PERUGIA, Italy — An American student accused of murdering her British roommate in Italy had a growing hatred for the victim and killed her in retaliation during a drug-fueled sex game, a prosecutor said Friday in closing arguments at her murder trial.

Lead prosecutor Giuliano Mignini argued that Amanda Knox, together with her ex-boyfriend and co-defendant Raffaele Sollecito and a third man convicted in a separate trial last year, killed Meredith Kercher under "the fumes of drugs and possibly alcohol" and then tried to cover up their crime by staging a burglary.