In the small bathroom that Knox and Kercher shared, investigators found numerous spots of blood, including on the sink, the toilet, the bidet, the rug, the light-switch and the door jamb. Three of these blood stains – one on the edge of the sink, the one on the drain of the bidet, and one on a Q-tip box - contained the mixed DNA of Kercher and Knox
The significance of the mixed DNA was not explained in court, but in past reports the prosecution has theorized that Knox used that bathroom to wash-up after the murder, and due to a nose-bleed or some other injury, her blood mixed with that of the victim.
Knox's defense, however, has mentioned the possibility that it could be menstrual blood or blood from Knox's ear, which she had recently pierced. Knox had taken a shower in that bathroom the morning after the murder, before Kercher's murder had been discovered.