The Double DNA Knife
Meredith Kercher had never been to Raffaele Sollecito's apartment so there are only three innocent ways to explain the presence of her DNA on the blade of the knife.
Contamination During Collection
The issue of contamination is fairly easy to address. There are two ways that contamination could have happened - contamination at collection or contamination at the laboratory. The forensic team that searched Raffaele's apartment had no personnel in common with the forensic team that searched the cottage. This makes contamination during collection impossible.
Contamination at the Laboratory
Contamination at the laboratory would have been more of a concern except that no material related to Meredith murder was tested in Stefanoni's laboratory for the six days prior. Confronted with this fact that the lab had Carla Vecchiotti confirmed that contamination at the laboratory was not possible.
Secondary transfer is the process when someone transfers someone else's DNA. An argument for secondary transfer is difficult to accept. Meredith's DNA was not discovered anywhere else in Raffaele's apartment. That the only instance of secondary transfer would involve the blade of a knife is astronomically unlikely.
- Staff. [http://www.repubblica.it/cronaca/2011/07/30/news/meredith_processo-nuovo-19812721/ "Meredith, periti Dna in aula Il coltello non fu lavato"] la Repubblica 30 July 2011