An Italian court cleared 24-year-old American Amanda Knox and her former boyfriend of the 2007 killing of British student Meredith Kercher and ordered they be freed on Monday after nearly four years in prison for a crime they always denied committing.

Seattle native Knox and Italian computer student Raffaele Sollecito, had appealed against a 2009 verdict that found them guilty of murdering 21-year-old Kercher during what prosecutors had said was a drug-fueled sexual assault four years ago.

A whoop of joy was heard in the court as the ruling overturning their sentences was read out but Knox herself broke down and was led out sobbing and supported by police officers.

As you could see from the images, Amanda was a nervous wreck who just collapsed. She wasn't able to say anything other than 'thank you' in a flood of tears, one of her lawyers Maria Del Grosso told reporters.

Knox was expected to return to the Perugia jail where she has been held to complete formalities before walking free but her lawyers said they did not know where she would be spending her first night of freedom.

The verdict, a severe embarrassment to the Italian justice system, came after independent forensic investigators sharply criticized police scientific evidence in the original investigation, saying it was unreliable.

Kercher's half-naked body, with more than 40 wounds and a deep gash in the throat, was found in 2007 in the apartment she shared with Knox in the Umbrian hill town of Perugia where both were studying.

Both Knox and Sollecito, 27, had consistently maintained their innocence throughout the original investigation and trial. A third man, Ivorian drug dealer Rudy Guede, was imprisoned for 16 years for his role in the murder.

Sollecito's father, a doctor, said the court had given me back my son.

It was obvious that he had nothing to do with the death of that poor girl, he said. I finally allowed myself to cry.

The court upheld a conviction against Knox for slander, after she had falsely accused barman Patrick Lumumba of the murders. It sentenced her to three years in prison, a sentence which she has now already served.

STUNNED

Kercher's family members sat stunned in the court long after the others had left. Meredith's sister Stephanie was in tears.

We respect the decision of the judges but we do not understand how the decision from the first trial could be so radically overturned, the Kerchers said in a statement released through the British embassy.

We still trust the Italian judicial system and hope that the truth will eventually emerge.

But on Knox's side, there was unrestrained delight.

She's a girl who wants to live, she wants to go home, she wants to go to Seattle, she wants to be with her family and so I think she will spend some time to get over these four years in prison, one of her legal team, Carlo Dalla Vedova said.

The appeal trial gripped attention on both sides of the Atlantic, with an outpouring of sympathy and outrage from many in the United States who saw the American as an innocent girl trapped abroad in the clutches of a medieval justice system.

State Department spokeswoman Victoria Nuland said the U.S. embassy in Rome would continue to assist the Knox family, adding: The United States appreciates the careful consideration of this matter within the Italian judicial system.

A powerful lobbying campaign by her family played a big part in changing perceptions of Knox from the promiscuous Foxy Knoxy of early media reports and the cold-blooded, sex-obsessed she-devil portrayed by prosecutors.

But the verdict was not universally welcomed. Outside the court hundreds of people whistled, booed and shouted Shame, shame and bastards at the courtroom and U.S. TV crews.

During the appeals trial Knox's plight in jail dominated much of the reporting, leaving Kercher's family feeling that the real victim of the crime had been pushed to one side.

Mez has been almost forgotten in all of this, her sister Stephanie told a news conference before the verdict, as the family emphasized that the brutality of the crime must not be forgotten.

Kercher, a Leeds University student from Coulsdon in Surrey, was on a year-long exchange program in Perugia when she was murdered, bringing a flood of unwelcome attention to the medieval town in central Italy that her family said she loved.

The murder investigation showed she was pinned down and stabbed to death. Prosecutors said that she resisted attempts by Knox, Sollecito and Guede to involve her in an orgy.

But their case was weakened by forensic experts who dismissed police evidence that traces of DNA belonging to Knox and Kercher were found on a kitchen knife identified as the murder weapon.

The experts also said alleged traces of Sollecito's DNA on the Briton's bra clasp may have been contaminated.

The defense argued that no clear motive or evidence linking the defendants to the crime had emerged, and said Knox was falsely implicated in the murder by prosecutors determined to convict her regardless of the evidence.

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