secondary transfer of DNA to the genitalia
Suzanna Ryan
wrote, "An example of how secondary transfer could conceivably affect the interpretation of a case was illustrated by Sarah Jones and Kirsty Scott of the SPSA Forensic Services (Aberdeen) during the Body Fluids Conference jointly hosted by the Forensic Science Society & the Centre for Forensic Investigation, University of Teesside and reported in Science and Justice 50 (2010). Jones and Scott performed experiments to determine if non-intimate contact could result in the transfer of DNA to a male volunteer’s underwear and penis. Of three scenarios reported, one resulted in the transfer of the female volunteers’ DNA to both the underwear (33% of the samples) and penis (67% of the samples) of the male volunteers even though no direct contact from the female to the male had occurred. The scenario involved 1 minute of face-touching, 3 minutes of handholding and immediate urination by the male. However, when a 15 minute period was introduced between the non-intimate contact and urination, no female DNA was detected on either the underwear or penis of the male volunteers."
However, these sorts of scenarios do not explain Guede's DNA on Meredith's clothing or on her body. He did not have a date; he did not live at the house. That is one of several reasons to trust the DNA evidence against him more than against Ms. Knox. However (as I have said previously), we can toss 100% of the DNA evidence against him if we don't trust any of the DNA forensics, and he is still guilty BARD twice over. I would convict him on the bloody handprint alone.
EDT
It is extremely unlikely that Guede's DNA came to be where it was other than by intimate contact, the tampon conjecture to the contrary notwithstanding. Of course one obvious way to settle the matter is to test the putative semen stain twice, once to determine whether or not it is semen and once for DNA.
