Prosecutors rejected claims Monday that police contaminated evidence used for its case requesting an American woman and her former Italian boyfriend stand trial for killing a British student.

The prosecution closed its arguments Monday at the courthouse in Perugia, central Italy, and a judge is expected to rule Tuesday whether Amanda Knox and Raffaele Sollecito will go on trial for the killing.

Meredith Kercher, a 21-year-old student from Leeds University in England, was found dead in her bedroom Nov. 2 from a stab wound to the neck. Prosecutors say she was killed while an unwilling participant of a sex game.

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They also asked that a third suspect, Rudy Hermann Guede of Ivory Coast, be sentenced to life. Guede is undergoing a fast-track trial at his request. All suspects deny wrongdoing.

Prosecutors claim that key evidence linking Sollecito to the death is from his DNA found on the victim's bra.

But Sollecito's defense says that multiple DNA traces were found on the bra — not just from one person — suggesting the evidence was inadvertently contaminated by police.

"This is not a genetic trace belonging to one single person but it's a mix, a combination resulting from contamination, obviously involuntary, and therefore should not be admitted as evidence in court," one of Sollecito's lawyers, Giulia Bongiorno, said. She cited an examination by a defense team expert.

Prosecutor Manuela Comodi said Monday that "we gave a substantially different interpretation on the same elements" than the defense, including the bra.