I was watching a tv show The Killing Fields Killing Fields Season 1 and watched the police spray luminol on an area of the floor and almost immediately the area showed blue. They also noted that there was a professional mop and bucket near by, that indicated the floor may have been cleaned. After the sample was sent to the lab, it came back that it was not blood, and the lab was not sure what it was. I was perplexed by that as I thought that luminol showed blue when there was blood. I began to do some research and wanted to show my findings to everyone and maybe clear up misconceptions about luminol.
An article, which by the way is very informative about this subject and brings up several notable past murder cases, entitled, Professional Opinion from Veteran FBI Agent Steve Moore listed the following:
“1. A mixture of luminol powder and hydrogen peroxide is mixed in a spray bottle like you buy at the grocery store.
2. The mixture is sprayed on areas where blood (or other substances) are expected to be.
3. The mixture reacts to many things, but one of them is the iron in hemoglobin (a component of blood) which causes the mixture to glow. The luminol, like the light stick, has a limited fluorescent life. In the forensics application, the glow lasts about 30 seconds.
4. On those areas where you get a “hit”, you photograph quickly, and then test the site for indicators of what the “hit” was. You first test for the presence of blood, then if not blood; other substances. If it is blood, you can then conduct a DNA test. (Luminol does not disrupt blood or DNA testing).
5. Importantly, you take a control sample from a nearby area that did NOT fluoresce, so you can be certain that your tests are valid.
6. There is no difference in the fluorescent color of luminol, no matter what substance it is reacting with. If it reacts with blood, it is blue. If it reacts with bleach, it is the same color of blue.”
Where I always believed that the ONLY thing that showed up when you spray luminol was blood. I now understand was false. Luminol will also light up poop and horseradish and bleach, the one thing that is commonly used to clean up blood. It is also used by scientist to detect copper, iron, and cyanides
You don’t know if the blue reaction is blood or bleach or even horseradish, until you take it to the lab for testing, where they will see if there is hemoglobin. This also explains why the lab stated why they didn’t know what it was that was found on the kitchen floor, because blood is not the only thing that will react to luminol. In this case, because they were in the kitchen, if the person was a horseradish enthusiast and put horseradish on everything and dropped some on the floor, or even if the dog gone dog pooped there, when the luminol was sprayed, the floor would shine blue.
Then you also have the issue of blood other than human. According to National Center for Biotechnology Information, “It was found that bovine haemoglobin and human haemoglobin showed no significant spectral differences.” Holy cow, so if you drop a steak on the floor and clean it up with bleach, the hemoglobin will be found, but whether it is human or the steak could be argued, especially if it is found in a kitchen.
I also found that there are different types of bleach that react differently to luminol. According to Explore Forensics, chlorine bleach can remove the stain, but luminol can still detect it. But bleach that has an oxidizing agent, like hydrogen peroxide, can completely remove the blood and the luminol cannot detect it.
Then you also have to look at where the blue light is reacting. For example, if the reaction is on the floor, anything could have been dropped there, but if it is on the wall and on the ceiling, it is very unlikely that someone was cleaning the ceiling, or if they were they were cleaning blood. That is why police will go to the extreme of taking off trim and looking in cracks, and checking for blood splatter for an area that might not have been cleaned by bleach. They are looking for hemoglobin.
With all this information you can see why police are very stoic about talking about evidence, especially when it comes to blood. There are so many variables that, although it seems to you and I, a clear case of who done it, it is actually difficult to prove in court and is just another tool used to prove a case.
You might also like to read: Can Paint cover up human blood?
TaoTronics TT-FL001 UV Flashlight Blacklight, Dog Urine and Stains Detector, 12 Ultraviolet LED Light with AAA Batteries UV Light is another tool that is used and you can read more here.