Italian Police are investigating claims a man was threatened with a knife by a suspect in the Meredith Kercher case, 24 hours before the student was killed.
Meredith Kercher was from Coulsdon in south London
The man is reported as saying Amanda Knox, Miss Kercher's flatmate, was with the two other suspects when she waved a knife at him after he crashed his car.
Raffaele Sollecito and Rudy Guede claim they have never met each other.
All three deny killing the 21-year-old Leeds University student, from south London, who was found dead in November.
Miss Kercher, 21, from Coulsdon, was living in Perugia at the time.
In police statements leaked to the Italian media, the Albanian man said he had been too scared to come forward sooner but now realised the importance of his testimony.
He was reported as saying after he crashed, he saw Mr Sollecito and Ms Knox start to shout.
"We began to argue and the girl drew out a knife. She shouted at me and pointed it at me," he reportedly said.
Lawyers for Mr Guede dismissed the new witness as a "fantasist".
The suspects have been held at Capanne Prison, near Perugia, for more than two months. They can all be held for up to a year before trial.
Earlier this month, police found the outline of a bloody footprint in Amanda Knox's bedroom.