Knox, an American from Seattle, was jailed for 26 years
Judges in Italy have published their reasons for convicting Amanda Knox and her ex-boyfriend Raffaele Sollecito for the murder of Meredith Kercher.
The judges said the murder happened without planning or grudge.
They said there were no holes or inconsistency in the evidence and that the evidence suggested there was a sexual motive in the case.
The pair were found guilty in December of killing Ms Kercher, from Coulsdon, Surrey, in Perugia in 2007.
Both Knox and Sollecito are appealing against their convictions; Knox on the grounds that the forensic evidence against her was flawed.
In the 427-page opinion document, Italian judges Giancarlo Massei and Beatrice Cristini say all their decisions were based on the forensic evidence presented.
Miss Kercher had been studying Italian on an exchange programme
They say, for example, that one footprint found in Miss Kercher's bathroom belonged to Sollecito, whilst another in a bedroom came from Knox.
And they explain, at length, why the footprint in the bedroom is a woman's.
BBC Rome correspondent Duncan Kennedy said this suggested they had dismissed some of the more lurid claims of the prosecution, especially concerning Knox, over things like her cart-wheeling and giggling in the police station in the days after the murder.
In their explanation, the judges also say that Knox and Sollecito had staged a fake break-in to make it look as though Miss Kercher was killed by an intruder.
In part of the report, the judges suggest a sexual motive lay behind the killing.
They say that Knox and Sollecito went to Meredith Kercher's house with a third man, Rudy Guede, a small-time drug dealer, who was convicted of murder at a separate trial.
The report says that, under the influence of drugs, Knox and Sollecito "actively participated" in helping Guede subdue Miss Kercher so that Guede could "give vent to his lustful impulses" in what they called his "evil act".
The motive, the judges say, was "erotic sexual violence", where Knox and Sollecito had probably found holding Miss Kercher down was "exciting".
But, in their interpretation of events, the judges say this was a murder "without planning, without any animosity or grudge against the victim".
They say the death was the result of what they call, "purely random circumstances" that Knox and Sollecito had not gone specifically to kill Miss Kercher.
This view is reinforced by another extract from the judges' report.
It says the fact that Miss Kercher's body had been covered by her attackers showed, "a sort of regret for what they had done".
Knox was jailed for 26 years and Sollecito for 25 years in December last year.
Guede, 22, was sentenced to 30 years for his part in the murder in 2008.
The judges also noted that early on in the investigation, Knox had "freely accused" another man, Patrick Lumumba, knowing he was innocent.
Miss Kercher, 21, a Leeds University student, had been sharing a house with Knox, who was also a student, on a year abroad in the Umbrian hilltop town.