Amanda Knox lawyers: DNA could overturn verdict

Updated 4:43 p.m. ET

ROME - Amanda Knox won a crucial legal victory Wednesday as an independent forensic report said that much of the DNA evidence used to convict the American student and her co-defendant in the murder of her roommate is unreliable and possibly contaminated.

The review's findings that DNA testing used in the first trial was below international standards will undoubtedly boost Knox's chances of overturning her murder conviction.

The review by the two court-appointed independent experts had been eagerly awaited: With no clear motive for the brutal murder of Meredith Kercher and contradicting testimony heard in court, the DNA evidence was key to the prosecution's case.

Knox was convicted in 2009 of sexually assaulting and murdering Kercher — a Briton with whom she shared an apartment while both were exchange students in Perugia — and sentenced to 26 years in prison. Her co-defendant and ex-boyfriend Raffaele Sollecito was also convicted and sentenced to 25 years.

Both have denied wrongdoing and are appealing. A verdict in the appeals trial is expected in the fall.

Knox, a 23-year-old from Seattle, was "very happy" to hear about the review, her mother said.

"She's breathing for the first time in years," Edda Mellas told The Associated Press. But, she added, "We're not celebrating until Amanda walks out of jail."

Prosecutors maintained in the first trial that Knox's DNA was found on the handle of a kitchen knife they believe to be the murder weapon, and that Kercher's DNA was found on the blade. They say Sollecito's DNA was found on the clasp of Kercher's bra.

Those findings were disputed by the defense, and the appeals court granted an independent review at their request. A similar attempt by Knox's defense had been turned down in the first trial.

The independent experts say in the report filed to the Perugia court on Wednesday and obtained by the AP that the genetic profile attributed to Kercher is "unreliable" and cannot be attributed with certainty.

They said results may have been contaminated on both the blade and bra clasp.

Regarding the blade, the experts said: "We believe that the technical tests are not reliable."

The experts also said the original testing did not follow any of the recommendations of the international scientific community for dealing with "low-copy number" DNA testing, which requires fewer human cells than traditional genetic testing methods.

They also said that "international procedures for inspection and international protocols for gathering and sampling exhibits have not been followed."

"It cannot be ruled out that the result obtained ... may stem from contamination," according to the 145-page report.

The experts reached similar conclusions regarding the bra clasp. The bra was recovered off the floor of the crime scene only several weeks after the Nov. 1, 2007 fatal stabbing of the 21-year-old Kercher.

"The exhibit was retrieved 46 days after the crime, in a context that was highly suggestive of ambient contamination," the report said.

The experts also said the original testing did not follow any of the recommendations of the international scientific community for dealing with "low-copy number" DNA testing, which requires fewer human cells than traditional genetic testing methods.

They also said that "international procedures for inspection and international protocols for gathering and sampling exhibits have not been followed."

"It cannot be ruled out that the result obtained ... may stem from contamination," said the report's conclusions, obtained by CBS News.

However, the review concurred with the original testing in saying that the genetic profile on the knife's black plastic handle could be attributed to Knox. The knife was found at Sollecito's apartment.

The defense had long maintained DNA traces were inconclusive and that they might have been contaminated when they were collected and analyzed.

"We've been waiting for three years for this," Knox attorney Luciano Ghirga said. "It finally came."

The two experts — Stefano Conti and Carla Vecchiotti from Rome's Sapienza University — will present their review in court July 25. Then, the court will hear forensic consultants for the prosecution and for the Kercher family, who is part of the trial as civil plaintiffs.

"We are surprised and stunned by such a categorical judgment," said Francesco Maresca, the Kerchers' lawyer, adding that the forensic experts who carried out the original testing were serious professionals. He said he would seek en explanation for "such drastic conclusions."

The independent experts had been assigned to either conduct a retest or, if not possible, assess the accuracy of the original testing. They began their review in February and soon found that DNA traces were too small for a retest. So, they moved on to reviewing the original analyses to assess whether they were reliable and up to standard.

Initially given about three months to conclude their report, they sought and were granted an extension of about 40 days.