Investigative journalist Graham Johnson, co-author of Darkness Descending: The Murder of Meredith Kercher, outlines 10 factors that helped Amanda Knox and Raffaele Sollecito win their appeal.
1. Reasonable doubt
Amanda Knox's lawyers managed to instil reasonable doubt in the jurors' minds over the quality of testing of the bra clasp belonging to Meredith Kercher - which it was claimed had Raffaele Sollecito's DNA on it - and the knife that prosecutors argued was the murder weapon. The prosecution maintained Knox's DNA was on the handle of the kitchen knife, with Ms Kercher's DNA on the blade. The defence claimed that the amount of Meredith Kercher's DNA on the blade was too small to test. An independent review disputed the prosecution's claims.
2. Crime scene errors
A few police crime scene errors, such as contaminated samples, lost evidence and disputed procedures, were successfully portrayed as generalised incompetence. An independent review raised doubt over the attribution of some of the DNA traces, which were collected from the crime scene 46 days after the murder.
3. Lack of proof
There was no convincing proof that Amanda Knox and Raffaele Sollecito were actually in the room when Meredith Kercher died. Even the presence of Amanda Knox's blood and footprints in the house were successfully explained away. Her defence claimed that Knox's blood could have been there because she was a resident at the farm house on Pergola Road. The evidence of Rudy Guede against Knox was also confusing. Guede, who is serving a prison sentence for sexual assault and murder, said that he heard her voice at the scene but didn't see her face.
There was no credible motive for the murder. The prosecution stuck doggedly to the sex-game-gone-wrong explanation even though their own medical examiner said there was no evidence of rape in the days following the murder. An alternative motive, involving robbery, gained traction as the case rolled on, based on the unexplained disappearance of Meredith Kercher's 200 euro rent money.
5. Unreliable witness
One of the key witnesses at the original trial, a homeless man called Antonio Curatolo, publicly admitted to being a heroin addict, undermining his observations that he saw Knox acting suspiciously by the scene of the crime on the night of the murder in November 2007.
Knox claimed that some of the evidence put forward against her - stories about her strange behaviour after she was arrested and the prosecution's focus on her sexuality - was no more than an attempt to demonise her to cover up for a weak case.
7. PR campaign
Knox's family hired a Seattle public relations specialist, David Marriot, who for months repeatedly plugged the line: "Amanda will get out, it's a done deal." This created a self-propagating media frenzy, which - in the end - helped convince a largely sceptical Italian media.
8. Supporters' presence
The massive presence of friends and family in Perugia in support fuelled the "Amanda is innocent" campaign. Italians have claimed that because Knox is American, the case has been handled differently, so as not to offend the US.
9. Appeals process
The Italian appeals process offers more guarantees to defendants than any other legal system in the world, whereby only the weakest evidence is treated, not the whole case. Knox's team only had to attack the DNA evidence against her to undermine the whole edifice of the original trial. Italy has one of lowest prison populations in the world because of its lenient appeals process.
10. Favourable political climate
Silvio Berlusconi's government vowed to tame his country's fiercely independent system of magistrates - one that had been bolstered to fight the mafia. The more the government shows the magistracy to be incompetent the better for Mr Berlusconi. The ministry of justice is poised to investigate what went wrong.