Prosecutors have appealed the acquittal of U.S. student Amanda Knox, who was on trial in Italy for the murder of her British roommate, Meredith Kercher, in the university town of Perugia about four years ago.

Perugia prosecutors filed an appeal in Italy's highest court on Tuesday, more than four months after a court threw out the charges against Knox, reported CBS. Prosecutor Giovanni Galati said he was very convinced that Knox, along with her boyfriend at the time Raffele Sollecito, was responsible for the death of the 21-year-old British national.

Knox's family was not surprised that the prosecution has appealed the case.

We are not concerned about this appeal as Amanda's innocence was clearly and convincingly proven in her appeal trial, the family said statement, according to ABC. This is simply another example of harassment by the prosecution against Amanda and makes this terrible, painful incident continue to go on for Amanda, Raffaele and their families.

If the appeal is granted, Knox could be retried and extradited back to Italy. However, her lawyers were confident that would not happen.

We're not considering that possibility; for us she has been acquitted, said one of her lawyers, Luciano Ghirga, according to the New York Times. That's how the system works, but for us it's a hypothesis far into the future.

Carlo Dalla Vedova, another lawyer representing Knox, criticized the prosecution for appealing the case, saying it would reopen painful wounds.

I am sorry for the two kids, he said of. Knox, 24, who moved back to her hometown, and Sollecito,  who has been living in southern Italy.

The Italian high court cannot hear new evidence and will base their decision on what was submitted at earlier trials.

In their original case against Knox and Sollecito, the Italian prosecutors suggested that they killed Kercher in a drug-fueled rampage and a bizarre sex game, along with a third man, Rudy Guede, reported the New York Times. The body of Kercher was found in the house she shared with Knox with a slit throat.

Guede was found guilty of participating in the murder of Kercher and is serving 16 years in prison.

However, prosecutors presentenced questionable DNA in their cases against Knox and Sollecito. After an independent review, the DNA was discovered to not be reliable and the courts ruled that the prosecution no longer had a viable case.

Dalla Vedova said that her client is not concerned about any appeal made by the Italian government because her innocence was already proven.

We're just sorry she has to deal with all this again.