Discussion Document on Blood & DNA Removal
Is it possible to remove blood and DNA to an untraceable degree from a blood-stained ornamental hammer?
Thomas Mollett – October 2020
Disclaimer: This is not an academic article, but merely a discussion document – albeit with a conclusion rendered. Hence, it mainly consists of verbatim extracts from literature sources, put in inverted commas. Where “[. . .]” is indicated, it shows that an irrelevant part has been removed for the purpose of brevity, but, while in no recognised style, reference is made to the original source. All underscoring, italics, and bolding were added by the author of this discussion document.
Assuming, for the purpose of the discussion, and on the premise that the hammer shown below has been used in an attack on a victim by multiple blows on the victims head, the question that this discussion document serves to explore is whether it is possible to clean such an object with cleaning agents to the extent that:
- Luminol, as a presumptive test, will either show an inconclusive reaction and/or no reaction at all, after being treated with Luminol specifically; and
- Whether it is possible to remove all of the victim’s DNA from the object – not only to be unable to yield full profiles, but that physically no DNA of the victim can be found on such an object after a cleansing process.
1. What is Luminol?
1.1 “Luminol is frequently used as a searching or enhancement method at the crime scene. The test is based on the ability of the luminol molecule to be oxidized by the reaction of sodium perborate with an oxidizing agent such as hemoglobin (or other strong oxidizers such as iron, bleach, cleaning agents, and some foodstuffs).” – Marilyn T. Miller, Ed. 2018. In Crime Scene Investigation Laboratory Manual (Second Edition). Source
1.2 “The body requires iron for the synthesis of its oxygen transport proteins, in particular hemoglobin and myoglobin, and for the formation of heme enzymes and other iron-containing enzymes involved in electron transfer and oxidation-reductions. Almost two-thirds of the body iron is found in the hemoglobin present in circulating erythrocytes [red blood cells], 25% is contained in a readily mobilizable iron store, and the remaining 15% is bound to myoglobin in muscle tissue and in a variety of enzymes involved in the oxidative metabolism and many other cell functions.” – N. Abbaspour et al., 2014. ‘Review on iron and its importance for human health’. Source
1.3 “Luminol solution reacts with blood to produce light. The luminol solution contains both luminol (C8H7N3O2) and hydrogen peroxide (H2O2). The hydrogen peroxide reacts with the iron in blood to produce oxygen. This oxygen then reacts with the luminol, changing the structure of the molecule and temporarily adding energy. When energy is added to molecules, it is often absorbed by electrons (tiny charged particles). By absorbing the energy and becoming “excited,” the electrons move to a higher energy level. Then, when the electrons return to their natural, “unexcited” level, they release the energy as visible light.” – Oregon Museum of Science and Industry, 2007. Source
1.4. “Hemoglobin is the protein inside red blood cells. It carries oxygen. Red blood cells also remove carbon dioxide from your body, transporting it to the lungs for you to exhale.” – University of Rochester Medical Centre, 2020. ‘What are red blood cells?’ Source
2. Why Luminol reacts with Blood
2.1 “Iron is an essential element for blood production. About 70 percent of your body’s iron is found in the red blood cells of your blood called hemoglobin and in muscle cells called myoglobin. Hemoglobin is essential for transferring oxygen in your blood from the lungs to the tissues. Myoglobin, in muscle cells, accepts, stores, transports, and releases oxygen.” – UCFS Health, 2020. ‘Hemoglobin and function of Iron’. Source
2.2 “The body requires iron for the synthesis of its oxygen transport proteins, in particular hemoglobin and myoglobin, and for the formation of heme enzymes and other iron-containing enzymes involved in electron transfer and oxidation-reductions. Almost two-thirds of the body iron is found in the hemoglobin present in circulating erythrocytes [red blood cells], 25% is contained in a readily mobilizable iron store, and the remaining 15% is bound to myoglobin in muscle tissue and in a variety of enzymes involved in the oxidative metabolism and many other cell functions.” – N. Abbaspour et al., 2014. ‘Review on iron and its importance for human health’. Source
2.3 “Luminol solution reacts with blood to produce light. The luminol solution contains both luminol (C8H7N3O2) and hydrogen peroxide (H2O2). The hydrogen peroxide reacts with the iron in blood to produce oxygen. This oxygen then reacts with the luminol, changing the structure of the molecule and temporarily adding energy. When energy is added to molecules, it is often absorbed by electrons (tiny charged particles). By absorbing the energy and becoming “excited,” the electrons move to a higher energy level. Then, when the electrons return to their natural, “unexcited” level, they release the energy as visible light.” – Oregon Museum of Science and Industry, 2007. Source
2.4. “Hemoglobin is the protein inside red blood cells. It carries oxygen. Red blood cells also remove carbon dioxide from your body, transporting it to the lungs for you to exhale.” – University of Rochester Medical Centre, 2020. ‘What are red blood cells?’ Source
[Note: The Luminol solution reacts with the iron in haemoglobin in red blood cells, by emitting light after the oxidation process excites the H2O2 component of it. Haemoglobin is located inside the red blood cell.
