"The motive is fundamental," attorney Carlo Dalla Vedova told the jury in Perugia, Italy, where Knox has been jailed for the last two years. "But today the motive has been changed at the last minute."
During a preliminary hearing, prosecutors claimed that Knox and two men slit Kercher's throat during a sex game gone awry. Prosecutors said during their summations last week, however, that Knox wanted revenge on her "prissy" roommate for criticism over being sloppy and bringing boys back to their apartment late at night.
Prosecutors have asked that Knox be sentenced to life in prison and be ordered to pay $12 million in damages to Kercher's family.
"At the very end of the trial the prosecution has changed the motive, not in the course of the trial and supporting it with evidence," Dalla Vedova said. "It is no longer the result of a sex party gone wrong. Now it is Amanda who organized the crime out of vengeance."
He noted that seven of Kercher's friends testified that Kercher had criticized Knox for her cleaning habits, for her guitar playing, because she brought boys home - the usual problems that come up when girls live together.
"And yet it is from this hate that everything else is meant to follow - according to the prosecutor, it is all Amanda, Amanda against another girl," Dalla Vedova said.
"You have to explain the hate to me. Where is it?" the lawyer asked. "This cannot be used as evidence."
Dalla Vedova, speaking on the second day of summations for the defense, said in the days after Kercher's body was found on Nov. 2, 2007 in the cottage they shared, Knox didn't flee, despite offers of a haven from the violence by family members at home in Seattle or in Germany.
"Amanda stayed in Perugia, she did not run away. She did not go to Germany when her aunt told her to come. On the morning of the 5th, the day she was interrogated, she went to school. She wanted to be in Perugia," Dalla Vedova told the jury.
Knox, he said, was a "clean-faced young girl. I know her well. And she was swept away by a tsunami" of events.
He described the police investigation as an "incredible evolution of facts that led to the arrest of Amanda Knox. It was a sort of rush."
The lawyer said police looked at Knox as a suspect because she behaved oddly in the days after the murder, including doing a cartwheel in a police station while waiting to be questioned, behavior he explained by saying she as "a girl who was alone on the other side of the world from her family."
"She became a suspect based on her behavior... They called her an assassin based on the fact she did a cartwheel," Dalla Vedova said.
"It was a mistake from the beginning. Police focused on Amanda and they were wrong," he said.
He disputed the impression that Knox was cold and uncaring while at the police station in the days after the Kercher's murder. He quoted the testimony of a court interpreter who said that on Nov. 4 she saw Knox in a waiting room at the police station. The witness, said Dalla Vedova, said Knox was pale, and looked ill and the interpreter was worried about Knox who said that she had not eaten or drunk anything all day.