Another Kercher family lawyer, Vieri Fabiani, said the verdict showed that criticisms of the Italian justice system had been unfounded. “In the end,” he said, the verdict showed that the system “protects the rights of defendants more than other systems.”

Neither Ms. Knox nor Mr. Sollecito was present in the courtroom on Friday. Ms. Knox has been living in the Seattle area since her original conviction was overturned in October 2011, and had said she would not willingly return to Italy if the court’s decision had gone against her. Mr. Sollecito attended the case’s two days of hearings before the court, but chose to await the verdict elsewhere.

Ms. Knox and her family issued statements through her defense team expressing deep thanks for the court’s ruling.

“I am tremendously relieved and grateful for the decision of the Supreme Court of Italy,” Ms. Knox said. “The knowledge of my innocence has given me strength in the darkest times of this ordeal. And throughout this ordeal, I have received invaluable support from family, friends, and strangers. To them, I say: Thank you from the bottom of my heart. Your kindness has sustained me. I only wish that I could thank each and every one of you in person.”

Ms. Kercher was found dead on the morning of Nov. 2, 2007, lying on the floor of her bedroom in Perugia, a university town in central Italy that is popular with foreigners.

Ms. Knox and Mr. Sollecito were arrested a few days later, and spent four years in custody before their original convictions were overturned.

Rudy Guede, a Perugia resident born in the Ivory Coast, was convicted of murder in a separate trial in connection with Ms. Kercher’s death, as one of three assailants. Defense lawyers for Ms. Knox and Mr. Sollecito had always argued that Mr. Guede committed the crime on his own.