3. Constitution of Blood & DNA Content
3.1 “Blood is a specialized body fluid. It has four main components: plasma, red blood cells, white blood cells, and platelets. [. . .] White blood cells [leukocytes] protect the body from infection. They are much fewer in number than red blood cells, accounting for about 1 percent of your blood.” – American Society of Hematology, 2020. Source
3.2 “[. . .] white blood cells account for only about 1% of your blood [. . .]”– University of Rochester. 2020. Source
[Note: White blood cells contain: Neutrophils, Lymphocytes, Monocytes, Eosinophils, Basophils]
3.3 “Unlike the rest of the cells in your body, your red blood cells lack nuclei. That quirk dates back to the time when mammals began to evolve. Other vertebrates such as fish, reptiles, and birds, have red cells that contain nuclei that are inactive. Losing the nucleus enables the red blood cell to contain more oxygen-carrying hemoglobin, thus enabling more oxygen to be transported in the blood and boosting our metabolism. This is the first study to reveal the proteins involved as a red blood cell loses its nucleus. The researchers plan to further investigate the entire process of red blood cell formation, which may lead to insights about genetic alterations that underlie certain red blood cell disorders.” – Whitehead Institute for Biomedical Research, 2008. Source
3.4 “Platelets are irregularly shaped, have no nucleus, and typically measure only 2–3 micrometers in diameter. Platelets are not true cells, but are instead classified as cell fragments produced by megakaryocytes. Because they lack a nucleus, they do not contain nuclear DNA.” – Nature, 2020. Source
3.5 “Thus, platelets resemble cell fragments rather than fully licensed cells. One of the strongest arguments is probably that platelets have no genes to reorganize, because they have no nucleus and supporting DNA material (apart from the mitochondrial genome).” – Frontiers in Immunology, 2015. ‘Are Platelets Cells? And if Yes, are They Immune Cells?’ Source
3.6 “Plasma is the largest part of your blood. It makes up more than half (about 55%) of its overall content. When separated from the rest of the blood, plasma is a light yellow liquid. Plasma carries water, salts and enzymes.” – University of Rochester, 2020. Source
3.7 “Nuclear DNA is only found in nucleated cells – this rules out three of the four major components of blood: red blood cells (which don’t have nuclei), platelets and plasma. So you only get nuclear DNA in white blood cells, which are outnumbered by red blood cells in the blood stream by about 600 to one.” – ABC Science, 2019. Source
Author’s Note: As confirmed by the above-mentioned sources, in blood, only white blood cells contain a nucleus with DNA within the cell’s nucleus. Neither red blood cells, platelets or plasma contain nuclei and therefore no DNA. White blood cells constitute only about 1% of blood’s constitution. Compared to red blood cells there are about 600 red blood cells for every one white blood cell.
4. The Removal of Blood from Various Objects
4.1 “A team of scientists from the University of Valencia (UV) has proven that traces of blood in various materials are eliminated completely when they are washed with detergents containing active oxygen. The conclusion of the study, published in the latest number of the German journal entitled Naturwissenschaften, points out that these new products alter blood to such an extent that this cannot be detected by reagents used in forensics.” – Science Daily. 2009.
Read the full article here
And read the full original article by Castelló et al., 2009 – ‘Active oxygen doctors the evidence’ in Naturwissenschaften here
Which concludes with: “The results show that regardless of the type of blood used to generate stains, the age or backing on which they were placed (soft cotton cloth, jeans fabric, toweling) or the washing conditions employed (hot or cold water), washing fabric with products containing active oxygen prevents positive results from being found using presumptive and human haemoglobin tests.”
