The trial is ready to begin. Amanda Knox says because she's been staying in prison, she doesn't grasp that to Italians she's become a pariah, the presumptuous, promiscuous American. In court, everyone... See More
The trial is ready to begin. Amanda Knox says because she's been staying in prison, she doesn't grasp that to Italians she's become a pariah, the presumptuous, promiscuous American. In court, everyone sees her at times smiling, at times stoic, other times not seeming to pay attention. Once wearing a t-shirt from the beatles song, "All you need is love." It was another one of my naive immaturity. I didn't realize how very intensely I was being scrutinized. You thought you were going to be acquitted? How could I be convicted? That's what I was thinking. But the prosecutor, mignini, is ready with his case, arguing what happened that night was a sex game, targeting Meredith and spiraling out of control. Police have created a kind of avatar cartoon for the trial, showing how Amanda Knox might have wielded a knife, while Raffaele held Meredith down. Mignini argues they could have been on drugs like cocaine, though police did not do a drug test. And then, mignini produces a murder weapon, a knife taken from Raffaele's kitchen drawer, which Knox says they used for cooking. But mignini says it has Meredith's DNA on the blade and Amanda's on the handle. Later, independent experts will say a credible lab would be skeptical about identifying DNA from such a small sample. And that other speck on the blade is rye bread. Next, they produce a small piece of Meredith Kercher's bra clasp, claiming that it bears Raffaele's DNA. But one problem, they admit the police accidentally left the clasp at the crime scene for 47 days, only discovering it in a different place on the floor. In police video, you can see them passing it around, dirt on their gloves, raising questions of contamination. And among the prosecution witnesses, the star would be this man, Rudy guide. He was known to perugian police as a thief, a drug user, who had threatened people with a knife. He fled perugia the day after the murder. A friend got him on tape saying he'd been at the house that night, but just going to the bathroom, and Amanda Knox wasn't there. But a year later, his story had changed. He says he did see her through a window. But here's the issue at the center of the trial and the question of reasonable doubt. Rudy guede's DNA is everywhere in Meredith's room, on her purse, where her cell phones and money are missing. The bloody shoeprint they once said was Raffaele's, was his. And the handprint matched his exactly. Also inside Meredith's naked body, Rudy guede's DNA. So, how can police explain the fact that at the crime scene there is not one trace of DNA from Amanda Knox. The prosecutors will say she must have cleaned hers off. It's impossible to see DNA, much less identify whose DNA it is. The trial will continue for 318 days. On December 5, 2009, two years after the murder, Amanda Knox is called back into the courtroom and hears the word colpevole. Guilty? Colpevole. And it was a roar in the courtroom. People exclaiming. My mom and my sister crying. And I couldn't breathe. Everything that I thought I knew about the way justice and life worked was gone. Outside, Italians rejoice. Amanda Knox was found guilty. As the verdict was read Amanda Knox and her family began to sob. Her sense 26 yesentence /- her sentence, years in prison. Capanne prison, 500 prisoners. In a tiny room, a 22-year-old American girl sentenced to 26 years has only a small window onto a cypress tree. She says day and night she could hear women wailing in their cells. You wrote, "I felt as if I were being sealed into a tomb." Yeah. And the tomb was my life. It wasn't the prison. It was my life. Did you think about suicide? I did. She writes she considered cutting her wrists in the shower or swallowing bleach. She says she had panic attacks, began to lose her hair. And one day a doctor called her to say he had more bad news. They had analyzed the blood sample from the day she arrived. And the doctor told me that I had tested positive for HIV. I was stunned. And then, incredibly, they tell Knox it was all just a mistake. She was not hiv-positive at all. She writes that what will save her in prison are small acts of humanity. A cellmate from America. She was great. We would sing "The star-spangled banner" every morning. And most saving of all, someone still in her life today, the chaplain of the prison, don Saulo, who taught her this prayer. God, if you exist, I really need you to help right now. I didn't have that same faith. But he convinced me that it wouldn't hurt to pray that if there's a god, to please help because, because we're all helpless. As her lawyers began filing appeals court briefs, she says she began searching for a purpose. Studying Italian literature. Living for the days her family could come. They have mortgaged homes, traveled 6,000 miles to be near her. Parents, stepparents, aunts, uncles, friends. I saw them 1% of the time. And yet, they were always there. They were there 100% of the time. Did you think what it was costing them spiritually? Actually? I felt incredibly guilty for what they were having to sacrifice for me. And there was a certain point in my, in my thinking in prison that if it didn't work out and I never was free again, I was trying to figure out how I could ask them to move on with their life without me because I was tired of them having to sacrifice everything for me. Everything. After 1,427 days, the appeals court is about to render a new verdict. In her now-fluent Italian, she talks about Meredith. And then October 3, 2011, the appeals court judge issues a scathing criticism of that first trial. He cites the "Dubious reliability of a key witness, the non-existence of the prosecution evidence" and a motive he said prosecutors couldn't prove. Ammanda Knox is finally acquitted and goes free. Outside, Italians, outraged at her acquittal, jeer, "Shame, shame."
This transcript has been automatically generated and may not be 100% accurate.