A state prosecutor urged Italy's top court to overturn the acquittal of American Amanda Knox and a former boyfriend for the murder of British student Meredith Kercher.
Mr Kercher's half-naked body, with more than 40 wounds and a deep gash in the throat, was found in the apartment she shared with Ms Knox in Perugia in 2007.
The Court of Cassation, Italy's final court of appeal, is due to decide today or tomorrow whether to start the process for a retrial or to uphold the 2011 verdict and close the case definitively.
"In this trial the judge lost his way," state prosecutor Luigi Riello told the court, urging it to accept the request for an appeal from Perugia prosecutors and Kercher family lawyers, who say the verdict was flawed and left central aspects of the case unexplained.
Both Ms Knox's lawyer Luciano Ghirga and Giulia Bongiorno, a lawyer for Ms Knox's former boyfriend Raffaele Sollecito, said they were confident the court would uphold the verdict clearing their clients of murder.
Prosecutors accused Ms Knox and Mr Sollecito of killing Kercher in a drug-fuelled sexual assault.
They were initially found guilty and sentenced to 26 and 25 years in prison respectively after a trial that grabbed headlines all over the world.
In 2011, their convictions were overturned and they were released after serving four years in prison.
"We all still miss Meredith terribly," her sister Stephanie said in a statement. "A beautiful young girl, my little sister, was taken from us far too soon in such a brutal way with too many unexplained factors."
The ruling, which will be made on procedural issues, not on questions of merit, could be the last development in a case whose initial handling was sharply criticised by independent forensic experts.
"There seems to be very little criticism of the technical aspects of the trial," said Mr Ghirga.
Prosecutors last year filed a motion to appeal against the acquittals, calling the verdict "contradictory and illogical".
Francesco Maresca, a lawyer representing Ms Kercher's family, said in a statement the acquittals had been "defective" and "lacked transparency".
"There was a lot of external pressure and the judge showed a will from the start to acquit," Mr Maresca said.
If the Court of Cassation upholds the request and decides to go back to trial, new hearings will be held at a later date.
However, Mr Bongiorno said there was little room for the decision to be challenged.
"We have a verdict behind us that is so well-grounded, coherent and logical that we're very calm," she said as she entered the court.
Italian law permits prosecutors to appeal against not guilty verdicts.
The Court of Cassation will decide whether there were any procedural irregularities that give grounds for a retrial, rather than examining the facts of the case.
Ms Knox and Mr Sollecito were acquitted after the independent forensic investigators challenged police scientific evidence.
A third man, an Ivorian drifter named Rudy Guede, was found guilty and sentenced to 16 years in a separate trial.
He is now the only person serving time for the murder, although prosecutors say he could not have killed Ms Kercher by himself.
Ms Kercher, a student at Leeds University, was 21 when she died.
Ms Knox, dubbed "Foxy Knoxy" in many early media reports, was initially portrayed as promiscuous and dishonest but a lobbying campaign by her family helped change perceptions.
She returned to her Seattle-area home after she was released from prison in Italy and is scheduled to speak publicly about the trial for the first time on American television in April, when her book of memoirs is also due to be released.