The retrial of Amanda Knox is underway in Florence - for the murder of her 21-year-old British roommate - Meredith Kercher.

The Seattle native who's case has become an international sensation - spent four years in jail - after an Italian court convicted her and her ex-boyfriend Raffaele Sollecito of killing Kercher in what was described as a drug-fuelled sexual assault.

Then, in a dramatic reversal, the two were released from prison on appeal in 2011.

But, in March, the Italian supreme court overturned these acquittals - citing "contradictions and inconsistencies" - and paving the way for a new appeals trial.

26-year-old Knox will not return to Italy for the proceeding - while Sollecito is expected to attend some of the hearings.

In court on Monday, Sollecito's lawyer demanded more testing of the crime scene.

SOUNDBITE: Raffaele Sollecito's lawyer Giulia Bongiorno, saying (Italian):

"The room is the crime scene and seeing as that room was filled with traces of Rudy Guede and the victim and as the prosecution have said that Amanda Knox and Raffaele Sollecito cleaned that room we demand further forensic tests to see if this selective cleansing is possible."

Ivory Coast born Rudy Guede was found guilty of Kercher's murder - and currently is serving a 16-year sentence - but in calling for a retrial - ithe court said he could not have acted alone.

Knox - who has maintained her innocence - will be represented in court by her attorneys.