Tuesday was the day many insiders watching the Meredith Kercher murder trial had been waiting for. In the heart of Florence, inside a vaulted-ceiling courtroom with a giant crucifix, a three-judge panel was to finally rule on abuse-of-power charges against Giuliano Mignini and Michele Giuttari. These stem from the so-called Monster of Florence case, which inspired a bestselling book in the United States that has been optioned for the screen by Tom Cruise.

How, Knox’s supporters asked, could a prosecutor under investigation for misconduct be allowed to lead one of the country’s most notorious murder trials?

Mignini is the lead prosecutor in the murder case against Seattle native Amanda Knox and her one-time boyfriend, Rafaelle Sollecito, whose supporters have repeatedly alleged that Mignini is crazy and corrupt. Giuttari is the former head of the Florentine police force, and is now Italy’s top crime novelist. Among his seven thrillers is A Death in Florence, based on a serial killer who stalked the Florentine hills from 1968 to 1985 murdering and mutilating lovers parked in secluded spots.

The crux of the misconduct charges against the two men is that Mignini, the investigating magistrate, gave Police Chief Giuttari inappropriate assistance by ordering up a criminal analysis that should properly have been requested and paid for by the police. This transpired during the investigation of Francesco Narducci, a Perugian doctor who mysteriously floated to the surface of Lake Trasimeno in 1985 and who became Mignini’s prime suspect in the Monster killings. But after hours of deliberation, the verdict for Mignini and Giuttari was postponed. The presiding judge asked to hear four more witnesses to clarify various points about the investigation. The next court date is set for September.

The case has been closely watched in both Italy and the United States. American supporters of Amanda Knox were hoping for a guilty verdict to validate their conviction that Mignini is a rogue prosecutor; many Italians were hoping a not-guilty verdict would vindicate their judicial system. Neither side got their wish.

In Knox’s hometown of Seattle, there has been a steady drumbeat of outrage about Mignini—how, Knox's supporters asked, could a prosecutor under investigation for misconduct be allowed to lead one of the country’s most notorious murder trials? But the Mignini case is not necessarily anomalous. In reality, active prosecutors are often under investigation in Italy. Unlike in the United States, even the most banal accusations against anyone in power usually leads to trial here, clogging the country’s courtrooms with tedious disputes that cast a negative light on the entire judicial system. Italian prosecutors and investigators have less leeway than their American counterparts, so bending the rules is often part of criminal investigations. Earlier this year, Mignini was cleared of other charges against him, including wiretapping journalists.

The Monster of Florence case is better known, however, because it inspired a bestselling book in the U.S. and Mignini had an ugly run-in with the author, Douglas Preston. In 2006, Preston was called into Mignini’s office in Perugia while he was working with local journalist Mario Spezi on a true-crime account of the Florence murders, based on Spezi’s years’ covering the case, which he chronicled in an Italian book titled Dolci Colline di Sangue ( Sweet Bloody Hills). Tom Cruise, who later optioned Preston’s book, is rumored to be eyeing the role of Spezi, who became the indisputable expert on the Monster case.

Spezi will be the star of the movie, no doubt, but whether he will be cast as a hero or villain in real life is still up to the courts. Local authorities in Perugia say they long suspected him of manipulating evidence in the case, and Preston got caught up in their investigation into Spezi. In a bizarre intercepted phone conversation between Spezi and Preston, the two seem to discuss whether or not the police have “made their rounds,” which lead investigators to assume they had planted evidence to bolster their theory of the crime. Spezi was jailed for 23 days on suspicion of planting evidence. Preston was called into Mignini’s office for a two-plus-hour interrogation that the two describe very differently.

Preston says it was a terrifying moment that started out cordially but ended with Preston worrying that, “I could easily spend the rest of my life in an Italian prison.” Preston also says that Mignini ordered him to leave Italy. Mignini says that he never asked Preston to leave the country, but instead suggested that Preston didn’t understand Italian and that he should get a lawyer. Another witness to the meeting, a court assistant, backs up Mignini’s version, as does the curiously condensed transcript.

Preston’s description of his run-in with Mignini appears in both the first edition of Monster of Florence and the just-released paperback, and it has had a major impact on Americans’ views about the prosecution of Amanda Knox, even though the two cases are completely unrelated. In the latest edition of his book, Preston—who has not been in Perugia for the trial—has even added an afterword about the Kecher murder.

In the afterword, Preston writes that Mignini relies on a Roman psychic named Gabriella Carlizzi, who advises him on satanic sects—a point denied by both Carlizzi and Mignini, although they do admit knowing each other. (In fact, Mignini has charged Carlizzi with defamation on more than one occasion.) At one point in the investigation of Narducci in the Monster case, the prosecutors considered a satanic cult angle, and the investigators in Perugia initially suggested that Kercher might have been murdered in a satanic ritual because the murder occurred just after Halloween. But that theory has long been purged from the dossier and has played no part in the prosecution’s case against Knox.

The afterword also refers to a mysterious man covered in blood who was heard screaming “I killed her” the morning after Kercher’s murder. On June 23, though, witnesses in Perugia clarified this point for the jury in the Kercher murder trial, testifying that the man was embroiled in a lovers’ spat and was screaming into his cellphone “I will kill the bitch.”

Spezi is still under investigation in Perugia on a number of charges relating to the Monster of Florence case. Last spring, a local court denied his request for compensation for false imprisonment and refused to throw out the pending charges, which range from planting evidence to defamation. Preston is not considered a suspect but may be called as a witness if Spezi’s case goes to trial. Spezi says Mignini is out to get him because he and Preston have a different theory about who the real Monster of Florence is. The case remains unsolved.

Mignini in turn believes that Spezi is behind the abuse of power accusations for the same reason. “Those who think this case against me is justified are the same people who think the case against Knox is not,” Mignini said after the hearing. “Let’s let the courts decide who is right.”

Barbie Latza Nadeau has reported from Italy for Newsweek since 1997. She also writes for CNN Traveller, Budget Travel magazine and Frommer's.