Amanda Knox, along with Raffaele Sollecito, was definitively cleared of killing Meredith Kercher earlier this year, but only after a long fight that had at its heart the ability of forensic science and the judiciary to know what to ignore.
On the day of the murder in 2007, police collected many samples from the room where Knox’s housemate Kercher died. Knox and then boyfriend Sollecito were held on the basis of the prosecutor’s gut instinct, but when fingerprints and DNA from the scene were analysed, only two profiles were identified: those of the victim and Rudy Guede, a man known to police. He was convicted of murder, but the prosecutor still pursued Knox and Sollecito.
One piece of evidence emerged as crucial: a kitchen knife at Sollecito’s house. It didn’t match many wounds on the body and tested negative for blood. DNA from Knox was on the handle – she had cooked with it. But on one swab from the blade, a minuscule trace of DNA was detected, just once during many analyses. It had some that was consistent with the victim’s. This finding was never repeated, despite many attempts. The debate was about whether or not that single result was reliable.
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