Playing Tricks with the Fort Dix Six?

"Now you see why we were going to sacrifice all for the sake of allah in jihad," says the neatly handwritten note on prison-issue paper. "We weren't able to finish."

Those seemingly incriminating words are part of a letter the U.S. Attorney's office in New Jersey says one of the defendants in the "Fort Dix Six" homegrown terror case wrote to a fellow inmate at the Federal Detention Center (FDC) in Philadelphia. It was allegedly written by Eljvir Duka, who is charged with conspiring to attack the Fort Dix military base with automatic weapons. He and four other young Muslim men who grew up in the South Jersey area have all pleaded not guilty, and the trial is set for March. The jihad letter appears, at first glance, to be a damning piece of evidence against Duka.

But a TIME investigation of the Fort Dix Six shows that little in this case is as it first appears. While carefully assembled by authorities, who collected hundreds of hours of video and audio evidence, the case is built almost entirely on the work of a paid informant with a criminal record. More and more terrorism cases are being constructed this way, and the problematic role of informants doesn't stop after the arrests are made, as this latest plot twist reveals.

Now a professional handwriting analysis of the letter commissioned by TIME casts serious doubt on its authenticity. The jihad letter was allegedly sent by Duka to another Muslim inmate in the 1,201-person detention center. To back up the allegation, the government recently released an eerie prison surveillance video showing a piece of paper sliding along the floor from one cell to the next in the Federal Detention Center.

The two inmates had struck up a correspondence, in violation of jail rules, and the other inmate had asked Duka to write him a prayer. A week later, that same other inmate wrote a note to a guard explaining that he had decided to turn in a letter he claimed Duka had written. He did it, he wrote, in hopes that he could help the authorities and in turn help himself. He did not specify what he wanted. (The inmate is incarcerated for violating his parole after a previous assault conviction.) Duka denied that he had ever written the note, and insisted, through his attorney, that it was not his handwriting.

To find out if Duka wrote the letter, TIME asked two respected document examiners to compare the inflammatory letter to four other letters Duka had written his attorney and the judge.

Handwriting analysis can be very useful — or worthless, depending on the methods of the examiner. To ensure a reliable analysis, TIME arranged for two kinds of assessments: one by a computer program written by Sargur Srihari, the director of the Center of Excellence for Document Analysis and Recognition at the State University of New York (SUNY) at Buffalo; and another, more traditional human analysis by John Hargett III, who was the chief document examiner for the Secret Service for 11 years before going into private practice.

Both examiners found that Duka's writing in the sample letters does not match the writing in the note. "There is an abundance of significant, basic differences in letter formations and writing habits," Hargett concluded. For example, in Duka's actual letters to his lawyer, Duka generally connects the letter "r" to the letters following it. In the disputed letter, the "r's" remain detached. The "p's" and the "a's" are also quite different in the two letters, Hargett notes. Both examiners also felt that the writing in the jihad letter did not match the writing of the inmate who had turned the letter in. But the available sample of the other inmate's writing was far too limited to form a reliable conclusion.

The government is conducting its own analysis of the documents, but it has not made its findings public. In a December 2007 court filing, the prosecutor did, however, publicly accuse Duka of writing the letter, citing the letter's "violent nature" as one reason Duka should continue to be held in a segregated housing unit at the Federal Detention Center. When told about TIME's findings, a spokesperson for the U.S. Attorney's office, J. Gregory Reinert, declined to comment. "We cannot comment on evidence in the case, particularly as we near trial," he wrote via email.

Duka's attorney, Troy Archie, says he was not surprised by the results of TIME's analysis. "I knew my client didn't write this. It's so obvious," he says. He also is not surprised that another inmate may be trying to set his client up. "This happens all the time at the FDC in Philly. They call that place a rat's nest."

Of the five main defendants, Duka is the most religious, according to Archie. In response to the inmate's request, Duka did indeed send a written prayer, Archie says. That is what is being passed between cells on the prison video, Archie says. But he says that prayer is not what the other inmate handed over to authorities.

This kind of convoluted back-and-forth is common in prison; inmates do communicate, even when they are not supposed to. And it's fairly routine for inmates to turn over — and sometimes even invent — damning material in hopes of getting some kind of deal. The risk of other inmates "jumping on a case," as it is known in prison parlance, is particularly great in high-profile ones like the Fort Dix case. "I told these guys from Day 1, 'You're going to be targets. Don't talk to anybody," says Michael Huff, attorney for Dritan Duka, Eljvir's older brother and another defendant in the case. "But it's easier said than done. It's tough to isolate yourself from the rest of the world."

The mystery letter will likely be further debated when the case goes to trial later this year. Until then, says Huff, "We're having to defend against the government — and against other inmates."