FACT: Defense attorneys for both Amanda and Raffaele have formally petitioned the court to have this testing donei, and the request has been denied. This is a major element of Raffaele's appeal, and defense lawyers are continuing to hope they can get this test done.
A basic, generic understanding of criminal investigations helps here. The police confiscate and log evidence from the crime scene. A discovery process ensures that the defense can learn about and examine this evidence. BUT, if they want to subject evidence to a chemical test that will be destructive, i.e., will change or "use up" the evidence or a portion thereof, they can't just do it on their own initiative, for reasons that should be obvious. Instead, they have to petition the court and explain what they want to do and why. This is what defense attorneys have done in the case of the possible semen stain on the pillow.
As for the technology used to detect the stain, it was a crimescope, which is a specialized tool that can cast light in a number of very precise color bands. Different bands reveal different kinds of stains. This is what Vinci used in his analysis and how he discovered the possible semen stain. If you view his presentation, available at:
http://www.friendsofamanda.org/vinci.pdf
you will see a picture of the crimescope.e The police investigators in this case had and made use of a crimescope. It can be seen in some of the crime scene video.
As for the stain, everyone recognizes that it might not be semen, and if it is semen, it might be from to Meredith's boyfriend. But it's also quite possible that it is Guede's. It is important to test it because it may add to the court's understanding of what happened that night.
