Amanda Knox reacting to an interviewers questions about a Florence court upholding the guilty verdict for her and her former boyfriend during her recent interview on ABC's Good Morning America show in New York

Knox was sentenced to 28 years in prison by a court in Florence for murder. She already served four years for the crime, returning to Seattle in 2011. The U.S. Supreme Court has to confirm the guilty verdict before extradition. Critics say no Secretary of State will ever send her back to Italy.

Attempts by Rome to extradite Amanda Knox from the United States are doomed to failure, diplomatic sources have warned.

The 26-year-old American is at the centre of a diplomatic tug of war after an Italian court on Thursday sentenced her to 28 years prison for the murder of British student Meredith Kercher.

Knox served four years jail for the 2007 murder, but returned home to Seattle in 2011, when she and former boyfriend Raffaele Sollecito were acquitted on appeal.

Following the dramatic quashing of that acquittal, followed by the reinstatement of her conviction, Knox said she will never willingly go back to Italy, and will instead become 'a fugitive'.

Once the murder sentence is confirmed by the Supreme Court, Italy can apply for Knox's extradition and arrest.

But despite expected Italian efforts, experts say the US State Department will never send Knox back to a country where she was allegedly beaten by police and interrogated for hours without a lawyer or translator.

Thanks to a powerful public relations campaign, and a prison memoir, Knox has successfully won over millions in the US to her cause counting Donald Trump among her supporters. Even early on senators petitioned Hilary Clinton on her behalf, claiming it was 'an anti-American trial'.

And US State Department sources now reveal the 26-year-old has little to fear as she will be protected by the strength of public opinion in America.

The Rome-based source confided: 'We will never send her back to Italy. It's obvious she hasn't had a fair trial.'

Once the guilty verdict is confirmed by the Supreme Court, Italy will almost certainly apply to extradite Knox, because of the expectation from the public to do so, another foreign policy expert said.

'They will have go through the motions because of the public pressure to do so, even though they know it will fail. No American Secretary of State will ever send her back, the source claimed.

He added: 'The Italians have to support own judiciary. They can't just do nothing when the judiciary sentence someone for murder.'

In the same way, Britain used to routinely apply for the extradition of criminals living on the Costa del Sol, knowing that the attempts were wasted efforts, he explained. 'But the government can't be seen to do nothing'.