A bloody footprint found at the house where a British student was killed in Italy was wrongly attributed to one of the defendants in the case, a forensic expert for the defense testified at the murder trial Friday.

The footprint was found on a bathroom rug in the house in Perugia, central Italy, where Meredith Kercher was killed in November 2007. Prosecutors and police scientists have attributed the print to Raffaele Solicit, an Italian who is on trial on murder charges with American student Amanda Knob, his girlfriend at the time.

Both defendants deny wrongdoing.

In his testimony, expert Francesco Vinci compared detailed pictures of the footprint on the rug with images of Sollecito's feet, arguing that the sizes and shapes "absolutely don't match."

"Differences, one by one, can be seen," said Vinci, who was called by Sollecito's defense team.

The images showed what were described by Vinci as differences between the shape of toes and the ball of Sollecito's right foot and those of the bloody footprint.

Prosecutor Giuliano Mignini insisted during a break in the proceedings that such discrepancies could have an explanation.

"It could be that the foot's sole was not completely covered in blood," and the print could be the result of pressure from only part of his foot, the prosecutor said.

According to Vinci, the footprint was "compatible" with the foot of a third defendant, Rudy Hermann Guede, who was convicted in a separate trial last year and sentenced to 30 years in prison.

Guede, of the Ivory Coast, denies wrongdoing and has appealed his conviction.

The expert said he participated in one of the crime scene investigations by forensic experts at the murder scene.

Vinci said he also examined a blood trace left on Kercher's mattress sheet, which he said came from a knife with a 3 1/2-inch-long blade that was placed on the bed.

His contention contrasts with prosecutors' allegations that a 6 1/2-inch knife found at Sollecito's house matched the victim's wounds and might be the murder weapon.

Prosecutors say the knife had Kercher's DNA on the blade and Knox's on the handle, but defenses have argued that traces of the victim's DNA are too low to be attributed with certainty.

Knox and Sollecito could be sentenced to life imprisonment if convicted.

On Saturday, the knife that prosecutors say could be the murder weapon is expected to be shown in court.

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.

The house, which has been broken into by intruders in recent months, has been fixed up and is now available for rent, said Letizia Magnini, a lawyer representing the owner.