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.