from an earlier post...I forget which thread..sorry if it was this one.
Take the blood on the jacket for example. Some say it wasn't blood..if the dna was from something other than "blood"...it would have tested negative, see? The dna matched. The only way it could have tested a false positive is if it was from a potato or horseradish. That theory was negated by the fact that the DNA was there. SO...it wasn't spit, it wasn't snot, it was blood.
http://www.thesandiegochannel.com/sand/news/stories/news-152281920020620-130651.html
Three stains tested positive for the presumptive presence of blood, the criminalist testified. They were on the front right middle, the front right shoulder and the neck portion of the jacket, he said.
The Kastle-Meyer Color Test uses a solution of phenolphthalein and hydrogen peroxide on a piece of filter paper, and when blood of any quantity is present, it turns pink. However, it also turns pink in the presence of potatoes or horseradish, so care must be taken at the scene.
http://www.crimelibrary.com/forensics/serology/3.htm
It all makes sense, unless you allow for the possibility that a dna containing substance was wiped over the "Stain" by persons unknown. Why weren't the serology tests done?
Drool or spit can also cause the presuptive test to react. I know it's splitting hairs, but "Drool found on DW" does sound a little less ominous than "Blood found on DW"