Amanda Knox Trial: DNA Expert Takes Stand in Support of Knox

Sept. 28, 2009 — -- After months of hearings and more than 100 witnesses, the final witnesses took the stand in the Amanda Knox trial over the weekend in Perugia, Italy.

Knox, an exchange student from Seattle, is accused, along with her former Italian boyfriend Raffaele Sollecito, 25, of sexually assaulting and killing British student Meredith Kercher, 21, with whom Knox shared a cottage on the outskirts of the picturesque Italian hill town.

Among the final witnesses was Sarah Gino, a DNA expert called by Knox's defense team, who took aim at the kitchen knife prosecutors believe was used to murder Kercher.

Prosecutors say Knox's DNA was found on the knife's handle, and that her roommate Kercher's DNA was found on the blade.

But Gino told the court that the DNA taken from the knife was too miniscule to be reliable and that the knife easily could have been inadvertently contaminated.

Gino also said the prosecution provided amplified DNA samples that were missing dates. She called the DNA amplification -- the process of copying a small DNA sample to examine it -- the "key moment" in DNA analysis.

The dates are important, Gino said, "because they would tell us what samples were tested together on the same day, which might indicate if some of them could have been contaminated."

She said dating the procedure for each sample was important to ensure that the amplification did not happen twice by mistake.

"DNA does not have wings, but it flies," she said about the possibility of contamination in the police lab. "In a laboratory, where hundreds of samples are examined, the risk of contamination exists and should be taken into consideration."