A defense consultant has testified at the Amanda Knox murder trial in Italy, casting doubt on the prosecution's case against the former University of Washington student from Seattle.

An Italian news agency says a coroner, Carlo Torre, testified Monday that a knife believed to have been used to kill her British roommate is not compatible with the victim's stab wound.

The ANSA news agency says Torre testified the wound was made with a knife with a 3-inch blade. Prosecutors say the murder weapon is a knife with 6 1/2-inch blade found at the home of Knox's boyfriend at the time, Raffaele Sollecito's (sol-EH'-chee-toh).

Torre also testified there is no evidence that Meredith Kercher was assaulted by more than one person.