Amanda Knox flew back to the United States yesterday after four years in an Italian prison for murder, while the victim’s father slammed her acquittal as “ludicrous” and “crazy”.

Ms Knox flew from Rome to London with her family and then boarded a connecting flight to her hometown of Seattle, the scene of jubilation among her supporters as they watched on television the verdict read out in an emotion-filled Italian courtroom on Monday.

The exhausted but smiling 24-year-old, wearing a grey cardigan and carrying a black shoulder bag, could be seen in the VIP lounge of Rome airport before leaving Italy, where she had come as a year-abroad student in 2007.

Mr Knox had been convicted along with two others and sentenced to 26 years in prison for taking part in the murder and sexual assault of her British housemate Meredith Kercher, then 21, who was found stabbed to death in the cottage they shared.

“This result is crazy. It makes a mockery of the original trial,” Ms Kercher’s father John was quoted as saying by the British tabloid Daily Mirror.

“There were 47 knife wounds on Meredith and two knives used. One person couldn’t possibly have done that,” said Mr Kercher, who did not attend the verdict.

Ms Knox’s ex-boyfriend Raffaele Sollecito, who also had appealed his conviction on the same charges, was likewise acquitted on Monday in the university town of Perugia in central Italy where Ms Knox and Ms Kercher were studying.

The only person now convicted of the crime is local drifter Rudy Guede, who is serving 16 years after his earlier appeals were rejected.

Mr Guede has said he was in the house at the time of the murder but did not kill Ms Kercher and said that he regretted not being able to save her life.

Ms Kercher’s mother, brother and sister, who travelled to Italy to hear the verdict, said the truth of what really happened on the night their loved one was killed on November 1, 2007, had suddenly been thrown into doubt.