Amanda Knox's lawyer argued Tuesday there wasn't sufficient evidence to convict the U.S. exchange student in the 2007 slaying of her British roommate, saying Knox had been swept up by a "tsunami" of events that led to her arrest.

In his closing arguments in the year-old trial, defense lawyer Carlo Dalla Vedova told jury members it was their duty to clear the American of all charges because the prosecution's case was flawed.

"If there is any doubt, if the evidence is not serious, reliable and coherent, I urge you to clear this girl," he said.

In nearly six hours of remarks, Dalla Vedova charged that key DNA evidence in the case cannot be attributed "beyond any doubt."

"There are still many doubts in this trial, and there's a young girl waiting to be judged," he told the eight-member jury, which is expected to issue a verdict Friday or Saturday.

The Seattle-born Knox and her former Italian boyfriend Raffaele Sollecito are being tried in Perugia, central Italy, for the slaying of Meredith Kercher. Both deny wrongdoing.

Kercher's body, her throat slit, was found in a pool of blood on Nov. 2, 2007, in the apartment she shared with Knox in Perugia. Prosecutors argued that Knox resented her British roommate and killed her, together with Sollecito and Rudy Hermann Guede of Ivory Coast, under "the fumes of drugs and possibly alcohol."

Prosecutors say a knife with a 6 1/2-inch (16.5-centimeter) blade, with Kercher's DNA on the blade and Knox's on the handle, was found at Sollecito's house.

Defense lawyers have argued that the knife is too big to match Kercher's wounds and claim the amount of what prosecutors say is Kercher's DNA is too low to be attributed with certainty.

Dalla Vedova also countered prosecutors' claim of a possible motive for the slaying. Prosecutors have charged Knox wanted to get back at Kercher for saying she wasn't clean and was promiscuous.

"We need facts, not only vague statements," said Dalla Vedova, who contended that any such resentment couldn't explain the violent killing.

He also contended that it had not been proved in court that Knox, Sollecito and Guede had plotted an attack on Kercher. "It needs to be proven that the three knew each other, had made arrangements, telephone calls, contacts," he said. "There must have been some sort of preparation. You don't carry out such a gruesome killing with people you don't know."

Prosecutors contend that Knox, Sollecito and Guede met at the apartment before the killing, possibly to settle some drug issues with the Ivorian.