PERUGIA, Italy —A prosecutor in the Amanda Knox appeal hearing Saturday challenged forensic experts who have said evidence used to convict the American student of the slaying of her British roommate in 2007 is unreliable.
The experts, Carla Vecchiotti and Stefano Conti, said they found no evidence to support original police conclusions that the blade of the knife thought to have been used to kill 21-year-oldMeredith Kercher carried traces of the victim's blood.
Knox, 24, her former Italian boyfriend Raffaele Sollecito and Ivorian Rudy Guede were convicted and jailed in 2009 for murder after what judges concluded was a frenzied sex game that spiraled out of control.
Prosecutor Manuela Comodi questioned the details of the independent experts' report on Saturday, asking, for example, if they could be sure there was noDNA on the blade just after Kercher's death.
Vecchiotti said they could not exclude that possibility, but said "on the basis of the tests we have done today there are no traces ofDNA," and added the original procedures used were not reliable.
She said the knife had not been handled or cleaned properly in the initial investigation, and could have been contaminated with other DNA traces.
Vecchiotti and Conti's report released last month confirmed police conclusions that Knox's DNA was found on the handle of a knife they identified as the murder weapon but said the material found on the blade was starch rather than blood.
Francesco Maresca, a lawyer representing Kercher's family, said the explanation given by the experts on Saturday was not sufficient to be able to reevaluate the evidence, but Knox's mother, Edda Mellas, said the appeal was going well.
"Today even though the prosecution tried to make confusion, the experts are sticking by their report," Mellas said.
Both Knox and Sollecito, who have appealed against the original ruling, were in court on Saturday. Knox, who wore a pink cardigan and smiled at times, has been described by her mother as "thrilled" by the latest forensic report.
The two experts had been commissioned by the appeals court to go over the forensic evidence in the case, which has attracted huge media interest and severe criticism of police methods from the defense team.
The trial is set to resume in September after a break for the summer.
In the report, the experts said proper decontamination procedures had not been followed in the initial investigation, there was insufficient documentation of the amount of DNA evidence and inadequate "real time" analysis.
The court heard a letter on Saturday from scientific police director Piero Angeloni, defending the work of the original forensic team.