DNA isn't that easy to remove. That's one of the reasons the Meredith DNA isn't reliable. That being the contamination factor in the lab. They don't wash down the machines with soap and water but rather a strong bleach solution or other special solutions
UltraClean® Lab Cleaner efficiently removes nucleases (DNase and RNase) and nucleic acid (DNA and RNA) contamination from pipets, bench tops, glassware and labware by simply wiping and rinsing. UltraClean® Lab Cleaner replaces time-consuming processes such as DEPC treatment and autoclaving and is useful for RNA, DNA, and PCR experiments.
What is more remarkable is as Tesla described. The ONLY reason that the knife was ever considered the murder weapon was the DNA of Meredith Stefanoni "found" on it.
The PGP can't seem to get that at all.
It has been repeated here a number of times and I have no information to the contrary but is it really true they only tested 3 knives?
It is beyond mind-boggling that they wouldn't have tested many more knives especially the ones that fit the outline and the wounds. Hey, maybe one that had a hilt that could have left the bruise.