PERUGIA, 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.

Sitting on the witness stand with an interpreter next to her, two prison guards behind and her parents at the rear of the medieval courtroom, Knox offered a much different account.

“On November 1, I told Raffaele that I wanted to watch a movie so we went to his place,” said Knox, a University of Washington student who was doing a year abroad. After dinner, they went upstairs to his room, she said.

“I sat on the bed, he sat at his desk, he prepared the joint and then we smoked it together,” the student from Seattle said. “First we made love, then we fell asleep.”

Knox said she had spent time with Kercher at their apartment earlier that afternoon.

They talked about what they had done for Halloween the night before, and Knox said Kercher still had a bit of her vampire makeup on.

She said Sollecito arrived at the house and they had something to eat. Kercher “went to her room to change, she had a shower, I don’t know,” Knox said. “She left her room, said ‘Bye,’ walked out the door. That was the last time I saw her.”

Kercher’s body was found on Nov. 2.

Sollecito, 25, has said he was at his own apartment the night of Nov. 1. He said he does not remember if Knox spent the whole night with him or just part of it. The two have said they could not remember events clearly because they had taken drugs.

Prosecutors planned to cross-examine Knox today.