Dan O.
Banned
- Joined
- Feb 14, 2007
- Messages
- 13,594
You misunderstand what i was trying to say, and I can understand it from the way I worded it. I worded it poorly.
So I will try and explain what I meant. If you have a positive result with luminol and you then test what the luminol reacted with using LCN testing. You will then know if its possible what it reacted to is blood. Not because LCN can tell the difference between blood, but because in this instance there was No DNA. As so many guilters go to great lengths to point out. You only need 1 cell of dna. If there is that much blood evidence using luminol how is there no DNA. Anything that would destroy evidence of dna would destroy the evidence of blood. If there is blood, there must be dna. Since there is no dna, its not blood. Thus the dna testing can prove its not blood, since there is no DNA. Red blood cells are not the only thing in blood. However, in the instance of the footprints, TMB and Dna tests where performed. TMB didn't react to any blood and the dna tests didn't find any dna. It talks in that very article about how luminol doesn't effect dna tests.
Yes, stated that way you ar correct. A negative DNA test would show that the substance the Luminal reacted to could not be human blood.
Conversly though, a positive result for DNA (especially at the LCN level) does not prove that the substance is blood because the DNA could be coming from another source such as shed skin cells that are expected to be found.
You are also quite right about the quantity verses concentration issue that seems to confuse many on the guilty side. Luminal is a catalytic reaction that requires a minimum concentration of the catalyst (iron as found in blood) to maintain a visible reaction. Whereas DNA tests separate the DNA from the sample and after PCR amplification give a reading that is relative to the number of segments of DNA that had been in the sample regardless of the concentration.