Italy's high court says the investigation into the 2007 murder of British student Meredith Kercher, of which American Amanda Knox was convicted but acquitted on appeal, had "major flaws".
In March, the court acquitted Knox and her Italian ex-lover Raffaele Sollecito of Kercher's murder, ending an eight-year legal saga that saw the two convicted, acquitted and convicted again before being finally cleared.
In its 52-page explanation of the ruling released on Monday, the court underlined the absence of a "body of evidence" allowing for a conviction "beyond a reasonable doubt", saying there was no "biological trace" linking the two to the grisly murder.
Kercher, 21, died after being stabbed 47 times on November 2, 2007.
She was found half-naked, her throat slit, inside her locked bedroom in the flat she shared with Knox and two other Italian women in the central Italian university town of Perugia.
The court document said the fluctuations in the trial were the result of "major flaws" or oversights in the investigation as well as "omissions" in the police searches.
Judges said criminal investigations followed "an objectively inconsistent path" and were marred "by sensational mistakes or investigative black outs, and guilty oversights" in chasing up possible leads.
The court suggested that media frenzy over the affair distracted investigators, leading the prosecution into a "fitful search" for culprits "to be delivered to international public opinion".
The lack of reliable forensic evidence linking Knox and Sollecito to the murder scene, and the erasure of hard drive memory on computers belonging to Knox and Kercher were cited as key examples of how officers bungled the investigation.
Ivory Coast-born drifter Rudy Guede was jailed for the murder in 2008 but, in a judgment that was to have serious implications for Knox and Sollecito, the judge in his trial ruled that he could not have acted alone.
Prosecutors maintained to the end that Knox and Sollecito fatally slashed Kercher while Guede held her down.
Knox and Sollecito were first convicted in 2009, then acquitted in 2011, when they believed they had been freed to resume normal lives.
But that decision was found to be flawed by the Court of Cassation in 2013, leading to a retrial in Florence which reinstated the initial convictions and increased Knox's sentence to 28 years and six months.
Then in a dramatic finale in March, Italy's top court threw out Knox's conviction, after 10 hours of deliberation.
Since her release, Knox had completed the language studies that took her to Perugia in the first place, found work as a journalist and reportedly become engaged.