By Lydia Warren A woman whose ex-boyfriend is on trial for raping and murdering a student claimed in a video shown to the court that she sat on the victim's face for up to 15 minutes during bondage play - in what has come as a shocking twist in the already sordid case. The chilling video, which was filmed by public defenders days after her then-boyfriend Seth Mazzaglia was arrested, throws doubt on claims made by the prosecutions' key witness Kathryn McDonough, who previously told the court that she had not had any sexual involvement with Lizzi Marriott. Mazzaglia's defense team just needs to convince one juror in the Dover, New Hampshire courtroom that McDonough, 20, is lying to spare him a first-degree murder conviction.
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The video filmed by a public defender in October 2012 shows Kathryn McDonough acting out how she sat on Lizzi Marriott the week before
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The shock footage comes after McDonough told the court she had not had any sexual interaction with the 19-year-old student before her death
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McDonough, the prosecution's key witness, claimed she was protecting her boyfriend - but her inconsistencies throw doubt on her testimony
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Her ex-boyfriend Seth Mazzaglia is charged with the first degree murder
not find her credible, @placeholder could walk away from the trial without