Traces of DNA on a knife allegedly used as a weapon to murder British student Meredith Kercher cannot be linked "for certain" to American student Amanda Knox, court-appointed experts in Italy said Wednesday, reported dpa.
"International procedures in relation to ... the gathering of evidence at the (crime) scene were not followed," the experts said in a report submitted to judicial authorities.
"Given that none of the recommendations made by the international scientific community relative to the handling of samples were followed ... it is not possible to agree with attributing for certain" the DNA to Knox, the experts wrote.
The findings could prove decisive in an ongoing appeals trial for Knox, 23, and her former boyfriend and co-accused in the 2007 murder, Italian Raffaele Sollecito, 27, news reports said.
Knox and Sollecito received jail sentences of 26 and 25 years respectively after being convicted in 2009 of killing the 21-year-old Kercher.
The British student's half-naked body was found with the throat slit in the Perugia house she shared with Knox.
Both Knox and Sollecito deny any wrongdoing and their appeal trial centres on what their lawyers maintain is disputed DNA evidence relating to the knife and also a metal clasp from Kercher's bra, which allegedly contained traces of Sollecito's DNA.
In the report submitted Wednesday, the experts also cast doubt on the scientific validity of the DNA traces on the clasp, noting how "environmental contamination" may have distorted the results of the initial tests.
On Monday, a third person convicted of killing Kercher, Ivory Coast-born Rudy Guede, confirmed his previous accusations against Knox and Sollecito, saying the couple had been at the Perugia house the night Kercher was killed.
Guede, who had opted for a separate, fast-track trial, was in 2008 sentenced to 30 years in prison for sexually assaulting and murdering Kercher.
His sentence was subsequently reduced to 16 years on appeal.
The trial in Perugia, a picturesque and normally tranquil central Italian university town, has attracted huge international media attention, particularly from the US and Britain.