Here were my questions (asked via email):
"1. Is DNA profiling not a confirmatory test for blood, and if so, why not? The only reason that I can think of is that one might detect DNA from any tissue.
2. If these tests (luminol, TMB, and DNA profiling) were the only tests done, what should one conclude about the luminol-positive footprints?"
Dr. Lednev indicated in his email that he and Kelly Virkler had discussed the matter and that this was a joint answer:
"-TMB can give a false negative if the blood is too aged or diluted, and other substances like acids or reduction compounds can interfere.
-On the other hand, Luminol can give a false positive with things such as bleach, Drano, and plant products. This would explain why there was no DNA found.
-Some luminol formulations can also damage DNA, so this might be a factor.
-So, there was either no blood and the luminol was wrong, or there was blood and the TMB had interference and the luminol damaged the DNA. We think it is more likely that there was no blood, and that the luminol was reacting with something else, possibly plant matter from the bottom of the shoes causing the footprints (the intensity of the luminol reaction might give some more insight). The prosecution should have used much more convincing evidence to prove the presence of blood.
It is correct to assume that DNA profiling is not a confirmatory test for blood because it can be found in so many other things. Just confirming the presence of the victim or suspect's DNA has absolutely no bearing on what type of tissue or fluid it is. There could have been skin cells scattered in a pile of ketchup that would match a person's DNA, but that doesn't make it blood. However, as outlined in our review (Forensic Sci. International 2009), there are several new mRNA based tests that CAN specify a body fluid based on certain markers, and some can even simultaneously compare DNA profiles."