Author’s Note: A subsequent study by the same authors found that treatment (cloth material at least) with active oxygen agents does not necessarily mean a DNA profile cannot be obtained. While the studies were not compared in detail by the author of this discussion document, it is worrying that the authors of the article state: “These findings [of their previous study] have caused considerable concern both within the forensic and scientific community, and among the general public, so obliging us to seek solutions.” (This will be addressed further in the Post Scriptum of this document.) Source
Author’s Note: Vanish O2 entered the South African market in 2003 – it contains sodium carbonate peroxyhydrate that dissolves in water to form hydrogen peroxide and sodium carbonate – both powerful cleaning agents.
4.2 “Chlorine bleaches can remove a bloodstain to the naked eye but fortunately, forensics experts can use the application of substances such as luminol or phenolphthalein to show that haemoglobin is present. In fact, even if the shady criminal washed a bloodstained item of clothing 10 times, these chemicals could still reveal blood. [. . .] With oxygen bleach, the bleach has an oxidising agent, which could be a substance such as hydrogen peroxide. In these instances, haemoglobin is completely removed and can’t later be detected. As expected, this presents a unique challenge for forensic scientists. Not only that, but it can significantly compromise an investigation and may mean that evidence is not properly investigated and used in a trial.”– Explore Forensics, 2016. Source
4.3 “The forensic luminol test has long been valued for its ability to detect trace amounts of blood that are invisible to the naked eye. This is the first quantitative study to determine the effect on the luminol test when an attempt is made to clean bloodstained tiles with a known interfering catalyst (bleach). Tiles covered with either wet or dry blood were tested, and either water or sodium hypochlorite solution (bleach) was used to clean the tiles. As expected, the chemiluminescence intensity produced when luminol was applied generally decreased with the number of times that a tile was cleaned with water, until the chemiluminescence was neither visible nor detectable. However, when the tiles were cleaned with bleach there was an initial drop in chemiluminescence intensity, followed by a rise to a consistently high value, visibly indistinguishable from that of blood. Examination of bleach drying time suggested that any interfering effect becomes negligible after 8h.” – J. Craemer et al., 2005. ‘Attempted cleaning of bloodstains and its effect on the forensic luminol test’. Luminescence: The Journal of Biological and Chemical Luminescence. PubMed. Source
4.4 “Blood at crime scenes is one of the most significant traces of evidence in investigation proceedings. Cleaning up these traces with household cleaning products, often containing bleaching agents, inhibits or complicates the detection of DNA. In this study, human blood was applied onto different floor coverings (carpet, laminate, parquet, PVC, tile) and subsequently cleaned with water and bleaching agents (hydrogen peroxide, sodium hypochlorite, DanKlorix®, Vanish Oxi Action®) at different times. Samples have been collected afterwards from the floors. The samples underwent a quantitative and qualitative DNA analysis. Cleaning smooth surfaces with water is usually sufficient to prohibit retrieving a DNA profile in most of these cases. Cleaning carpets were more difficult due to their absorbent surface whereas the use of bleaching agents caused an additional reduction of verifiable DNA concentrations. Retrieving partial or complete profiles after the use of bleaching agents was only possible when cleaning with low concentrations of 3% hydrogen peroxide.” – Edler et al., 2020. ‘The effect of bleaching agents on the DNA analysis of bloodstains on different floor coverings’. ResearchGate. Source
5. DNA and Cells
5.1 “In organisms called eukaryotes [an organism consisting of a cell or cells in which the genetic material is DNA in the form of chromosomes contained within a distinct nucleus], DNA is found inside a special area of the cell called the nucleus. Because the cell is very small, and because organisms have many DNA molecules per cell, each DNA molecule must be tightly packaged. This packaged form of the DNA is called a chromosome.” – National Genome Research Institute, 2020. Source
5.2 “In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes. Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure.” – MedlinePlus, 2020. Source
5.3 “Chromosomal DNA is packaged inside microscopic nuclei with the help of histones. These are positively-charged proteins that strongly adhere to negatively-charged DNA and form complexes called nucleosomes. Each nuclesome is composed of DNA wound 1.65 times around eight histone proteins. Nucleosomes fold up to form a 30-nanometer chromatin fiber, which forms loops averaging 300 nanometers in length. The 300 nm fibers are compressed and folded to produce a 250 nm-wide fiber, which is tightly coiled into the chromatid of a chromosome.” – Scitable, 2014. Source & Read more about the DNA Packaging in the cell here
5.4 “A cell’s plasma membrane defines the cell, outlines its borders, and determines the nature of its interaction with its environment. Cells exclude some substances, take in others, and excrete still others, all in controlled quantities. The plasma membrane must be very flexible to allow certain cells, such as red and white blood cells, to change shape as they pass through narrow capillaries. These are the more obvious plasma membrane functions. In addition, the plasma membrane’s surface carries markers that allow cells to recognize one another, which is vital for tissue and organ formation during early development, and which later plays a role in the immune response’s “self” versus “non-self” distinction.” [. . .]
