Reporters on board the British Airways flight hoping to talk to Knox, now a tabloid staple on two continents, were blocked on the stairs by a flight attendant who politely informed them that the family would speak publicly after the plane touched down at Seattle-Tacoma International Airport.
It was unclear whether Knox herself would speak at the airport. She is expected to arrive at Sea-Tac Airport at about 5:15 p.m. Tuesday.
Knox's life, spent in prison for the last four years, turned around dramatically Monday when an Italian appeals court threw out her murder conviction in the death of her British roommate. The decision, fueled by doubts over DNA evidence, stunned the victim's family and angered the prosecution, which insists that she was among three people who killed 21-year-old Meredith Kercher.
Knox left Perugia's Campanne prison Monday night amid cheers that a companion compared to those at a soccer stadium.
Hundreds of inmates - most of them in the men's wing - shouted "Amanda, ciao!" and "Freedom!" as she walked into the central courtyard, said Corrado Maria Daclon, head of the Italy-US Foundation, which championed Knox's cause.
"They were screaming like crazy," said Daclon, who accompanied Knox in her first hours of freedom. Dalcon said Knox jumped a little for joy and waved to the prisoners.
She was soon on her way home, protected by the darkened windows of a Mercedes that led her out of the Capanne prison in the middle of the night, and then Tuesday morning to Rome's Leonardo da Vinci airport.
"Those who wrote, those who defended me, those who were close, those who prayed for me," Knox wrote in a letter released just hours before leaving the country, "I love you."
Knox thanked those Italians "who shared my suffering and helped me survive with hope," in a letter to the Italy-US Foundation, which seeks to promote ties between the two countries.
"During the trip from Perugia to Rome, Amanda was serene," said Daclon, who was with Knox in the car.
Knox flew from Rome to London, where she took a direct flight to Seattle, flying business class with full-length seat and menu options including champagne, smoked salmon and prawn salad.
At least nine members of media organizations were on board, but a British Airways attendant on the flight blocked them from the plane's secluded upper deck "to preserve the privacy" of passengers. The attendant, quoting a Knox family member, said media were not allowed to contact Knox or her family on the flight but were welcome to attend a press conference later in Seattle.
To Knox, the verdict means freedom after four years behind bars and under the spotlight of an international press focused on her every word or gesture. The case has been a cause celebre in the U.S., and a staple of British tabloids, which took to calling her "Foxy Knoxy."
"FREE," said local newspaper La Nazione on its front page, dominated by a huge photo of a crying Knox, overwhelmed by emotions as the verdict was read out Monday night in a packed courtroom in Perugia.
Prosecutors announced they are appealing the innocent verdicts of Knox and her former boyfriend, Raffaele Sollecito, to Italy's highest court.
Kerchner's family said during an emotional news conference Monday that they were back to "square one."
"If those two are not the guilty parties, then who are the guilty people?" asked Lyle Kercher, a brother of the victim.
Prosecutor Giuliano Mignini expressed disbelief at the verdict and said he will appeal to Italy's highest criminal court after receiving the reasoning behind the acquittals, due within 90 days.
"Let's wait and we will see who was right. The first court or the appeal court," Mignini told The Associated Press on Tuesday. "This trial was done under unacceptable media pressure."
Prosecutors maintain that Knox, Sollecito and another man killed Kercher during a lurid, drug-fueled sex game. Knox was sentenced to 26 years in prison and Sollecito received 25, but the prosecution's case was blown apart by a DNA review ordered during the appeals trial that discredited crucial genetic evidence.
Prosecutors maintain that Knox's DNA was found on the handle of a kitchen knife believed to be the murder weapon, and that Kercher's DNA was found on the blade. They said Sollecito's DNA was on the clasp of Kercher's bra as part of a mix of evidence that also included the victim's genetic profile.
But an independent review - ordered at the request of the defense, which had always disputed those findings - found that police conducting the investigation had made glaring errors in evidence-collecting. The two experts said below-standard testing and possible contamination raised doubts over the attribution of DNA traces, both on the blade and on the bra clasp, which was collected from the crime scene 46 days after the murder.
The review was crucial throwing out the convictions because no motive has emerged and witness testimony was contradictory.
The highest court's remit is to rule on whether any procedures had been violated, and the hearing generally takes one day in Rome. Defendants are not required to attend.
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 decide whether to make the formal extradition request.
One conviction in the slaying still stands: that of Ivory Coast native Rudy Hermann Guede. His lawyer said Tuesday he will seek a retrial.
Guede was convicted in a separate fast-track procedure and saw his sentence cut to 16 years in his final appeal. He says he is innocent, though he admits being in the house the night of the murder.
Defense lawyers maintain that Guede was the sole killer, while prosecutors say that bruises and a lack of defensive wounds on Kercher's body prove that there was more than one aggressor holding her into submission. However, they could never quite explain how Knox and Sollecito, who had been dating for less than a week, would be be involved in an extreme sexual scenario with somebody only one of them barely knew.
The highest court, in upholding Guede's conviction, said he had not acted alone. However, the court's ruling does not name Knox and Sollecito as Guede's accomplices, saying it was not up to the court to determine that.
Kercher family was perplexed, saying, in Lyle Kercher's words, that the decision "obviously raises further questions" since Guede's conviction remains. "As far as I understand, the courts agree he wasn't acting alone."
Alessandra Rizzo reported from Perugia, Italy. Associated Press writer Nicole Winfield in Rome contributed to this report.