(CBS) Since December, when the government indicted Zacarias Moussaoui as the first man charged in the Sept. 11 attacks, an unusual gulf has opened between what prosecutors have charged in court and what investigators are saying privately about what they can prove about him, The New York Times reports.

Prosecutors have charged that Moussaoui played a direct role in the Sept. 11 hijackings, and some officials have said they believe he was supposed to be on one of the four planes. But investigators now say the evidence is not so clear, the Times reports. In fact, they say they believe he may been in the United States to take part in a different plot, the Times says.

That gap has opened wider in recent days with Moussaoui's rambling, combative and often confusing statements in court, according to the newspaper. He has declared his allegiance to al Qaeda and asserted that, if allowed to plead guilty, he would provide a grand jury with an authoritative insider's account of the hijacking plot — even though at other points he said he was not involved.

If the judge in his case, Leonie Brinkema, allows Moussaoui to plead guilty at a hearing scheduled for Thursday, Moussaoui would follow John Walker Lindh, the Taliban warrior, in short-circuiting the prosecution. If that happens, each case would have begun with broad assertions that were never proven in court, the Times points out.

Government officials say they have no direct evidence that Moussaoui had a role in the hijackings. From the beginning the evidence has been circumstantial. Now, some government officials, in interviews with the Times, are saying prosecutors overreached when they charged that Moussaoui was a direct participant with Osama bin Laden and al Qaeda in the conspiracy that killed thousands of people on Sept. 11.

With Attorney General John Ashcroft's counterterrorism team anxious to demonstrate its aggressive approach, federal prosecutors have dismissed the internal criticisms, telling the Times the case against Moussaoui is strong and that prosecutors had won convictions in jury trials with less evidence than they have against Moussaoui.

But Moussaoui's erratic recent performances in court proceedings have upset the Justice Department's effort to bring him to trial in an orderly legal process, the Times points out. Instead, Moussaoui has managed to raise even more doubts, not only about his emotional and mental competence to stand trial and act as his own lawyer, but also about whether someone with his apparent instabilities could provide a credible account of his own activities.

Government trial lawyers and F.B.I. agents often disagree about the weight of evidence in criminal cases, but usually it is the F.B.I. that is arguing for a tougher charge, the Times explains. In this case, some prosecutors have said that the F.B.I. has been especially eager to depict Mr. Moussaoui as a minor figure, in part, because the bureau hoped to dampen the controversy about whether it acted properly last summer, when it refused to seek a warrant to search Mr. Moussaoui's laptop computer. The computer was not searched until after the Sept. 11 attacks.

The government has yet to produce a witness against Moussaoui. What they do know is that he received a wire transfer from Ramzi bin al-Shibh, a Yemeni who, according to the indictment, acted as a financial conduit for the plot. In addition, Moussaoui's movements in the months before he was arrested were almost identical to those of the 19 hijackers.

But investigators have said they have failed to find evidence that Moussaoui ever met Mohamed Atta, the plot's ringleader, or any other hijacker — or that he communicated with any of them by e-mail, telephone or letter. Still, Moussaoui's associate, Hussein al-Attas, has told the authorities that Moussaoui had said it was acceptable to kill civilians who harmed Muslims.

Investigators have said they have no precise understanding of why Moussaoui entered the U.S., although they are convinced he was a Islamic militant who arrived to take part in some kind of terror operation. The investigators have speculated that whoever recruited him may have not told him anything about the operation he was to take part in, the Times explains.

Some officials still suspect that Moussaoui was meant to be the 20th hijacker on Sept. 11 and was recruited late in the plot when al-Shibh failed to obtain a visa to enter the U.S. If so, he would probably have been a fifth man on the hijack team that seized United Airlines Flight 93, which crashed in Pennsylvania with four hijackers on board; the other planes were commandeered by five hijackers. But this remains little more than suspicion.

Lately, some other investigators have come to suspect that Moussaoui might instead have been recruited for a different, still unknown, operation, speculating that the Sept. 11 hijack teams had already been selected before he entered the U.S. Because he had taken flight lessons and had information in his computer about crop-dusting aircraft, these investigators suspect that he was meant to take part in an attack involving one of those types of planes, the Times reports.

In his court appearance this week, Moussaoui's often ranting statements seemed to support that theory. He confessed that he was part of Al Qaeda, was loyal to bin Laden and had joined in terrorism conspiracies. But he repeated his claim that he had "no participation" in the Sept. 11 conspiracy.
Nonetheless, Moussaoui, who is acting as his own lawyer, has offered to testify before a federal grand jury to reveal what he knows about the Sept. 11 conspiracy and al Qaeda.

But prosecutors and the judge in the case have treated his offer with skepticism, especially given his initial demand — now dropped — that the appearance be televised and that he be accompanied into the jury room with a Muslim lawyer of his choosing.

Edward MacMahon, one of the team of court-appointed lawyers that Moussaoui has tried to fire, said in a Times interview that in the course of representing Moussaoui, the Justice Department had never approached the defense team with a request that Moussaoui submit to an interrogation or consider a plea bargain that would require his cooperation.

That, MacMahon said, suggested that the department understood that Moussaoui was a low-level conspirator who knew little, if anything, about the terrorist network.