On Friday, Ms. Knox appeared in Perugia’s Renaissance-era courthouse to tell her side of the story for the first time. She said she had been yelled at by the police and hit on the head twice while she was being questioned. “They kept calling me stupid,” she added.  Ms. Knox said she had been pressured by the Italian authorities to offer false testimony, in which she accused her boss at a bar where she worked of the crime. In written testimony to the police, she said she had been in the house’s kitchen blocking out Ms. Kercher’s screams as Ms. Kercher was killed by the boss, Patrick Lumumba, originally of Congo.  Ms. Knox said that after hours of questioning, during which the police tried to put ideas in her head, she wanted to write down her testimony to help focus her thoughts. “I wasn’t sure what was my imagination and what was reality,” she said.  Mr. Lumumba was later cleared by prosecutors and is suing Ms. Knox for defamation.  “The declarations were taken against my will, and so everything I said was taken under confusion and pressure,” Ms. Knox said of her written account.  On Friday, Ms. Knox said that she had been at Mr. Sollecito’s house the evening of the crime, where the two smoked marijuana, watched the French film “Amélie” and had sex.  When she returned home the next morning, she said, she noticed the door had been left open, and the door to Ms. Kercher’s room was locked. She said that she and Mr. Sollecito eventually called the police, who found Ms. Kercher’s body.  Four days later, Ms. Knox was arrested. Ms. Knox and Mr. Sollecito are also charged with tampering with the crime scene to make it look like a robbery. If convicted, the two face life in prison.  On Friday, Ms. Knox appeared confident, ebullient and in good humor throughout the daylong hearing. She spoke in both English and fluent Italian, which allowed her to navigate the many hypothetical clauses in her testimony.  In recent weeks, forensic investigators called by the prosecution have testified that they found DNA evidence of Ms. Knox’s footprint in Ms. Kercher’s blood in the apartment, and traces of the two women’s intermingled blood in several places there.  While no definitive murder weapon has been found, the police said an eight-inch kitchen knife at Mr. Sollecito’s house bore traces of Ms. Kercher’s DNA near the tip and Ms. Knox’s near the handle. In addition, a coroner called by the prosecution testified that bruises on Ms. Kercher’s body indicated that she had been held by multiple assailants.  Defense lawyers accuse investigators of shoddy work and tampering with the crime scene.  Ms. Knox was not under oath when she testified. Under Italian law, only witnesses, not defendants, testify under oath.  Sharon Otterman contributed reporting from New York.  A version of this article appears in print on , on Page A4 of the New York edition with the headline: American Student, on Stand in Her Murder Trial in Italy, Claims Police Mistreatment. Order Reprints| Today's Paper|Subscribe
A Seattle college student defended herself against charges that she killed a housemate and accused the Italian police of poor treatment.