[. . .] A plasma membrane’s principal components are lipids (phospholipids and cholesterol), proteins, and carbohydrates attached to some of the lipids and proteins. A phospholipid is a molecule consisting of glycerol, two fatty acids, and a phosphate-linked head group. Cholesterol, another lipid comprised of four fused carbon rings, is situated alongside the phospholipids in the membrane’s core. The protein, lipid, and carbohydrate proportions in the plasma membrane vary with cell type, but for a typical human cell, protein accounts for about 50 percent of the composition by mass, lipids (of all types) account for about 40 percent, and carbohydrates comprise the remaining 10 percent. However, protein and lipid concentration varies with different cell membranes.” – Lumen, 2020. Source
6. Extraction of DNA from Cells
6.1 With regards to the extraction of DNA: “The cells in a sample are separated from each other, often by a physical means such as grinding or vortexing, and put into a solution containing salt. The positively charged sodium ions in the salt help protect the negatively charged phosphate groups that run along the backbone of the DNA. A detergent is then added. The detergent breaks down the lipids in the cell membrane and nuclei. DNA is released as these membranes are disrupted.” – Science Learning Hub, 2020. Source
6.2 “Detergent contains sodium laurel sulfate, which cleans dishes by removing fats and proteins. It acts the same way in the DNA extraction protocol, pulling apart the lipids and proteins that make up the membranes surrounding the cell and nucleus. Once these membranes are broken apart, the DNA is released from the cell.” – ResearchGate, 2017. Source
6.3 “[. . .] In this activity, students add soap to lyse (break open) the cell and nuclear membranes and release the DNA. Soap dissolves these membranes because they are basically layers of oil that surround the cell. In other words, dish soap destroys cell membranes in the same way that it cleans oil off dishes and pans. Cell membranes and oil are both made of molecules called lipids. Lipids are large molecules that have two parts: a small, compact hydrophilic head and a long, dangling hydrophobic tail. (Hydrophilic means attracted to water, and hydrophobic means repelled by water.) In lipids, most of the molecule (the tail) is repelled by water, while the tiny head is attracted to water. This head and tail structure of lipids allow them to arrange as large, two-layer sheets when they are in water. The sheet structure allows the hydrophilic, water-loving heads to be exposed to the water, while the hydrophobic, water-hating tails can be tucked into the interior of the sheet. The cell and nuclear membranes are such sheets of lipids, each with the water-attracting heads on the outside and the water-repellent tails on the inside.” – OMSI, 2007. Source
6.4 “Now think about when you wash your dishes– what does the soap do to the oil on the dishes? It breaks it up. Cell membranes are also made of lipids. By adding soap to your cheek cells, it breaks up the membranes of the cell and nucleus and frees the contents of the cell, including DNA. So the DNA begins to float near the top of the soapy water. DNA is soluble in water but not in alcohol. The alcohol helps the DNA precipitate or separate as a solid from a liquid solution. The result is a white clump of thousands of DNA strands that you can see with your naked eye.” Museum of Science and Industry, Chicago, 2020. ‘See your own DNA’. Source
6.5 Read more about Lysis (the disintegration of a cell by rupture of the cell wall or membrane) and detergents here
7. Bleach vs Blood
7.1 “Besides washing a bloodstained area with just soap and water, the use of bleach may also be used. To the criminal, this may represent a double benefit. It helps to clean up the bloodstain, and it is hoped the use of bleach also prevents subsequent DNA analysis of the blood. So, how does bleach react with luminol? Fig. 7.49 [below as Fig. 2] shows that bleach will fluoresce much more brightly than blood. The bleach will seem to “sparkle” at times. Blood usually fluoresces a dull blue. You may see a combination of dull blue and an area fluorescing very brightly. If one wants to try to collect a sample of blood for subsequent DNA analysis, try to swab the areas fluorescing a dull blue.” – E.M. Robinson et al., 2017. ScienceDirect. Source
8. Red Blood Cells (RBC) vs White Blood Cells (WBC)
As can be verified from the further below mentioned sources, the main (and most relevant) differences between RBCs and WBCs are:
