Knox's appearances on the stand marked a dramatic twist in the long case, which began in January, more than a year after the murder.
For the first time in public, Knox spoke about her relationship with Kercher and about her behavior after the murder, which had been characterized as strange and showing no remorse. Previous testimony included an account of Knox turning cartwheels at the police station after the killing, and being amorous with Sollecito.
"In general, I'm someone who tends to act a little silly when I feel I'm in difficulty or not at ease," said Knox, speaking in Italian.
"I cried, but I was always hugged by Raffaele," she said of her reaction to the discovery of Kercher's body. "First, he gave me his jacket, then he was cuddling with me because I was shaking. I didn't know what to think. I was shocked."
Knox disputed earlier suggestions that she didn't get along with Kercher, saying their relationship was friendly and open.
"I confided in her. I would often ask for her advice," testified Knox, speaking in Italian. "When Meredith had a problem over my behavior, she would tell me. That was it. There was nothing she would keep hidden or that we couldn't find agreement on."
Knox, who has been held in an Italian prison for 18 months, told the court that she had last seen Kercher on the afternoon of the murder, in the home they shared. Halloween was the night before, and Kercher still had vampire makeup on her face, Knox testified.
"She left her room, said 'bye,' walked out the door," Knox said. "That was the last time I saw her."
Knox and Kercher, both exchange students, were sharing the flat in Perugia for the semester.
On Nov. 2, 2007, Kercher was found stabbed and strangled to death in her room in the house she shared with Knox and two other women.
Knox's explanation of where she was during the murder has changed at least twice over the course of the case. Originally, she said she was not in the house. Later, Knox told police that she was in the house when Kercher was murdered and heard the victim scream.
On the stand she explained that, under intense police interrogation, she had "imagined" hearing the scream.
Wearing white and sporting a ponytail, Knox explained to the jury in a confident voice why she signed a statement at a Perugia police station implicating herself, a statement she now says was false.
"They got tough with me, called me a liar and said I was trying to protect someone," Knox said in English with an Italian translator standing by her side. She spoke in a confident voice and used her hands freely to emphasize her points.
She later switched to Italian, expressing frustration with the translation.
"I wasn't trying to protect anyone, so I didn't know how to respond," Knox said. She added, "I couldn't understand why they were so sure I was the one who knew everything."
She said police posed the same questions over and over again, repeatedly asking her who she thought had killed her roommate and asking her to go over exactly what she did the night Kercher died.
At one point, Knox told the jury, police hit her on the head.
"I was hit in the back of the head by one of the police officers who said she was trying to make me -- help me remember the truth," Knox said.
The Perugia police have repeatedly denied any misconduct on the night of the interrogation or at any other point.
The prosecution maintains that the confused testimony Knox gave to the police is a sign of her culpability.
The Associated Press contributed to this story.