On Saturday for the first time, the court heard testimony in defense of Knox's former boyfriend Raffaele Sollecito.
Kercher was found dead in her bedroom in the apartment she shared with Knox on Nov. 2, 2007.
Prosecutors say that Knox, Sollecito and a third man, Rudy Guede, killed Kercher in a sex game gone wrong. Guede has been convicted of sexual assault and murder and sentenced to 30 years in prison.
On Saturday, lawyers for Sollecito called longtime acquaintances to testify on Sollecito's behalf.
They described him as a calm young man who rarely used drugs.
"The television described him as a womanizer, in fact he was shy and introverted," said Saverio Pinetti Mofetta, who has known Sollecito for 10 years.
Inexperienced Sollecito Excited About New Relationship With Knox
Mofetta said Sollecito called him on the night of the murder. "He was worried because it happened at his girl's place and it could happen again," he said.
In the days that followed the murder, Knox was photographed in an intimate embrace with Sollecito. The image fueled the prosecution's characterization of Knox as a promiscuous, drug-abusing young woman who, together with Sollecito and Guede, forced Kercher to take part in an orgy against her will.
Sollecito's college friend, Angelo Cirillo, said Sollecito was sexually inexperienced but excited about his new relationship with Knox. Prosecutors asked him to explain a photograph in which Sollecito is shown wielding a meat cleaver. Cirillo described it as a college prank.
"I took that picture and did him up that way," he said. "I wrapped him in toilet paper."
Knox has testified that on the night of the murder she and Sollecito smoked marijuana and had sex at his apartment before she returned to her apartment and discovered Kercher's body.
During the trial, Knox and Sollecito have often appeared in the courtroom at the same time and have exchanged letters. On Friday he gave her a chocolate, apparently for the second time.
Sollecito Always Carried His Knife: 'He Used It to Cut Fruit or Pizza'
"Raf is a big romantic," said Mariano De Martino, who has known Sollecito since the age of 7. De Martino said that Sollecito would occasionally smoke hashish, but that "he never actively looked for drugs."
In their testimony, Mofetta and De Martino said Sollecito never became violent while under the influence.
Both men were asked about a small knife Sollecito was known to carry. Kercher was found with her throat slashed. Prosecutors have suggested that a kitchen knife found in Sollecito's apartment is the murder weapon, but the knife Sollecito carried was described as much smaller.
"Raffaele wore his knife as a garment," said De Martino. "He always carried it in his pocket or hanging from his trousers by a hook, but he never showed it off."
Mofetta agreed. "He used it to cut fruit or pizza. He didn't want anybody to touch it, he was afraid we'd get hurt."
Prosecutors contend that Knox and Sollecito stole Kercher's credit cards and cash, and staged a break-in to paint the murder as a botched robbery attempt. Guede has a record of petty crime, including theft. Victims of his crimes say Guede threatened them with a knife.
Both Knox and Sollecito, who face life sentences if convicted, say they are innocent. A verdict is expected in the fall.
Knox's mother and younger sisters were in Perugia to support their sister.
"Amanda is innocent and when the trial is over, she will certainly come back home," said Knox's younger sister, Deanna, 20.
With reporting from Perugia, Italy, by Enzo Berett and Malaika Bova in London.