1. Size: RBCs are much smaller than WBCs – RBC (±7.5µm ) being about half the size of WBCs (±15 µm)
2. Number of cells: RBCs = 5 million RBCs in every cubic mm of blood / WBCs = 3 000 – 7 000 WBCs in every cubic mm of blood (WBCs account for only about 1% of blood’s cell constitution and there are about 600 RBCs for every one WBC)
3. Shape: RBC = Biconcave (like a disc) / WBCs = No set shape but mostly irregular
4. Rouleaux Formation: RBCs = Yes / WBCs = No [Rouleaux formation refers to the stacking of four or more red blood cells – thus they can clot together, aided by the flatter surfaces of their biconcave shape]
5. Lifespan (in circulation): RBCs = ±120 days / WBCs = 5 to 21 days
6. Motility: RBCs = Non-motile (but can move through circulation) / WBCs = generally motile
7. Cell membranes: RBCs = Smooth / The undeformed WBC has many convoluted folds on its surface
8. Deformability / Flexibility: Apart from its larger volume (size) WBCs are less deformable than RBCs, and RBCs are thus more flexible than WBCs Compositions: The granules of WBCs (Neutrophils, ±50% of WBC count, contain lysozymes (enzymes that breaks down cell walls.)
Some sources for points under 8.1:
https://pdf.sciencedirectassets.com (‘Passive mechanical properties of Human Leukocytes’)
9. Porous vs Non-Porous Material
9.1 “Hard surfaces are a combination of porous and nonporous materials. Common hard-surface materials are stainless steel, solid surface, laminate, porcelain, and a wide variety of tile and ridged plastic materials. Some of the more common porous surfaces include laminate, granite, and various types of tile and plastic materials. [. . .] While there are nonporous hard-surface materials such as stainless steel, solid surface and some rigid plastic materials, other commonly used materials such as laminate, granite and some plastic materials are porous.” L. Lybert, 2016. Health Facility Management. ‘Porous and nonporous hard surfaces’. Source
9.2 “Stainless steel is also non-porous which further increases its resistance to corrosion.” Source & Read more about stainless steel here
Author’s Note: While it may depend on its composition and manufacturing, generally rubber would be considered to be porous (or at least more porous than steel). It must be noted, as can be researched, that the pores in a substrate that is considered to be porous, although they may appear perfectly smooth and hard, can be microscopically small.
Some references to porousness:
What has to be mentioned and appreciated foremost is that both haemoglobin and DNA are contained within cells. Haemoglobin, which contains the iron that reacts with Luminol, is found within the red blood cells and DNA (w.r.t. to blood) in the nucleus of the white blood cells. Neither hemoglobin nor DNA are omnipotent, indestructible loose “creatures” with fangs that hook onto anything and everything without having the ability to be removed from it. Firstly, they are in cells, thus, if you remove the cells, as a result, you automatically remove the haemoglobin and DNA too.
Obviously different cells may retain differently on different substrates. But they also have no special clinging abilities. Loose epithelial cells (which also contain DNA) on a non-porous surface such as steel will be easier to remove than red or white blood cells from porous or non-porous surfaces, also due to the stickiness of blood (due to its sugar content). However, the point remains, if you remove the cells you remove the source of haemoglobin and DNA.
While Castelló et al., 2009; 2010 (refer to 4.1) seems to “revise” a previous finding that products containing active oxygen can prevent positive results from being found using presumptive and human haemoglobin tests – or at least they followed the previous study up with a study that found that DNA profiles can still be obtained after treatment with such products. However, there are enough other studies to suggest that blood (i.e. at least haemoglobin) can even be washed off objects with water alone – refer to the study by Creamer et al., 2005, where blood-stained tiles were repeatedly washed with water, and that after ten washes no reaction with Luminol was be produced. (Refer to 4.3)
It can therefore be deduced that if blood (i.e. haemoglobin carrying cells) can be washed from tiles with water to the extent that it can longer be detected by Luminol, then blood can also be washed from the bare steel parts of a hammer with water so that it does not react with Luminol. [Considering also that tiles are more porous than steel.]
