This simply isn't true. False positives in fact ARE COMMON.
There are countless substances that react to Luminol. Luminol reacts to any substance that contains copper, iron, cyanides, bleaches as well as specific proteins.
Fecal matter does not react to luminol or TMB, unless it contains blood (it should not); as well as urine should not react, if it does you should seek treatment.
Bleaches instead is another issue (note: it has the power to react to TMB as well).
Well bleach, first, it reacts in a way that forensics are supposedly trained to distinguish it from blood. Light emitted is not at the same wavelength, has a slightly higher pitch, but above all the timing of reaction is different. The glow of blood and enzymes would fizzle down slower, they will keep a peak after 20 seconds and will retain some visible luminescence for about two minutes, while the peak of chlorine is more intense and disappears more quickly, in less than half the time.
However the most important thing, is that chlorine is found by literature to be volatile. The stain it loses the property of reacting to luminol within a very short time. The property to react to luminol disappears in fact after only a few hours. Sodium hypochlorite does not precipitate, it evaporates with the water solution as the stain dries out; Creamer and Quickenden point out that despite stabilizer, after 8 hours the common house bleaches would show no longer any reaction to luminol.
Moreover, bleach destroys DNA, while DNA was found in many latent traces.
Finally, just bear in mind that bleach is not supposed to come into contact with human skin; there is no reason why someone should steep their feet or walk in a bleach dilution.
Now, if the topic of contention was about the alleged power of TMB as
a falsifyer, then when you mention salts of copper, iron and other compounds of non-human use, then you need to consider that – so literature shows –
TMB also reacts with such compounds. TMB reacts to iron, copper, nickel; it also reacts to enzymes containing a heme or to some chlorophylls.
If you assume there was, let’s say, a nickel of copper based soil diluted in water, well, besides the fact that the presence of such oxides as “common” in that house or in that environment should be shown, since there would be clues of that presence all over the house, not just in isolated prints, anyway if the presence of that substance was significant, the stain would anyway react to TMB.
Contrarily to the claims of others, a lack of reaction to TMB coupled with a positive luminol reaction does not mean “something else” different than blood, but it means low dilution (of whatever substance that is).
Why do forensics manuals instruct techs to perform BOTH TESTS?
Why do forensic manuals instruct techs to perform a confirmatory test?
The answer to the second question is obvious, since luminol and TMB are presumptive tests while human-antibodies test indicates human cells unambiguously, it is logical that you would attempt to get full information from a specific confirmatory test. Unfortunately, the specific anti-body test for blood does not have remotely the sensitiveness of presumptive tests like luminol or TMB, thus may be negative on stains that are latent, diluted or washed away. It is logical for it to be recommended, but it is not logical to expect it to be always positive.
As for the first question, after saying I actually don’t know these alleged instructions on manuals, which you don’t quote, anyway, I say that if some manuals say that, I don’t know why they do.
There may be good reasons to always run a TMB test, since it is very easy and cheap to carry out, and luminol may not always be an immediate or safe response (think about that you are in the dark meaning extreme conditions where you can’t film document or take pictures and you have later to retain and develop or print a photography, etc.). And I think TMB is also the default and first test to carry on since it is what you do when you see the visible traces. I think any ‘protocol’ may be developed from the procedure used for visible stains, and may be aimed at minimizing risks of mistakes.
But these speculations are not really important. What I know is that ‘protocols’ are not evidence that some procedure is actually logical, useful, proper or scientific. It is just unscientific to assume so. It is a frequent error to mistake established technical procedures with science, or as evidence that the procedure is the best one. Angelina Jolie decided to undergo a double mastectomy while she was healthy and had no breast cancer, since doctors found a gene which put her at high risk. There was a medical assessment behind this decision, a procedure believed to be a scientific approach by some American physicians. Most European doctors viewed the decision to remove the target-organ as wrong and inappropriate. Opposite opinions, divergent protocols, technical assessments and ‘schools’ co-exist.
And it also happens that scientific communities changed their opinions on techniques that were believed to be scientific and established, that were later abandoned and as knowledge developed they were later deemed unscientific, or anyway no longer the best choice.
Electro-shock was considered a scientific treatment in psychiatry for almost eighty years; after that, in the recent decades, it happened to be proven to be absolute crap. But it was ‘science’ for eighty years. There have also been seventy or so years of lobotomy. For the cure of tuberculosis, doctors believed that artificially provoked pneumothorax could be helpful to allow the lung to rest and thus diminish inflammation, exhaustion and help the patient to breath. This technique was believed to be scientific for over fifty years, until the seventies. Then it was found to be totally unscientific. For the cure of epilepsy, for decades doctors would employ a treatment based on insulin aimed at causing ‘insulin-shock’ and hypoglycemic coma, which was believed to be effective to cure acute episodes. This also was proven unscientific only after decades. Why did the previous protocols say that? I don’t know. What I know is that protocols contain errors, but the recommendation of performing a TMB test is totally harmless, whether right or wrong.
Assessments about techniques and best approaches also change: until about ten years ago, surgery was considered the best approach to most discal hernias; today, discal hernia surgery is considered a useless technique for most cases. Knowledge and techniques have changed and consequently assessments and recommendations.
I don’t know if performing a TMB test on a luminol positive latent stain is right or wrong, it it’s sometimes useful or never useful, if it’s logical or not. What I know is that it’s easy cheap and harmless, so even while I doubt its utility I would keep the recommendation.
Why did Stefanoni perform a TMB test if she plans to ignore a negative result?
The question is related to the previous points: Stefanoni simply follows a praxis, or a ‘protocol’. This does not mean that the protocol is necessarily rational or scientific; also, it doesn’t mean that Stefanoni has a ‘plan’ to ignore it. But why should I rule out that she may later decide to ignore it, if there is logical basis to do so?
Why can't you see these prints with the naked eye?
If they were cleaned by Amanda and Raffaele after the crime, why aren't they "streaked"?
The questions aim at considering whether the stains were cleaned up or not.
There are two possibilities, I don’t know if the stains were invisible since their origin, or whether there has been a cleaning with a mop.
On the small bathroom floor, and in front of Meredith’s door, I am positive that the floor was cleaned. While instead in Amanda’s room and in the other spots in the corridor I don’t now.
If the luminol prints they were cleaned up when they were already dry, I don’t see why the latent traces should be “streaked”; however, for two of the prints in the corridor, I do notice there are some very visible “streaks” all around the prints area, looking like signs of sweeping the floor exactly in the area of corridor where the two prints are located.
