The prosecutors' move came after a highly controversial review of DNA evidence ordered by the appeals court. The review by two independent experts found that much of the evidence used in the first trial to convict Knox and Raffaele Sollecito was unreliable and possibly contaminated.
The review boosted Knox's efforts to overturn her conviction and be freed after almost four years behind bars. Defense lawyers, opposing the request for new testing, said the prosecutors were simply moaning over a review that had not gone in their favor.
A decision by Judge Claudio Pratillo Hellmann was expected later in the day. If new testing is granted, it would undoubtedly extend the appeals trial, now expected to end in late September.
Knox was convicted in 2009 of sexually assaulting and murdering Meredith Kercher and sentenced to 26 years; Sollecito, an Italian who was Knox's boyfriend at the time, was convicted of the same charges and sentenced to 25 years. Both deny any wrongdoing and have appealed the Dec. 2009 verdict.
In the original trial, prosecutors maintained that Knox's DNA was found on the handle of a kitchen knife believed to be the murder weapon, and that Kercher's DNA was found on the blade. They said Sollecito's DNA was on the clasp of Kercher's bra as part of a mixed trace that also included the victim's genetic profile.
Without a clear motive or convincing witnesses, the DNA evidence is crucial, and much of the appeals outcome hinges on how the court views it.
Prosecutor Manuela Comodi said that the review was "sketchy" and that the experts failed to fulfill their mandate as demanded by the court: retest traces when possible, or else assess the reliability of the testing previously done.
"The experts did not answer the questions posed by the court," Comodi said. "They seeded doubt and said 'everything is possible."'
She contended that they should have retested a "low-copy number" trace found on the blade, especially in light of new machinery that allows for the testing of even smaller amounts than the one found. "Low-copy number" requires fewer human cells than traditional genetic testing methods.
Saying the two experts were "inadequate" and "unreliable," Comodi asked the court to appoint new ones to carry out the new testing.
The experts -- Stefano Conti and Carla Vecchiotti from Rome's Sapienza University -- maintained the DNA quantity on the blade was insufficient for a retest. In other parts of their 145-page report, they alleged glaring errors in evidence-gathering, below-standard testing which they said raised doubts about the attribution of DNA traces, and possible contamination of the evidence.
"Now you have somebody that's corroborated what we've known from the defense side, and the prosecution is unwilling to accept that," said Curt Knox, the defendant's father. "And so now they want a new review, hoping something new will come up, and frankly I don't see that happening."
Comodi also asked the court to put back on the stand a witness who had previously testified that his brother, a fugitive, had killed Kercher during a botched burglary. The witness, a jailed Naples mobster called Luciano Aviello, has contacted the prosecution with a retraction and was questioned in prison on July 2011, Comodi said.
The defense, which had originally put Aviello on the stand, is opposing this request, on the basis that Aviello has proven unreliable.