In a study investigating the effect of bleaching agents on the DNA analysis of bloodstains on different floor coverings, Edlar et al., 2020 states that “cleaning smooth surfaces with water is usually sufficed to prohibit retrieving a DNA profile in most of the cases” and that on carpets (a particularly absorbing substrate), “retrieving partial or complete profiles after the use of bleaching agents was only possible when cleaning with low concentrations of 3% hydrogen peroxide.” (Refer to 4.4)
Let us look at Section 6 of this document: It is clear that soaps and detergents break down the lipids in cell walls – and that DNA is subsequently released from the cell. This forms part of a routine DNA extraction process. When released, the DNA would unwind and can become grouped – so much so that it is visible with the eye. Furthermore, DNA is soluble in water (unlike in alcohol). Thus, the DNA strands (now loose and unwound) can offer resistance and there can be no reason why they cannot be wiped of a non-porous surface such as stainless steel after the object was soaked in water with even dishwashing liquid – more so if done repeatedly.
Without going into much detail regarding the difference between the reactions of blood vs bleach with Luminol (more can be read here) – bleach will normally glow brighter and longer than blood, which gives a dull and shorter glow. This will also depend on the substrate – i.e. on steel vs a sponge, as on steel more of the haemoglobin will be “on” the surface and will therefore be more exposed to glow.
With regards to this specific case (involving the ornamental hammer), without going into any further merits of the case, it has to be mentioned that after treatment with Luminol the analyst perceived the intensity and duration of glow (on the rubber part only) to be suggestive of blood, and she testified in Court with confidence that it was her opinion that the reaction was indicative of blood rather than anything else.
Regardless, let us look at all (or most of the known) substances that can react with Luminol, albeit with different intensities and durations: blood, faeces, urine, horseradish, copper-containing chemical compounds, excessive smoke in an enclosed space, furniture polish and certain paints.
Given the history (in short) that the hammer was for all intent and purposes a new and unused hammer (although it was bought years prior but was in its box in a closet for some time), before it was given to the accused as a Christmas gift by the victim – and given that (on the accused’s version) that the hammer was in a protected environment (behind his vehicle’s seat) for three months, because he “forgot it there”, and that it was never used, the question arises: Why was there any reaction with Luminol? – given the list mentioned above; what would any possible and reasonable explanation be for the presence of any of those substances on the hammer? The best estimates would be either blood or bleach – the latter which, as have been shown, can be used to clean blood from surfaces – but bleach is volatile and, and after some time is more unlikely to react with Luminol than with traces of blood.
The hammer was then analysed for DNA – but none of the victim’s DNA was “found” on the hammer. Only the DNA of the accused was found on the hammer. Which was not surprising – as after the police discovered the hammer behind his vehicle’s seat, they asked him to take it out from behind the seat – so he touched it with his bare hands (which would have transferred his DNA via sweat to the hammer*). What is strange however, is the lack of any other DNA. The accused’s name was engraved in the stainless steel shaft of the hammer only 2.5 months before; so, where was the DNA of the engraver? [*While ‘pure’ sweat does not contain DNA, it collects and carries loose epithelial cells to be transferred by touch onto objects and surfaces.]
It has to be emphasised that the Luminol reaction was only on the rubber handle, which has little indentations in it. The rubber handle was also not removed to swab the underlying steel part or the inside of the rubber handle.
Given what has been discussed and shown (by literature) to have cleaned stainless steel part of the hammer from haemoglobin and DNA would have been possible, and in fact easy – by repeated washes by dishwashing liquid and or bleaches. We eat with stainless steel cutlery every day because it can be washed cleanly – i.e. from bacteria (also cells) and fat. This doesn’t mean that a blood-stained stainless steel knife will test negative with Luminol after one wash – but most possibly do so after repeated washes, and more so with drying periods in between washes. It must be borne in mind that UV light also degrades DNA and that repeated washes with drying periods in sunlight between washes, could have assisted in destroyed any evidence of DNA on the steel parts. With regards to the rubber handle, with the little indentations in for ensuring a better grip, because Luminol is extremely sensitive, and because it would be more difficult to remove blood completely from the microscopic pores in the rubber and the indentations in it, it is understandable that while there may have been a reaction with Luminol, it does not mean that that the blood still contained DNA. Only 1% of blood contain DNA and given the fact that soaking the hammer in soaped water (water which is extremely penetrable into all nooks and crannies), which would have broken the cells open to release the DNA, it is quite comprehensible that no DNA of the victim could be retrieved from the object, as the released and untangled DNA strands (now offering resistance) could be washed and wiped off from the object just as you would wipe off anything else that would offer some resistance, for example, even a fine grain of salt.
