Records show 'glaring errors' led Italian court to overturn Amanda Knox murder conviction
Amanda Knox talks to the press surrounded by family outside her mother's home in Seattle, Washington on March 27, 2015. Photo by Jason Redmond for Reuters.

Italy's top court threw out a conviction of American Amanda Knox for the 2007 murder of her British flatmate because of "glaring errors" in the case against her, a document showed on Monday.

The brutal stabbing of 21-year-old Meredith Kercher prompted a zigzag of contradictory rulings which ended in March with the acquittal of Knox and her Italian boyfriend Raffaele Sollecito, casting an uncomfortable spotlight on Italy's legal system.

The Court of Cassation said there were no certain biological traces in the room where the murder was committed, nor on the victim's body, of Knox or Sollecito, who have maintained their innocence throughout.

"There was no shortage of glaring errors in the underlying fabric of the sentence in question," the court wrote in the official explanation of its reasons for striking down the second guilty verdict handed to the pair.

The legal meandering which produced two convictions, two acquittals and four years each in jail were due to "deplorable" carelessness right from the start of the probe, the court said.

A kitchen knife found at Sollecito's house and alleged to be the murder weapon was kept in a cardboard box, "the kind that gadgets are wrapped up in for Christmas".

A bra clasp said to have carried DNA evidence was left on the floor for 46 days, possibly trodden on and later passed between people wearing dirty latex gloves.

The third person accused of the murder, Ivory Coast-born Rudy Guede, who is serving a 16-year sentence after opting for a fast-track trial, left "copious" biological traces at the scene, the court said.

The court said avid media attention paid to the killing and the nationalities of the people involved led "a spasmodic search for one or more guilty parties to offer up to international public opinion" which "certainly did not aid the search for the truth".

The decision to overturn the conviction, which called for 28 years in jail for Knox and 24 years for Sollecito, surprised some in Italy who expected the case to be sent back to a lower court.

The court said re-examining it would have been useless as there would be no chance of drawing reliable conclusions from the small amount of evidence available.

It also said the two women's computers, which could have yielded new information, were "incredibly" burned by investigators.

The court upheld a sentence against Knox for falsely accusing Congolese barman Patrick Lumumba of the murder.

(Reporting by Silvia Ognibene and Isla Binnie; editing by Ralph Boulton, Larry King)