Thanks for that. I'm puzzled though, didn't some of the actual blood stains (e.g. the marks on the wall) test negative with the TMB test? Just going from memory so I'd need to check it. If visible stains can test negative with TMB, then I wouldn't think it would be surprising that very diluted and invisible traces might also test negative. As I said though, I'd need to check on that one.
I suspect you're thinking about the one on the pillow, and reason it might have have been visible and tested negative for blood might be because it wasn't actually blood. It could have been fake blood from her Halloween costume she didn't completely remove when she got home early that morning.
The odds of a false
negative are in fact pretty low, which is why there's not a whole lot of literature about them. After all, it's not a confirmatory test for human blood anyway, even with a positive it has to go back to the lab. They use them because they're simple and can be done on-site and will generally
eliminate the possibility of blood, if they didn't do that there would simply be no point to using them. However it was necessary to come up with something because they had to explain the negative TMB results after they were accidentally discovered. The thing is though, what they came up with doesn't work either, as the case in Massei relies upon the dilution to explain the negative TMB test:
Massei PMF page 282-283 said:
But it must be noted that the negative result for blood does not necessarily indicate that no blood was present. The result may have been negative because there was not sufficient material to indicate the presence of blood. Dr. Gino stated that in her experience there is a probabilistic relation to the number of cases in which the blood test comes out positive or negative. The negative result was also partly a consequence of Dr. Stefanoni's choice to use most of the DNA to determine the individual profiles and only the remainder to attempt to determine the nature of the trace. Furthermore, since the traces revealed by Luminol ?? it becomes certain that the traces contained human DNA. The fluorescence ?? implies that the biological material (in which appears ?? human) was Luminol-positive.
Corruption (??) inherent to to the original. The point is Massei's case is disproven by the fact a negative TMB test due to dilution (which would also be the case if there 'wasn't enough left') isn't going to give off that bright glow.
I recall someone (might've been halides) saying that bleach evaporates quickly, so it seems unlikely they could've been made in a bleach-containing cleaner at any rate.
Simple bleach will at first completely interfere with the test as it is impossible to determine by simply eye-balling it whether it's blood or bleach. It's all bright blue. However given time (46 days is plenty) simple bleach will fade and just kinda looks milky. However that's
hardly the only bathroom cleaner that can give off a luminol hit, and even standing bleach (like what might pool at the bottom of a shower) can have something happen to it which causes it not to fade.
The fact that the bleach effect fades isn't really relevant as that just means it's not simple bleach, it hardly eliminates all bleach containing cleaners as they might contain other chemicals that cause a similar effect and
don't fade. There were just some bunnies and kittens who thought bringing up that paper that who tried to contend that eliminated
all possibilities of bathroom cleaners solely because in that one instance it would have faded in 46 days. Did I mention bleach? That was just a brain-fart if I did.
But certainly the luminol hits at Raffaele's place tend to suggest getting a positive luminol reaction isn't that uncommon and that it definitely isn't specific to blood.
As I recall most were found in or around the bathroom too, suggesting even more so that bathroom cleaners that
aren't simple bleach give off luminol hits.
I think I need to read some more on this one. I've heard the arguments on the prints not being made in blood, based on the negative TMB test and the intensity of the light from the footprints (most likely increased by misapplication of the luminol, though) and they seem quite convincing. But how does that fit with visible blood stains testing negative with TMB?
I am unfamiliar with how the over-application of luminol might have caused highly diluted stains to glow brighter, that doesn't make sense to me. The chemiluminescence is caused (in the case of blood) by the reagent catalyzing with the hemoglobin. The more diluted, the less hemoglobin no matter how much luminol is applied. Perhaps you are thinking of the excuse for why (most of) the footprints tested negative for DNA? That was due to claiming an over application of luminol destroyed the possibility of DNA testing. Meaning they wanted to get those pretty pictures and they kept applying the luminol to keep the glow going while they got the camera set up, each time removing DNA in the process, thus we're supposed to assume they might have recovered DNA had they not been so stupid about it? Personally I think that's an absolutely bizarre argument for them to make: 'give us a break, if we weren't such incompetent clowns we might have found DNA so you have to assume we did!'
At any rate, it doesn't really matter.
Even if they had positive TMB and DNA tests, they didn't
prove blood:
NFSTC said:
Confirmatory tests are then used to identify the specific biological material, which can then be typed.
The line between screening and identification is not always clear. For example, while examining the clothing of a suspect, a forensic biologist might visually locate a brown stain that presumptively tested positive for blood and was then DNA typed. The DNA type is found to match the victim. Knowing that the loci tested are higher primate specific, what conclusions can be drawn?
The only unqualified conclusion that can be offered is that the stain contains DNA that matches the victim. It has not been proven to be blood.
If asked “Could the results have arisen because the material tested was the blood of the victim?” then an answer of “Yes” is justified. However, it would be wrong to report that the material was human blood with a DNA type that matched the victim. The material was not subjected to confirmatory testing for blood or proven to be human in origin.
It's just a sad, pathetic excuse by Stefanoni, an attempt to baffle the court with BS as who'd believe she'd try to deceive them? Comodi can just say 'They could be turnip juice or blood, you decide.' The defense has to go through all this and puts the jury to sleep, think about it: who's still actually reading at this point? We put everyone else asleep long ago, as one must have the endurance of an elephant to wade through too much nonsense about luminol, TMB and confirmatory tests!
