PERUGIA, Italy - An Ivory Coast man already convicted of killing the British roommate of Seattle student Amanda Knox broke into a nursery school and stole a big knife two weeks before the murder, a new witness testified.

The witness, who owns a nursery school in Milan, Italy, took the stand Saturday in the murder trial of Knox and her former Italian boyfriend, Raffaele Sollecito. The two are accused of killing Meredith Kercher in November 2007.

The nursery school owner was the latest defense witness to describe bizarre or suspicious behavior by Rudy Guede of Ivory Coast before the murder of Knox's roommate, Meredith Kercher. Her testimony helped bolster the defense's contention that Guede killed Kercher - not Knox.

The witness said Guede broke into her nursery school and spent the night there in October 2007.

"When she found him in her nursery school, he looked totally nonplussed that she had caught him there," said ABC News reporter Ann Wise, who is covering the trial.

"And when she called the police, they came and searched his bag and found a stolen computer and a stolen cell phone and a big kitchen knife he had stolen from the nursery school."

On Friday, a lawyer testified that he was robbed just days before the murder by Guede - who was sentenced to serve 30 years for Kercher's murder in a fast-track trial last year.

The lawyer told the court he found the window to his studio broken by a large rock, and was missing a computer and printer.

According to earlier testimony, there was a window in the house where Kercher was killed - and it also was broken with a big rock.

"What the defense is trying to show is that (Guede) was a thief who had broken into places a number of times. He also had threatened someone with a knife," Wise said.

"So they're really trying to, let's say, put the blame on Rudy Guede and take it off Amanda and her boyfriend. And since this guy is sort of an unreliable drifter, it's not a difficult chore."

The defense theory is that Rudy Guede broke in to Knox and Kercher's home to steal something, found Kercher there, and ended up killing her. But Guede denies wrongdoing and has appealed his conviction.

Prosecutors allege that Kercher was killed by Knox and Sollecito with a knife to the throat during what had begun as a sex game. Her body was found in the apartment she shared with Knox on Nov. 2, 2007.

Also on Saturday, a longtime Seattle friend of Knox's told the court that she was very conscientious, had worked hard to get to Perugia and that she loved music and sports.

The friend, Madison Paxon, was asked about Knox's drug use, and she testified that Knox rarely smoked marijuana - perhaps two or three times a month at most.

Paxon also said that Knox had come to Perugia to immerse herself in Italian culture, and she also said that Knox had told her that she got on very well with her roommates in Perugia.