and that he "has provided and continues to provide full cooperation with the United States government in ongoing investigations."

And if they were to answer the last-minute leak by the feds, they'd probably remind the judge and the American people that the information Lindh gave last December, before he was even charged, showed even that he was willing to cooperate with his fellow countrymen. Also, that, in the written words of one interrogator, he "showed remorse and signs of regret." What better proof, the defense would argue, than that John Walker Lindh today regrets what he did and wants to help make it right, says Cohen.