A reasonable question would be: Assuming that it was indeed blood that was detected by Luminol – which means not all red blood cells have been removed – why were no white blood cells (thus DNA) of the victim found?
For this we need to revisit Section 8, and for a start to again look at Figure 3, duplicated as Figure 5 below.
1. There are much more RBCs than WBCs and while it may stay relative, after a thorough wash with soaps and/or detergents (and after repeated washes) very little if any WBCs may have been present, also for the following reasons:
2. WBCs are bigger than RBCs, are more irregularly shaped, with a rougher surface than RBCs. On basic logic it will follow that a bigger, less flexible, a more irregular shaped particle with a rougher outer surface (which all increases resistance) would be easier to wipe/remove from a surface, than a smaller, smoother, more flexible particle that (even on size alone) can be protected in the microscopic pores in the rubber.
3. There are further differences between RBCs and WBCs which would be difficult to extrapolate from blood in the circulatory system to blood on an external object, but it has to be noted that in the circulatory system WBCs has a shorter lifespan than RBCs, RBCs can clot together (Rouleaux formation) and are less motile than WBCs.The granules of Neutrophils (±50% of WBC count) also contain lysozymes (enzymes that breaks down cell walls).
When we look at Fig. 5 above, the question is: Which would be the easiest to remove: the smaller, flatter, smooth red cells or the bigger and rougher surfaced white cells – with, say, wiping an object with these two kinds of cells on it, with a rough piece cloth? Best is to imagine hundreds of very fine dried paint spots on a glass pane – but with a few bigger spots dispersed among them. When you take a dry (or wet) cloth and wipe over the glass pane in order to clean it, which spots will be removed the easiest? The bigger ones. Even while they may have greater surface contact – they offer more resistance against the cloth – therefore a force can be applied to them to move them, less so with smaller spots. Now imagine the same scenario; replacing the fine paint spots with RBCs and the bigger spots with WBCs (which is double the size of RBC and with a more rigid structure and rougher outer surface). Which will be wiped off easier?
Like in any case, it may also depend on sampling. How well was the rubber swabbed? All of it or only a small part of it? Absence of evidence is not evidence of absence.
Which brings us to the point of blood as source of DNA. Even in “fresh” blood pools, the WBCs settle out quickly (due to the bigger size, and therefore weight, it will settle at the bottom of the pool) and WBC apoptosis* can occur quickly: neutrophils within 24 hr, lymphocytes by 72–96 hr, and RBCs haemolysis [rupture or destruction of it] can result in low and degraded DNA yield. Platelets and WBCs can clot and form masses which is difficult to extract. The best source is small drops that dry quickly, where the cells are rapidly fixed due to dehydration. – Dr Karin Shires.* 2017. UCT Lecture notes (PP). ‘Types and sources of DNA’. [*Senior Medical Scientist (Haematology), National Health Laboratory Service (Groote Schuur Hospital /UCT)]
*Apoptosis is a form of cell death, also known as programmed cell death, in which a ‘suicide’ program is activated within the cell, leading to fragmentation of the DNA, shrinkage of the cytoplasm, membrane changes, and cell death without lysis or damage to neighboring cells. It is a normal phenomenon, occurring frequently in a multicellular organism.” Source
This all brings us back to the following:
1. After death cells die off and this, together with other factors (such as environmental factors), may cause the degradation of DNA at an early stage already.
2. It depends on how the sample was collected. With one or two swabs of a suspected area, it is quite possible to “miss” the collection of WBCs (especially considering there are 600 fewer WBCs than RBCs) – more so if the area was thoroughly cleaned.
3. If you remove the cells you remove the source RBC or WBCs – and when WBCs are removed its DNA is removed with it.
4. DNA can be released from the WBC by soaps – which then unwinds into ‘something’ significant enough (which can offer resistance) to be washed and/or wiped off from an object or surface.
