When Comodi cross-examined Vecchiotti, Vecchiotti said that a six-day gap in testing should be sufficient [presumably to exclude in-lab contamination] if that is the way things went (I am basing this on how the exchange was reported in Follain's book). There are some ifs, ands, and buts that need to be stated IMO.
One is that gaps in the testing have nothing to do with contamination outside of the laboratory. That is worth keeping in mind with respect to the bra clasp, where contamination outside of the lab is so likely. I have examined the egram of the Y chromosomal profiling. There are between 2 to 4 additional male contributors to the DNA besides Raffaele. We are all agreed that four other men did not take part in the crime; therefore, the bra clasp is contaminated by definition. DNA forensic scientist
Van Oorshot wrote, "any DNA deposit that is not immediately relevant to the crime being investigated can be viewed as contamination. In this light, gross or sporadic contamination may appear at any point: (1) before the crime has been committed; (2) in the interval between the crime and securing the crime scene; (3) during the investigation of the scene; and/or (4) within the laboratory."
Two, the six-day gap argument is
problematic on multiple grounds, especially with respect to the knife profile (I discussed this extensively elsewhere). There is a one-day gap in the contamination that occurred in the Farah Jama case, and there is a two-day gap that occurred in the Jaidyn Leskie case. If a one-day and a two-day gap are demonstrably insufficient to rule out contamination, what is so special about a six-day gap?
Three, the claim looks even more suspect when one realizes that DNA can persist on laboratory tools for at least three months, as a 2006
study by Poy and Van Oorshot showed. These authors also noted, "To further help evaluate the above finding swabs were taken from gloves worn whilst examining a heavily soiled dress during routine casework examination. A significant amount of DNA was retrieved which exhibited a genetic profile that matched that of samples taken from the exhibit."
I am now returning to lurker status, but may occasionally be available through PMs.