You are looking at a surveillance camera in perugia italy as day turns into night. NOVEMBER 1st, 2007, 8:41 P.M. There is a small dot there, hard to see, something moving. In court they will say this... See More
You are looking at a surveillance camera in perugia italy as day turns into night. NOVEMBER 1st, 2007, 8:41 P.M. There is a small dot there, hard to see, something moving. In court they will say this is probably the last image of meredith kercher alive, heading toward her home about 100 feet away. She will be brutally attacked in her bedroom. And we warn you this police video is graphic. There are 47 cuts and bruises on her neck, legs, face, inside her mouth. Her clothes ripped off. And around her body etched in blood, a shoe print, a hand print on the wall, a footprint on the bathmat in the bathroom. Drops of blood on the faucet. Meredith kercher had studied karate. It's clear she fought hard for her life. A life filled with possibilities. This is her acting in a music video back home in england. She's studying politics in perugia, has lots of british friends. Six weeks before her death she meets her new roommate in the house, the american amannox. At was the first thing you thought when you saw meredith? I was putting away my things in the room when she came to my door and introduced herself and was immediately very nice. Just this -- this immediate exchange of, wow, this is -- this is someone who -- who I can get along with. Reporter: Knox says she and meredith and their two italian roommates beme easy friends, happy. Though at the trial meredith's friends will testify she was annoyed by amanda's loudness and lack of inhibition. Were you ever jealous of her? No. Reporter: Were you ever angry at her? No. Reporter: When we take a camera break, she's looking down. I ask what she's thinking. It bothers me when people suggest that she wasn't my friend. I was stunned by her death. She was my friend. Reporter: Amanda knox has now been in italy five weeks, going to school in the morning, working for a bar at night. And as far as her experiment with casual sexual encounters -- there have been two italian men. Then, she goes to a classical music concert and sees a young man who reminds her of harry potter. A graduate student in computer science. Nerdy, very inexperienced with girls, raffaelle sollecito says he can't believe the beautiful uninhibited american is looking at him. Colpe de fumine. Colpe de fumine. That's a lightning strike. Yeah, he writes about how taken he was with me. And I really liked him, as well. Reporter: They have known each other just 7 days before they enter the 24 hours at the center of this mystery and debate. THE NIGHT OF NOVEMBER 1st, WHEN Meredith kercher is murdered. Amanda knox says she and her new boyfriend have been spending nights at his apartment. What are you doing the night of NOVEMBER 1st? November 1st we stayed in, and we had dinner. We watched a movie. Reporter: His computer confirms that someone had ordered that movie, "amelie." A witness confirms she and raffaele were there in his apartment at 8:40 p.M. We smoked. We had sex. We were together. We just hung out together. We talked. He talked to me about his mom. We made faces at each other. We were being silly and togeth Reporter: She says in the college town of perugia, marijuana was as common as pasta. And mostly makes it her go and sleepy. How high were you? I'd smoked a joint with raffaele. And what that did to my memories was it made them less concrete. But it didn't black them out, and it didn't change them. Reporter: You remember with clarity that you did not go out that night? You stayed in the whole night? We stayed in the whole night. Reporter: The next morning it is undisputed that knox is the first person in the house where a murder has taken place. She says she made the five-minute walk from her boyfriends apartment to take a shower, get fresh clothes. She says she noticed the front door standing open, thought it was odd, but the latch didn't always work. And even though she saw some blood on the sink, she says she took the shower thinkingaybe meredith hadn't cleaned up. Or was it her own newly pierced ears? At the sink when I was taking out my earrings that I noticed that there were speckles of blood. But speckles. A few drops. Reporter: Did you see the bathmat? Did you see -- not yet. Reporter: The footprint -- not yet. I saw that when I was getting out of the shower. And I thought it was strange. Reporter: But you know people look at this and they say, door open, blood in the bathroom. Those are red alarms. Well, I had never before experienced anything in my life that was drastic. Reporter: People think you would be automatically concerned. Indeed, I was. That's why I called my mom. Reporter: She woke her mother in the middle of the night in seattle. Also phoned one of her roommates. But when she got back to raffaelle's apartment she didn't even mention what she had seen until after they'd had breakfast. She says still telling herself -- don't freak out because it could really be nothing. Reporter: She says, ultimately raffaelle will call police, and her roommate filomena is there when the door to meredith's bedroom is knocked down. Amanda knox phones her mother again, and says with her beginner's italian, she's trying to understand the torrent of words. And someone was screaming, "a foot." And I remember very distinctly telling her, because she was like, "what do you mean a foot? A foot? What does that mean? Is there -- wh and I said, I don't know. I don't understand. Then filomena was crying out, "meredith." And so I heard that it must be meredith. And that there was a body and that there was an armoire, and there was blood, and there was a blanket. Reporter: From this point on, amanda knox and her behavior will be a kind of kaleidoscope of shifting shapes depending on what you see. Is inappropriate behavior evidence of guilt? Or as she says, was she just a tone deaf girl in a trauma? She sits on raffaelle's lap at the police station, playfully making faces. She tells meredith's grieving friends that meredith must have suffered -- "she had her effing throat cut." Sorry about that now? I could have been more sensitive. Reporter: Not knowing police are studying her every move. A female officer later testifies that amanda knox did cartwheels in the waiting area. She says she was just stretching after a long wait. As far as cartwheels or splits, I never did a cartwheel. I did do the splits. And then later on she claimed that I was doing a whole number of gymnastics -- cartwheels, back walk-overs. I did the splits. And that's once. Reporter: But do you see how strange -- well, what's strange is why they things got mischaracterized. Reporter: But again, you can see that this does not look like grief? Does not read as grief. I think everyone's reaction to something horrible is different. Reporter: And perhaps most startling, this video, the first time much of the world will see newscasts. She's outside the house where the body's been discovered. And people kept saying, where is the anguish? Where is what we think we would do if this happened to our friend? I've seen the same picture, like the kissing just can't stop. And that's not what that was. Reporter: Kissing over and over again on the news. But when you look at the tape, there's three, quick kisses. And then, the rest of the time, she stares into space. She says thinking about how random fate because she lived in that house, too. My friend had been murdered. And it could just have easily been me. Somehow she had died in the house where we were living. And it could have been me. Reporter: But watching her, police are sure they have killer. That american girl. When we come back -- did you kill meredith kercher? skin.
This transcript has been automatically generated and may not be 100% accurate.