Amanda Knox DNA expert defends evidence

The 24-year-old from Seattle, who has been behind bars since November 2007, was relieved to be back in court after the summer break (AP)

The forensic expert whose evidence helped convict Amanda Knox of murdering British student Meredith Kercher today defended her work after a review criticised her methods.

Patrizia Stefanoni spoke at Knox's appeal trial which resumed after a summer recess. A verdict is expected by the end of the month.

American Knox and her co-defendant and former boyfriend, Raffaele Sollecito, were convicted of sexually assaulting and killing Meredith Kercher in the Perugia apartment that Knox and 21-year-old Miss Kercher, from Coulsdon, Surrey shared while studying in Italy.

Knox was sentenced to 26 years in prison; Sollecito to 25.

An independent review of DNA traces in the case found that much of the evidence collected in the original investigation fell below international standards and may have led to contamination of the samples.

They especially focused on some traces of DNA linking the defendants to the crime, and concluded that due to the risk of contamination and the low amounts of DNA used for the testing it was impossible to extract a genetic profile with any certainty.

Prosecutors had said that Knox's DNA was found on a knife handle and Miss Kercher's DNA was found on the blade. They also say Sollecito's DNA was found on the clasp of Miss Kercher's bra.

Independent expert Carla Vecchiotti told the hearing today that data was so mixed that a very high number of genetic profiles could be extracted, depending how one combined the data.

"I could find yours, too," Ms Vecchiotti told the presiding judge. "I'm there, too," she said, adding that some data was compatible with her own DNA. She said Miss Kercher's profile was the only certain one.

The findings have boosted the defendants' efforts to be cleared and gain freedom after almost four years in prison.

But Ms Stefanoni, the forensic police officer, countered some of the points, saying that DNA analyses were carried out from behind a glass wall to avoid the risk of contamination. She also said some of the standard protocols cited by the experts were published after she finished her report in May 2008.

Just before the trial resumed, Miss Kercher's sister issued a letter asking the appeals court to assess "every single (piece) of evidence" so justice can be done. The Kercher family insisted they still had faith in the Perugia police, investigators and the court, but also expressed worry over the evidence review.

"We find it extremely difficult to comprehend how the evidence that was so carefully developed and presented in the first hearing was valid, yet how it now seems to carry a slight chance it will become irrelevant," Stephanie Kercher said in the letter.

"We ask that the Court of Appeal assess every single (piece) of evidence, both scientific and circumstantial, as well as any witnesses who have taken the stand independently of any other information or media," she wrote.

The Kercher family has kept a low profile throughout the high-profile case. The letter, released through the family's lawyer Francesco Maresca, represented a rare break in their silence.

"Meredith has been forgotten because she is no longer with us, yet this should be about her and what really happened on that tragic evening," Stephanie Kercher lamented in the letter.

Knox, a student from Seattle, has been the centre of attention since her arrest on November 6, 2007 - four days after Miss Kercher's body was found.

A third person, Rudy Hermann Guede of the Ivory Coast, has also been convicted of Miss Kercher's murder in a separate hearing.

AP