By Maurizio Troccoli

PERUGIA, Italy (Reuters) - Independent forensic experts took the stand on Monday to attack key pieces of evidence used to convict U.S. student Amanda Knox of the murder of her British roommate in the Italian city of Perugia in 2007.

The two court-appointed experts, Carla Vecchiotti and Stefano Conti, told an appeal hearing that the knife thought to have been used to kill 21 year-old Meredith Kercher carried no trace of blood but may have been contaminated with other DNA traces.

Presenting the findings from a report released last month, they said police had used the same gloves to take different pieces of evidence during their initial examination of the house the two women shared in the university town of Perugia.

Kercher was found half naked in November 2007 lying in a pool of blood with her throat cut.

Knox, 24, her former Italian boyfriend Raffaele Sollecito and Ivoirian Rudy Guede were convicted and jailed in 2009 for the murder after what judges concluded was a frenzied sex game that spiraled out of control.

Both Knox and Sollecito, who have appealed against the original ruling were in court on Monday as was Knox's mother, Edda Mellas.

"You know, it was an excellent day, to be able to see everything, step by step exactly what our experts said, you know, and now confirmed by independent experts is very powerful," Mellas told Reuters Television after the hearing.

CONTAMINATION

The report by Vecchiotti and Conti confirmed police conclusions that Knox's DNA was found on the handle of a knife they identified as the murder weapon but said that the material found on the blade was starch, rather than blood.

"There are no scientific elements which would confirm the presence of blood traces on the knife. The protocols for minimizing the risk of contamination were not respected," their testimony said.

They also said there was no DNA evidence on a clip from Kercher's bra which police said was traceable to Sollecito.

The two independent experts had been commissioned by the appeal court to go over the forensic evidence in the case which has attracted huge media interest and severe criticism of police methods from the defense team.

They made a scathing attack on the original investigation, saying that proper decontamination procedures had not been followed, there was insufficient documentation of the amount of DNA evidence collected and inadequate "real time" analysis.

The next hearing is scheduled for July 30 when the experts face cross-examination by prosecutor and the defense team.

Francesco Maresca, a lawyer for the Kercher family, said the evidence provided by Vecchiotti and Conti was not conclusive.

"I hope, I am certain and trust that on Saturday we will be able to clarify in court the fact that they did not follow the original investigation and therefore did not follow the profound exchange of dialogue between various consultants and once again we will remind of the principal factors in this case," he said.

(Writing by James Mackenzie)