Frank seems to say Vinci found the stains over a year after the murder and that the defense deliberately did not test them.
"But it's a fact that the defense has been withholding some arguments and evidence for strategy reason. Useless to deny it by now since things are leaking: yes, on certain elements there has been a pact of silence.
But pacts are done to be broken (not by me) and today we can also talk about some important traces on the pillowcase found more than one year after the crime.
The stains should be tested to know if the substance is really sperm and who belongs it to. But nobody required that test and the evidence wasn't presented in court. Why was that?
Useless asking the defenses, the reserve is total about that.
But we can understand that a contamination may have easily occurred, and if the test resulted a DNA belonging to Raffaele that would be a serious problem. Better not to take the risk, they must have thought (for not to mention that the defenses, for technical reason, maintain that there wasn't sexual violence).
So, it looks like the piece of evidence will not enter this trial since both defense and prosecution seem to be paralyzed by the risk that the test may result something inconvenient for them.
In conclusion, for a number of reasons, we don't know yet if that substance is really semen. It could, for instance, be vaseline, which doesn't have DNA and could go undetected with the swabs."
http://perugia-shock.blogspot.com/2009/10/defensive-strategy-for-knox-and.html