For more on new developments in the case against an American exchange student, watch CNN's "Murder Abroad: The Amanda Knox Story," at 10 p.m. ET Friday on CNN.
(CNN) -- Crime author Doug Preston admits that at first, he thought Amanda Knox was guilty of murdering her British roommate in what Italian prosecutors said was a sexual misadventure gone awry.
The best-selling author and journalist had seen his fair share of crime scene photos and police reports in his day. He'd even experienced the Italian justice system firsthand while researching Italy's infamous unsolved serial killings for his non-fiction book, "The Monster of Florence."
From what little Preston knew about Meredith Kercher's death in the Perugia apartment she shared with Knox, it seemed to him an "open and shut" case.
Then, he heard the name Giuliano Mignini, the assistant prosecutor leading the case against the University of Washington student studying abroad.
Preston met Mignini in 2004, when the prosecutor questioned him in connection with the "Monster of Florence," a case involving the gruesome murders of eight couples between 1968 and 1985. Preston said the encounter spooked him to the point that he decided to leave the country out of fear that he falsely might be implicated in the grisly murders.
The case also left its mark on Mignini, who was convicted and received a 16-month suspended sentence for abusing his office over law enforcement tactics - such as the wiretapping of offices -- in the "Monster of Florence" investigation. Mignini is appealing the conviction, but the allegations were still fresh when he was assigned to Knox's case in 2007.
Knox and her boyfriend, Raffaele Sollecito, were convicted in 2009 of murdering Kercher and sentenced to prison. But many, including Preston and Knox's family, believe the case was flawed from the start by shoddy police work, sloppy evidence handling and a prosecutor under pressure to secure a conviction.
Knox has appealed her sentence based in part on the forensic evidence used to convict her.
A court ordered retesting earlier in 2011 of a knife found in Sollecito's apartment with Knox's DNA on the handle and Kercher's DNA on the blade, Perugia prosecutors said. The sample, however, was so small that forensic scientists investigating Kercher's murder were not able to double test it in accordance with international forensic science norms, which Knox's legal team says raises doubts about its validity.
The forensic experts revealed their findings Wednesday, saying that while they agreed Knox's DNA was present on the knife handle, tests for Kercher's DNA were unreliable.
"There is no conclusive scientific evidence regarding the nature of the blood," forensic professors Carla Vecchiotti and Stefano Conti said in a 146-page report.
The second piece of evidence under scrutiny is a metal clasp from Kercher's bra. Forensic scientists in the investigatory phase determined that Sollecito's DNA was present on the metal clasp. But the clasp was not collected until nearly six weeks later, prompting Knox's defense to question whether the sample may have been contaminated.
The forensic experts agreed in part, saying that investigators did not follow "international inspection procedures and protocols for gathering and presenting evidence" in testing either the knife or the bra fastening.
Mignini insists that the evidence led to Knox and Sollecito, and that a just verdict was reached.
"My conscience is clear because I did what I believed I had to do. That was my conclusion," he told CNN. "When a magistrate asks for a guilty verdict, he does not do it cheerfully, quite the reverse. Because they are two young people. I see their families, their suffering and I realize. But I do it because it is my duty to do it."
The Perugia public prosecutor's office built a case against Knox and Sollecito based on several other factors, Mignini said. Knox's odd behavior -- public displays of affection between her and her boyfriend, which were caught on camera, while investigators searched her home -- didn't sit well with Mignini or Italy's court of public opinion. A "clouchard," or homeless heroin addict, said he saw the couple near the apartment the night of the murder. Furthermore, a window in the villa was broken, in what prosecutors interpreted as an attempt to fake a robbery.
There was the DNA evidence and Knox's written confession, in which she said she was in the home that night and falsely implicated as the killer her boss, Patrick Lumumba, who was later exonerated.
Italy's highest court eventually deemed the statement inadmissible in the couple's criminal trial, but left room for it to be used in a successful defamation claim brought by Lumumba against Knox. The two trials ran concurrently, and the confession was eventually heard in the civil case by the same jury that convicted Knox in the criminal case.
