Amanda Knox heads back to the United States

Amanda Knox cries after hearing the verdict overturning her conviction in the murder of Meredith Kercher, at the Perugia court, Italy, Oct. 3, 2011.

(CBS/AP) PERUGIA, Italy - Newly freed Amanda Knox headed home to the United States on Tuesday. Her departure from Italy comes a day after an Italian appeals court overturned her conviction of sexually assaulting and killing her British roommate Meredith Kercher.

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Knox, 24, arrived at the Rome airport in a Mercedes with darkened windows and waited for boarding inside a private waiting area Tuesday, out of public view and away from the media. She was headed to London, where she will catch a connection flight to the United States.

Knox and her then Italian boyfriend, Raffaele Sollecito, were convicted of sexually assaulting and murdering 21-year-old Kercher, who shared an apartment with Knox in Perugia. Knox was convicted to 26 years, Sollecito to 25. Both had been in prison since Nov. 6, 2007, four days after Kercher's body had been found at the apartment.

The family of Kercher appeared overwhelmed at the ruling, saying they were shocked and bewildered by the stunning reversal of the 2009 decision. The prosecutor said he would appeal the decision releasing Knox and Sollecito.

"It was a bit of a shock," said Stephanie Kercher, the victim's older sister. "It's very upsetting ... We still have no answers."

Meanwhile Lyle Kercher, the victim's brother, said the family has been left to wonder who is guilty. A third man has been convicted in the brutal slaying, however his trial concluded he did not act alone.

"If the two released yesterday were not the guilty parties, we are obviously left to wonder who is the other guilty person or people. We are left back at square one," Lyle Kercher said.

Prosecutor Giuliano Mignini expressed disbelief in the verdict and vowed an appeal to Italy's highest criminal court.

If the highest court overturns the acquittal, prosecutors would be free to request Knox's extradition to Italy to finish whatever remained of a sentence. It is up to the government to decided whether they make such a request.

The jury upheld Knox's conviction on a charge of slander for accusing bar owner Diya "Patrick" Lumumba of carrying out the killing. The judge set the sentence at three years which is less than the time Knox had spent in prison.

Knox dissolved into tears as the verdict was read after 11 hours of deliberations and she needed to be propped up by her lawyers on either side. Two hours later, she was in a dark limousine that took her out of the Capanne prison just outside Perugia, where she had spent the past four years and headed to Rome.

Complete coverage of Amanda Knox on Crimesider