Contamination at the Laboratory
Of the three options for an innocent explanations contamination at the laboratory is the one that on the surface would appear to be the greatest concern. Laboratories follow strict procedures and do negative tests to insure against contamination but the sample on the knife was an LCN sample and we know that at least twenty items with Meredith's DNA had been tested in the laboratory before the knife. The argument that the reason Meredith's DNA ended up on the knife was because of laboratory contamination while improbable it might be a possible criticism from scientists such as Conti and Vecchiotti who are highly suspicious of LCN DNA.
Where the argument for laboratory contamination hits a dead end is with the testing schedule. No material related to Meredith's murder was tested in Stefanoni's laboratory for the six days prior to the knife. It is one thing to argue that the testing of the bra clasp just prior to the testing of the knife led to contamination but with a six day gap contamination is not possible. It is inconceivable that Meredith's DNA would survive multiple days of cleaning protocols. Further if a source of Meredith's DNA was present and acting as a contaminate then Meredith's profile should have appeared in the testing of materials completely unrelated to her murder. This would have been an immediate sign that something was wrong and the lab would have been able to address the issue.
Conti and Vecchiotti were appointed by Judge Hellmann to be impartial independent reviewers of the DNA evidence but quite quickly it became apparent that they were biased against the prosecution and there was even allegations and evidence indicating they were working with the defence but even Carla Vecchiotti confirmed that contamination at the laboratory was not possible.[5] if there was a six day gap in the testing of materials related to this case. It seemed painful to Vecchiotti but she said ruled out contamination and as such if an expert as hostile to the prosecution as Carla Vecchiotti ruled it out so can we -- Contamination at the laboratory is excluded as a possibility.
from
http://themurderofmeredithkercher.co...uble_DNA_Knife