Oh please, the knife is the single most incompetent part of this entire case. So the cops turn up and find a murder by stabbing. So what do they do. Do they carefully collect every single knife or stabbing instrument, scissors, letter openers, etc in the house, carefully bag them and then run a dna test on all of them to find the weapon. NO They leave all the knives in the house, cross the road, go to Sollecito's apartment, take one random kitchen knife because their "Intuition tells them its the right one. The only knife they take. and test that one, only that one and then find Amanda's DNA on the handle and claim Meredith's dna is on the blade. Wow, what incredible luck. Just think, of all the knives they don't bother to even take they miraculously find that the one random knife they do take is the murder weapon. Incredible. Except of course it was bollocks. The knife had no blood on it. The positive for dna was so infinitismally small as to be conveniently too small for retesting and then we find the knife didn't even match the wounds. Which of course is why the forensic evidence around the knife is one of the key reasons the case was thrown out by the appeal court.