An Italian judge presiding over the retrial of US student Amanda Knox has ordered new DNA tests on the knife that prosecutors say was used to kill her British roommate in 2007.
Ms Knox and her Italian ex-boyfriend Raffaele Sollecito were found guilty in 2009 of murdering 21-year-old Meredith Kercher.
They were acquitted on appeal in 2011, but the acquittal was later quashed by Italy's supreme court.
Neither Ms Knox or Mr Sollecito appeared in court for the first hearing in the retrial.
Ms Knox, who is now back home in Seattle, has said she will not be returning to Italy.
Judge Alessandro Nencini will also hear new testimony from jailed Naples mafia member Luciano Aviello, who previously said his brother killed Ms Kercher. He is due to appear in court on Friday.
The new checks on the presumed murder weapon - a kitchen knife found in Mr Sollecito's house - will examine a trace that was not previously tested because experts said it was too small to produce reliable results.
The court will also assess photographs of Mr Sollecito's nail-bitten fingers that the defence has presented.
The supreme court overturned the acquittal of Ms Knox and Mr Sollecito in March, citing "contradictions and inconsistencies" and paving the way for the retrial.
Ms Kercher was found with more than 40 wounds, including a deep gash in the throat, in the apartment she shared with Ms Knox in Perugia.
The picturesque town in the central Umbria region attracts students from around the world.
Ms Knox, 26, has denied involvement in the killing. She told US television this month that "common sense" told her not to return to Italy.
She is not obliged to attend the hearing and can be represented by her lawyers, who said she is watching the retrial closely from her home in Seattle.
Mr Sollecito, 29, who has also protested his innocence, plans to attend some of the hearings, his father Francesco said, adding he was confident his son's innocence would be confirmed.
Ivory Coast-born Rudy Guede is serving a 16-year sentence for Ms Kercher's murder.
