PERUGIA, Italy-- A police forensic expert who conducted the original investigation in the Amanda Knox case insisted Tuesday that there was no contamination on crucial pieces of evidence linking the American student and her co-defendant to the murder of her British roommate.
Patrizia Stefanoni examined DNA traces in the aftermath of the 2007 killing of Meredith Kercher in Perugia. But her work was criticized by independent experts appointed by the court to review the evidence. They have 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.
Knox and Raffaele Sollecito were convicted of sexually assaulting and killing Kercher in the apartment that Knox and the 21-year-old Briton shared while studying in Perugia. Knox was sentenced to 26 years in prison; Sollecito to 25. Both deny wrongdoing and have appealed the December 2009 verdict.
Debate over DNA evidence has taken the center stage at the appeals trial, with genetic experts taking the stand in the frescoed courtroom in Perugia. A verdict is expected by month's end.
Detailed explanations of DNA extraction techniques and genetic science -- often performed with slides in a dimly-lit, hot courtroom -- have sorely tested the attention spans of many attendees.
Knox herself appeared to nod off for a second, at one point apparently closing her eyes and her head falling forward.
Even Presiding Judge Claudio Pratillo Hellmann joked about it Tuesday.
"I'm glad to see you have no slides," he said with a wry smile as a geneticist was taking the stand -- only to have his hope dashed.
In testimony spread over two days, Stefanoni has rejected accusations of shoddy forensics work.
On Tuesday, she told the appeals court that she could rule out contamination on a kitchen knife believed to be the murder weapon and on the clasp of Kercher's bra -- both key pieces of evidence in the case.
In the original trial, prosecutors maintained that Knox's DNA was found on the knife's handle and that Kercher's DNA was found on the blade. They say 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.
Stefanoni said the knife, found at Sollecito's house, was tested in a lab six days after the investigators had analyzed a trace of Kercher's DNA -- excluding contamination.
The bra clasp was also controversial because it was recovered off the floor at the crime scene 46 days after the killing. The independent review said that the "context ... was highly suggestive of ambient contamination."
room was brought inside." She insisted that out of 133 specimens analyzed in the house of the murder -- including 89 in Kercher's room -- Sollecito's genetic profile was only found in a cigarette butt in an ashtray, mixed with Knox's.
"If Sollecito's DNA had somehow traveled from the butt to the clasp, then there would be Knox's DNA as well on the clasp," she said.
However, defense lawyers pointed out that the clasp, when collected, was a few feet away from where it was originally seen in a crime scene police video.
"It was moved by somebody, we don't know how, and it's possible that it was turned upside down," said Adriano Tagliabracci, a genetic expert who took the stand Tuesday for the defense.
"How can we be certain that that is a reliable exhibit?"
one hour late as some members of the jury were stalled due to a national strike affecting transportation.