Amanda Knox Calls Italian Supreme Court Ruling 'Incredibly Painful'

April 30, 2013 — -- Amanda Knox's freedom is once again on the line.

After the Supreme Court of Italy annulled her acquittal last month, Knox now waits to go back on trial.

In an exclusive interview with ABC News' Diane Sawyer, Knox said of the decision, "It was incredibly painful."

Knox spent four years in prison before an Italian appeals court threw out her murder conviction in 2011 and she had been hoping the Italian Supreme Court would uphold the appeals court ruling and end her six-year ordeal.

"I felt like after crawling through a field of barbed wire and finally reaching what I thought was the end, it just turned out that it was the horizon," Knox said. "And I had another field of barbed wire that I had ahead of me to crawl through."

Watch Amanda Knox in an exclusive interview with Diane Sawyer set to air Tuesday at 10 p.m. ET.

The marathon legal battle will continue for Knox and for her ex-boyfriend, Raffaele Sollecito, who had been convicted along with her.

The court also refused to vacate her conviction for slander over her identifying her employer, Patrick Lumumba, as the person who killed Kercher. It was a statement, she claimed, she made under police duress.

Knox already served the three-year prison sentence for the slander conviction.

Knox's lawyer, Carlo Dalla Vedova, told ABC News he expects a new trial to begin in the next year. The trial is at the appellate level and will take place in Florence, Italy.

FULL COVERAGE: The Amanda Knox Case

Right after the ruling came down, Knox told ABC News, "I was so convinced that it was finally going to be over, but it just means that it's all the more important that I say what happened and keep fighting for what's right."

Knox does not have to return to Italy for the trial, and extradition is not currently on the table.

If she is convicted again, that ruling would be appealed up to the Italian Supreme Court.

Only if the supreme court upheld a guilty verdict could extradition even begin.

More legal proceedings would be necessary to extradite Knox to Italy. Many experts ABC News contacted did not believe such an effort would be successful.

"There is a treaty about cooperation on extradition between America and Italy with the possibility to extradite a citizen," said Dalla Vedoca, Knox's lawyer. "But an American citizen would be subject to authorization from the [United States] government."

Knox said she is ready to fight again.

"If there needs to be a re-evaluation of looking into the facts, that's fine," she said. "Because facts are facts and I'm not afraid of them."

Knox's memoir, "Waiting to Be Heard," is being released on today. The book reveals details about Knox's ordeal and a letter she had written to the victim's family, but she said her lawyers asked her not to mail it.

"It's not fair that there is not a satisfactory answer for what happened to Meredith, and the attention that's been taken away from her and what happened to her is not fair," Knox said.

Kercher's family, which had been clearly disappointed when Knox and Sollecito were freed, said it was "happy" with the Italian Supreme Court's ruling, the Italian news agency ANSA reported.

The court's judges have 90 days to write their "motivation," explaining in detail why they overturned the acquittal.

[Image credit: Ida Astute/ABC News]