The knife, wrapped in plastic and kept in a white box, was shown to the eight-member jury in Perugia, in central Italy, during the trial of Amanda Knox and her former boyfriend, Raffaele Sollecito.
Knox and Sollecito, who were in court, watched as the knife was brought in. The two are on trial on charges of murder and sexual violence in the 2007 death of Meredith Kercher. They deny wrongdoing.
The knife was shown as three forensic experts were called by Sollecito's defense to discuss the alleged murder weapon and other evidence they had studied.
Prosecutors allege the knife, with a 6-inch blade, found at Sollecito's house could be the murder weapon. They say it had Kercher's DNA on the blade and Knox's on the handle - a claim defense lawyers reject.
They say the knife is too big to match Kercher's wounds, and the amount of what prosecutors say is Kercher's DNA is too low to be attributed with certainty.
In Saturday's session, forensic expert Mariano Cingolani cast some doubt on the knife's "compatibility" with a wound to Kercher's neck, which is not considered to be the fatal one.
"Many other knives in general are more compatible with that kind of wound," said Cingolani, who was appointed by a Perugia judge before indictments for Knox and Sollecito were handed down.
That conclusion "strikes a hit to the prosecution's case that much further," Knox's father, Curt Knox, told "Early Show Saturday Edition" co-anchor Erica Hill from outside the courtroom.
Knox told Hill he "absolutely" believes his daughter isn't guilty. "She had no part in this crime," he said. "Just pure common sense as it relates to the room (where prosecutors say Kercher was killed) - there's no hair follicle of hers, no blood evidence of her, no DNA whatsoever in that room, and how they can attribute her to this particular crime is beyond me.
" ... I think, as we go through each individual piece of evidence, as the defense has their opportunity to provide their side of the case, it continues to break down the prosecution's theory to this whole crime. And hopefully, we're coming to the end of the journey here and we'll be able to bring her home soon."
Cingolani said one of three cuts on the victim's neck would have been bigger if that knife was used, given the wound's depth. However, the expert also cautioned that no firm conclusion could be drawn without knowing the position of Kercher's neck during the attack or the elasticity of her tissues.
According to Cingolani, whose team did not carry out an autopsy on Kercher's body but examined photos and videos of the procedure, the 21-year-old died of combined loss of blood and suffocation.
He said bruises on her neck suggest she might have been strangled and may have choked on her own blood.
Prosecutors allege that Kercher was killed during what had begun as a sex game. Her body was found in her bedroom in the apartment she shared with Knox on Nov. 2, 2007.