The experts had been appointed by an Italian appeals court to review the DNA evidence used in Knox's trial, including some found on a kitchen knife believed to be the murder weapon and some found on the clasp of the victim's bra.
That evidence played a crucial role in securing the convictions of Knox and her co-defendant Raffaele Sollecito in the 2007 murder of Meredith Kercher, a Briton who shared an apartment with Knox while they were both exchange students in the city of Perugia.
Knox, 24, and Sollecito, 27, have denied wrongdoing and have appealed. The evidence review was granted at the request of their defense teams.
In the first trial, prosecutors maintained that Knox's DNA was found on the handle of the kitchen knife and Kercher's DNA was found on the blade. They say Sollecito's DNA was found on the clasp of Kercher's bra.
But the independent experts told the appeals court that the collection of evidence fell below international standards and may have resulted in contamination. They used slides to refer to international protocols for the collection and sampling of evidence, including one from the U.S. Department of Justice and others from various U.S. states.
One of the two experts, Stefano Conti, cited several cases of forensic police entering the crime scene or coming into contacts with objects there not wearing protective equipment such as masks or hair caps. He said that while evidence should be wrapped in paper or kept in a paper bags, police often used plastic bags, heightening the risk of contamination.
"There are various circumstances do not adhere to protocols and procedures," the forensic expert told the court.
In footage and framegrabs shown to the court, two police officers collected the bra clasp, and the glove worn by one of the two appeared to be dirty on two fingers. Conti noted the bra clasp was collected 46 days after the Nov. 1, 2007 fatal stabbing of the 21-year-old Kercher.
"Over those 46 days several objects were moved, and in at the same time several people will have come in and out," he noted, again stressing the risk of contamination.
The other expert, Carla Vecchiotti, explained to the court that the genetic profile on the knife's blade that was attributed to Kercher is dubious and cannot be attributed with certainty. She said the original testing did not follow recommendations of the international scientific community for dealing with DNA testing.
Vecchiotti said 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 independent experts, both from La Sapienza University in Rome, will be questioned and cross-examined in the next hearing, scheduled for Saturday. That will be the last hearing before the summer break.
The full review, a 145-document obtained by The Associated Press, was filed to the Perugia court last month.