On the eve of a fateful summer journey to Italy, the American student Amanda Knox drew up a list of things to do before she left home in Seattle. Top of the list, according to her diary, was visiting a sex shop.

A book published in Italy last week quotes leaked extracts from Knox’s diary and portrays her as a young woman for whom sex is a key part of life. Knox, 21, will go on trial in January along with her Italian ex-boyfriend Raffaele Sollecito, 24, accused of sexually abusing and murdering the Leeds exchange student Meredith Kercher in November 2007.

Kercher, 21, stabbed in the throat, was found half-naked in her bedroom in the Perugia cottage she shared with Knox. Rudy Guede, 21, an Ivory Coast drifter, has already been jailed for 30 years for the crime. All three pleaded not guilty.

The book, Amanda and the Others by Fiorenza Sarzanini, a journalist on Italy’s Corriere della Sera newspaper, quotes previously unpublished extracts from diaries Knox kept from August 2007 until a few weeks after the murder. They have been seized by investigators.

Knox’s family protested at the publication of “Amanda’s personal and private property” and said they had no means to judge their authenticity.

“This seems to be yet another example of the continued leaks designed to harm Amanda’s character as there is no evidence to tie her to the brutal and senseless murder of Meredith Kercher. She is innocent,” they said in a statement.

Sarzanini said yesterday: “Knox isn’t obsessed with sex but she sees it as one of the predominant aspects of her life. This has influenced her life in the sense that it influences her relationships with both men and women.”

Before leaving Seattle, Knox, who is fond of making lists and called herself Foxy Knoxy, wrote that buying condoms was one of her priorities. On October 18, 2007, she lists four men with brief descriptions, including an American boyfriend.

Sarzanini comments: “It’s as if you [Knox] were always hunting men. You list your conquests as if you were displaying them like trophies.”

Knox writes to one boyfriend: “I’m waiting for you, I want to see something porno with you and put it into practice with you.” In another list, Knox names four men in Seattle and New York, and three in Florence and Perugia with whom she has had sex.

Knox writes: “Interesting isn’t it? I think it means that my sex life doesn’t correspond to my romantic emotional life. An obvious statement because the only one I’m in love with (even if in truth he isn’t the only one I want to have sex with) is incredibly far away . . . Sex is useless, well not useless but always disappointing unless I manage to establish emotional contact with someone.”

The book quotes testimony to police from Amy Frost, a British student friend of Kercher. She describes an episode on the day of Knox’s arrival at the cottage: “Meredith told us that Amanda put down in the bath-room a beauty-case in which there were condoms and a vibrator. They were visible and it seemed a bit strange to Meredith.” Kercher later told Frost: “Isn’t it odd that a girl arrives and the first thing she shows is a vibrator?”

In a sign of tension between Knox and the victim, Frost also relates that a few weeks before the murder Kercher had learnt from her housemates that one of them, Giacomo Silenzi, fancied her. When Kercher told Knox, she replied: “I like Giacomo too, but you can have him!” The remark upset Kercher, who later started a relationship with Silenzi.

Several witnesses quoted in the book depict Knox and Sollecito as not only failing to show any grief immediately after Kercher’s death, but also constantly cuddling and kissing as they sat waiting to be questioned at police headquarters, a few days before they were accused of the crime. “[Amanda] was in front of Raffaele. I remember that she stuck her tongue out at him, she made faces and then they’d laugh and kiss each other. In that moment I thought she was going crazy, that she was really crazy,” Frost testified.

Robyn Butterworth, a British friend of Kercher who saw Knox at police headquarters, gave evidence that Knox “seemed to me to be completely lacking any emotion”. Butterworth added that Knox and Sollecito “sent each other kisses by smacking their lips. At a certain point she stretched out on a few chairs and he caressed her feet. It was strange, it wasn’t a nice thing to watch”.

Prosecutors have argued that Knox’s alleged coldness after the murder, as well as her DNA on the handle of a knife that may be the murder weapon, points to her guilt. Knox’s parents have said Knox was in shock and was simply seeking comfort from her boyfriend.

In another diary that Knox started in prison on November 8, 2007, shortly after her arrest, there is a rare passage about Kercher in which she imagines her raped and killed.

She wrote: “I can only imagine what she felt in those moments frightened, injured, raped. But I imagine more what she went through when the blood went out of her. What did she feel? And the mother? Desperation? Did she have the time to find peace or in the end did she have only terror?”

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