Amanda Knox will be retried for the murder of Meredith Kercher. REUTERS

Amanda Knox was acquitted of murder in October, but Italian prosecutors are challenging the judges' ruling. Prosecutors in the city of Perugia, where the Seattle-born student was found guilty of killing her roommate Meredith Kercher in 2007, have filed for an appeal with Italy's Supreme Court.

The criminal court will decide if it wants to take on the case by the end of the year. During Knox's first appeal last year, it seemed like the court was equally likely to rule either way. As with most things in Italy, the course of events were entirely unpredictable.

However, prosecutors will have a harder time reinstating the guilty verdict in the re-trial. The court is not allowed to hear any new evidence, and so must rely on evidence that has already been called into question during previous hearings.

Moreover, Knox will not have to testify or even appear in court.

Knox and her then-boyfriend Raffaele Sollecito were convicted of Kercher's murder in 2009 and sentenced to 26 and 25 years in prison respectively. In October, at the conclusion of a 10-month long appeals trial -- the first of two allowed under Italian law -- both were acquitted of the crime and freed.

During the appeal, court-appointed experts called into question the key evidence used against Knox in the first trial -- notably the DNA found at the crime scene and the murder weapon. The experts said in June that the DNA could have been tainted during the initial police investigation, which was itself full of inconsistencies and breaches of protocol.

The most damning DNA evidence was a bra-clasp found six weeks after Kercher's murder, but the traces were too small to be retested by the court.

The murder weapon has also been called into question and the knife found in Sollecito's apartment, which had Knox's DNA on it, did not match two of three wounds found on Kercher's body.

Additionally, the only person who testified that he saw Knox and Sollecito at the apartment on the night of the murder turned out to be a heroin addict who confused many details of the incident when questioned.

After the appeals trial, Judge Claudio Pratillo Hellmann blasted the original police investigation and said that the argument for Knox's guilty verdict, which included sex-games and satanic rituals, was not based in fact.

Even taken all together, [the evidence doesn't] prove in any way the guilt of Amanda Knox and Raffaele Sollecito for the crime of stabbing Kercher in the Perguia flat they shared, the judge wrote.

[The verdict] was not corroborated by any objective element of evidence and in itself was not, in fact, probable: the sudden choice of two young people, good and open to other people, to do evil for evil's sake, just like that, without another reason.

Aside from a momentary and poorly translated confession made when she was first interrogated by police, Knox maintained her innocence throughout the ordeal.

I didn't rape. I didn't steal. I was not there, she said in Italian during her final address to the Perugia court.

We had a good relationship. We were all available to each other. I shared my life, especially with Meredith. We had a friendship. We were friends. She was concerned for me. She was always kind to me. She cared about me.

On Tuesday, Knox's family responded to the Supreme Court appeal, calling it simply another example of harassment by the prosecution against Amanda.

Despite Knox's acquittal and years of trials, the events of the night of Kercher's murder are still unknown.