The DNA of another man, Rudy Guede, was found in the room and on Kercher's body. He admitted to being in the villa when Kercher was killed but said an unknown assailant killed her while he was out of the room. He was convicted in 2008 and sentenced to 30 years. An appeals court ruling cut that down to 16 years.
Knox and Sollecito were convicted in 2009 in a trial separate from Guede's. Knox was sentenced to 26 years in prison. Sollecito was sentenced to 25 years. But questions about the quality of the evidence linger among the pair's supporters.
'I had fallen into one of my own books'
Preston also thought the evidence against Knox and Sollecito seemed overwhelming. Then, he remembered his own encounter with Italian law enforcement.
He had once been interrogated as part of a murder investigation in Perugia, by none other than Mignini himself. The subject of the inquiry? The so-called "Monster of Florence," the topic Preston was investigating for his book.
"I felt like I had fallen into one of my own books. Now the funny thing is, I'd written many interrogations in my books -- you know, I write thrillers where people get interrogated -- I had never understood how brutal, psychologically brutal, an interrogation is. You feel absolutely helpless," he said.
Following the discovery of Kercher's body, Knox was interrogated by police but not by Mignini. Still Preston says the parallels between his interrogation and hers are stunning.
In the days following the incident, Knox went to the police station voluntarily several times to give statements as a witness, or in the parlance of the Italian system, a "person informed of the facts." In the early morning of November 6, four days after Kercher's death, Knox said police subjected her to a hostile interrogation over 14 hours at the police station. She claimed investigators struck her and yelled at her, denied her food or water, and caused her to make incriminating statements.
Since Knox was only a witness at the time, the interview was conducted without an attorney and was not recorded. It was conducted in Italian, though Knox had only been studying the language for two months. Knox said a translator was not present, though Mignini disputes this claim. At the end, she signed a statement in Italian saying she saw Kercher enter her room with Lumumba.
'Imagine' what would have happened
Knox said any apparent admission to being at the scene was made when investigators told her to imagine what she might have seen if she had been there. She later recanted the statement and the higher court ruled it inadmissible in the criminal trial because the statement was made without an attorney present.
Mignini arrived at the end of the interview. He and police denied Knox was mistreated or forced into making incriminating statements. He also disputed Knox's claim that the interview lasted 14 hours and that she was not given a translator. (In proceedings separate from the murder trial, Knox was ordered to stand trial for allegedly slandering police in connection with her claims about what happened during the interview. The proceedings were adjourned until November.)
Moreover, he said that as soon as she placed herself at the scene, she went from being a person informed of the facts to a suspect, and the interview was halted because she did not have an attorney.
"I remember two things about how she seemed, two things struck me. First, it seemed as if she had got a weight off her chest. Secondly, it was if she was terrified of Lumumba, he said. "She was crying with relief, that was her attitude."
Knox, Sollecito and Lumumba were immediately arrested and authorities publicly declared the case was solved.
But, it turned out, Lumumba had solid proof he was at his bar all night and was eventually cleared in the case. About that time, crime scene evidence led police to Rudy Guede.
But Knox's fate was already sealed, Mignini said.
"She placed herself at the scene of the crime and Lumumba wasn't there. but Rudy was, according to what emerged later. So, this fact of having accused, in a slanderous manner, Lumumba, is a very important element from the point of view of her position in the case," he said. "Why did she place herself at the scene of the crime? But she also placed another person there, someone who was absolutely not involved. Why? It is a very significant detail."
Crime author turned subject of interrogation
To Preston, it sounds suspicious, and all too familiar.
He had moved to Italy in August 2000 in search of inspiration for the perfect thriller. Instead, he found a true crime story more outrageous than any work of fiction he could dream up.
"The Monster of Florence" turned out to be a damning assault on the investigation into the gruesome murders of eight couples in Tuscany between 1968 and 1985.
