Italy ? An American college student accused of murdering her British roommate in Italy testified for the first time on Friday, offering an alibi for the night of the 2007 killing and saying police beat her into making a false statement in the case.

Amanda Knox, 21, said she smoked pot, had sex with her boyfriend — co-defendant Raffaele Sollecito — and fell asleep at his apartment on the night of the slaying. She said she did not return home until after her roommate was killed.

Knox alternated between fluent Italian and English during roughly six hours of testimony in a packed Perugia courtroom, where she is being tried on charges of murder and sexual assault for the slaying of 21-year-old Meredith Kercher, a British student.

Knox’s account of the night of the murder contrasts with that of prosecutors, who say Kercher was killed during what began as a sex game.