A knife that prosecutors say could have been used to murder British student Meredith Kercher was shown in court yesterday at the murder trial of her American roommate and an Italian co-defendant.

The knife, wrapped in plastic and kept in a white box, was shown to the eight-member jury in Perugia, 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 for the 2007 death of Meredith Kercher (21).

They deny the charges. The knife was shown as three forensic experts were called by Sollecito's defence to discuss the alleged murder weapon and other evidence they had studied. Prosecutors allege the knife with a six-and-a-half-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 that defence lawyers reject, saying the knife was too big to match Kercher's wounds and the amount of what prosecutors say was Kercher's DNA was too low to be attributed with certainty.

In yesterday'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.

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, she died of combined loss of blood and suffocation.