American student Amanda Knox arrived home in Seattle on Tuesday after an Italian appeals court overturned her murder conviction—a ruling that is fueling questions about the credibility of the Italian justice system.

Amanda Knox, center, is comforted by her sister Deanna, right, and mother, Edda Mellas, at a news conference after her arrival in Seattle Tuesday. Getty Images

Ms. Knox landed in Seattle shortly after 5 p.m. on a direct flight from London's Heathrow Airport.

"Thank you to everyone who believed in me, who has defended me, who has supported my family," Ms. Knox said in a brief, tearful statement. "Family's the most important thing to me right now, and I just want to be with them."

After spending four years in prison, Ms. Knox's first taste of freedom came Monday in the form of a hectic travel schedule aimed at returning her to Seattle as quickly as possible. She traveled by carto Rome, where she boarded a U.S.-bound flight with a layover in London.

By the time she arrived in Seattle a crowd of supporters had swelled at a makeshift conference area near where shuttle buses collect travelers leaving SEA-TAC airport with their luggage. One person, a Jordanian-American named Joseph Zumot, came with leaflets protesting the what he said was the wrongful conviction of his brother, Bulos, for murder of his girlfriend. It's a case, Mr. Zumot said, "just like Amanda's" as he passed out information on the case and chatted with visiting reporters.

In the wake of her departure, Italy was left to soul-searching over how the Perugia court—and the Italian justice system in general—could swing so dramatically in its assessment of Ms. Knox.

Amanda Knox smiles as she goes through Italy's Leonardo da Vinci-Fiumicino Airport on Tuesday before boarding a flight back to the U.S. Reuters

In her first trial, Ms. Knox was depicted as a demonic figure and she and her then-boyfriend Raffaele Sollecito were convicted two years ago of murdering U.K. national Meredith Kercher in a 2007 sexual assault. The appeals court repudiated that ruling on Monday, overturning the murder conviction and setting Ms. Knox free from a 26-year prison sentence.

News of the verdict drew hundreds of Perugians to the courthouse to protest the ruling, shouting: "Shame on you!" On Tuesday, the verdict was splashed across the front pages of Italian newspapers that questioned whether the appeals ruling had been unduly influenced by a perceived media campaign to free Ms. Knox.

Other headlines raised questions about whether Italian trials should continue to heavily rely on circumstantial evidence, like that used to convict Ms. Knox in the first trial, when there is a lack of physical evidence and clear motive.

"Last night's verdict will certainly give traction to new bitter polemics over the workings of justice in our country," wrote Fiorenza Sarzanini in a front-page editorial in Corriere della Sera, Italy's biggest daily.

An Italian appeals court on Monday acquitted American student Amanda Knox of murdering her roommate, a stunning turnaround. Stacy Meichtry has details from Perugia, Italy on The News Hub.

"The question that rightly comes to mind is: Who is going to pay back Amanda Knox if her imprisonment was unjust?" said Angelino Alfano, secretary of Prime Minister Silvio Berlusconi's conservative party and a former justice minister.

A major turning point in the appeals trial was the court's decision to allow an independent panel of forensics experts to review DNA evidence that had been used by prosecutors to convict Ms. Knox and Mr. Sollecito in the first trial. Prosecutors said the traces of DNA found on the handle of a knife, the alleged murder weapon, matched that of Ms. Knox. But the panel of experts delivered a report to the appeals court that said the amounts of DNA found on a knife were too small to make a conclusive match to anyone.

Lyle Kercher, brother of the late Ms. Kercher, said his family was struggling to comprehend how the appeals court could overturn a decision that was "so certain two years ago."

Mr. Kercher also hinted at contradictions that arose from the Italian justice system's approach to prosecuting Ms. Knox and Mr. Sollecito in one trial while granting a separate fast-track trial to Rudy Guede, an Ivory Coast national. Mr. Guede has been convicted of murdering Ms. Kercher and sentenced to 16 years in prison, having exhausted the appeals process. In the trial of Mr. Guede, who continues to deny having a role in the murder, the court ruled that he didn't act alone, but the court didn't name Ms. Knox and Mr. Sollecito.

"If the two released [Monday] 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," Mr. Kercher told reporters during a news conference at his hotel in Perugia on Tuesday.

Italian prosecutors have criticized Monday's ruling, vowing to appeal it to Italy's highest court in the coming weeks.

If the high court were to order another trial and Ms. Knox were to be convicted in that new proceeding, then Italy could seek her extradition from the U.S., but these scenarios are considered extremely unlikely.

Write to Stacy Meichtry at