The victims were all young lovers engaging in sexual acts, mostly in cars, in the hills above Florence. The killer would sneak up on the couple and shoot them, always with the same .22 Beretta, before mutilating the women and removing their genitals.
Preston and Italian journalist Mario Spezi essentially re-investigated the killings, going over crime scenes and reviewing FBI profiles drawn up at the request of Italian authorities. After their research, they believed they knew who the killer was -- someone who'd never been arrested by Italian police.
Over the years, police made seven arrests, according to Preston and other reports on the killings, only to learn that the killer was still out there.
When authorities were unable to find the lone killer whom crime scene analysts said was responsible for the killings, they came up with a theory involving a satanic cult.
After that didn't pan out, Preston says they set their sights on new targets: him and Spezi.
In 2004, Preston says, Spezi appeared on an Italian television show similar to "America's Most Wanted" and criticized the investigation. Later that year, Italian police raided Spezi's home, confiscating notes and computer files except for a floppy disc that he stuffed into his underwear, Preston said.
Soon thereafter, Preston said he received a phone call from police and later, a summons to appear in Perguia to speak with Mignini, the public minister of the region. He said he was told he had a right to a lawyer but that because he was not a suspect he did not need one. When he showed up to Mignini's office, Preston said he asked for a translator but was told it would take hours, and proceeded without one.
He didn't expect to be there long, but he said he ended up staying for two hours.
The conversation started out cordial enough, he said. Eventually, the questions became more and more pointed. They began recording the conversation while a stenographer wrote down everything he said.
"They'd read it back to me, 'Is this your answer?' And I'd say, 'No, that isn't quite what I said.' And then I'd have to rephrase it," he said. "And at a certain point I realized to my absolute horror that they were narrowing down on me as if I were a criminal and had committed a crime and that they were trying to trap me into confessing."
He asked Mignini if he was, in fact, a suspect to a crime.
"That's when Mignini said, 'Yes. We don't think it. We know it. We know you have committed a crime. We have the proof. And you are going to confess to it," Preston said.
According to Preston, the prosecutor laid out everything he was supposedly guilty of.
"They have techniques that could get you to confess to murder. I am not kidding. One of the techniques that they used on me was to ask me to speculate. 'Oh, well, if Mario didn't commit the murder... why don't you tell us, if he had committed the murder -- let's just assume that he had -- can you speculate how he might have done it? Can you speculate this? Can you speculate that? Tell us what you think.' And they get you speculating."
Preston said he did not sign the statement in Italian that was written for him. Neither he nor Spezi were charged with a crime, but he still thought it best to leave the country in February 2006.
Mignini disputed Preston's version of events. For one, he says the interview lasted less than two hours. Mignini also said he stopped Preston's interview when evidence of a crime surfaced and told him he needed to get a lawyer.
He also claims Preston signed the statement that was written for him.
"I challenged some of the things he said and I remember that I let him listen to recordings of some of the telephone interceptions that were made, calls in which he spoke to Spezi, and what he said was not credible," he said.
"I made the statement, because I had to dictate the statement to my assistant who had to write it down. Preston signed it and so he acknowledged the truth of the statement, because he signed it, he didn't refuse to sign it."
Leaks early on in the Knox case from the prosecutor's office emphasized theories of a sex game gone awry and the possible involvement of a satanic cult. Mignini's theory of the case still involves a sex game gone awry, but he denied the theory of a satanic cult was ever considered or that his office was the source of those statements.
Prosecutors labeled Knox and her boyfriend the killers and a jury ultimately agreed. But Preston and Knox's supporters maintain that the theory of the crime was made to fit around Knox and Sollecito, based on thin forensic evidence, regardless of the fact they had Guede -- the person whose DNA was found inside Kercher's body.
"To save face... because they had made this public declaration of guilt of this American and her boyfriend, they had to retroactively link her and her boyfriend to this real killer and claim that all three did it," Preston said.