Given the reasonable deductions made from referenced sources – as well as applying deductive and logical reasoning – a reasonable conclusion can be made that it is possible to clean such a (blood-soaked) hammer to such an extent that all white blood cells (and thus DNA) are removed, or at least to the point of being undetectable, while enough red blood cells may remain to react with Luminol.
Therefore, the absence of a victim’s DNA on an object does not mean it was not used in an attack.
Post Scriptum by the Author
With reference to the two studies by Castelló et al., 2009; 2010: (Refer to Section 4):
Without having scrutinised the two respective articles thoroughly – it stands out that the first study (which on the face of it seems more comprehensive than the second study), the authors conclude: “The results show that regardless of the type of blood used to generate stains, the age or backing on which they were placed (soft cotton cloth, jeans fabric, toweling) or the washing conditions employed (hot or cold water), washing fabric with products containing active oxygen prevents positive results from being found using presumptive and human haemoglobin tests.” They do not say anything about DNA profiling but in the article pertaining to the second study mention that: “These findings [of their previous study] have caused considerable concern both within the forensic and scientific community, and among the general public, so obliging us to seek solutions.” The finding of the second study is that DNA profiles can be obtained after washing/cleaning items with products containing active oxygen.
Without suggesting that “the public concern”, which “obliged them to seek solutions”, may have led to bias in their second study – there is a suggestive aspect to it that public domain information of this nature (i.e. that blood and DNA can be removed to an untraceable level) poses a danger for society – because by reading about this, criminals can now cover their tracks by destroying evidence, such as blood and DNA from surfaces and weapons, which may otherwise implicate them.
This may be true but there is a flip side to it. If, and I repeat if, it is a proven fact (proven by robust studies) that blood and DNA can be totally (or to an untraceable level) be removed from an object (porous or non-porous), then we as forensic scientists should know it and acknowledge it. Scientific studies and findings cannot be driven by “public fear”. The flip side is that it affects argument in court. If the “fact” that blood and DNA cannot be removed completely from bloodied items, prevails, it may cause a murder weapon (with no blood or DNA on it) to be thrown out as evidence while there may be other factors that could suggest that specific object as the murder weapon. For example, based on the size and shape of a knife and how it relates to the wounds or imprints that it may have left on the scene, may simply be ignored because “no blood or DNA was found on it”. If it is a proven fact – or even highly possible – to remove blood and DNA completely from blood-stained objects, that argument/fact should be able to be levelled in court, and evaluated with other possibly corroborative evidence pertaining to the object/weapon.
In this particular case – where the ornamental hammer was implicated as the murder weapon – the “fact” that “no blood and DNA of the victim was found on it” played an instrumental role in dismissing it as the murder weapon. (While “inconclusive” for blood and because no DNA was found, the judge incorrectly stated in his judgement that “there was no blood the hammer”. What was not “found” was the victim’s DNA.) This perception – still prevailing today, even among forensic scientists – that blood and DNA cannot be removed from an object – played a crucial part in the judge dismissing the hammer as the murder weapon.
Returning now to the comment about corroborating evidence. In this particular case, a towel was found in the victim’s bathroom and it is clear (by for example blood and hair on it) that the murder weapon was wiped clean with it straight after the murder. Subsequently, official SAPS photographs have shown (after re-examination by me) imprints on the towel that perfectly resembles parts of the fairly uniquely shaped tail of the hammer (which is also a scarce item), including the bottle opener ring (see photo’s here). Photos of the hammer’s tail also show that it was possibly deformed slightly. While there is no ‘before and after’ photos to make a conclusive statement regarding this, it certainly looks deformed vs what one would expect a new one to look like. Also, the hammer was found under suspicious circumstances in the vehicle of the accused – who would put a Christmas gift of your girlfriend under your vehicle’s seat for no good reason? The size and shape of both ends of the hammers head are also reconcilable with the two types of head wounds (circular and linear) and the diameter of a depressed fracture on the frontal skull bone matches the diameter of the implicated hammer 100% (20 mm, which is also a relatively uncommon size for a hammer). While all of this was disputed, of course, as is needed in an adversarial system – the fact that no DNA of the victim was found on the hammer, played a crucial role in dismissing a weapon, that could on other factors be linked to the crime.
What is ironic, and with this I want to make some remarks about the general overestimated evidentiary value of DNA: In this particular case, even if the victim’s DNA was found on the hammer, the defence could (and rightly so) could have argued that it was to be expected, since the victim would (or may) have handled the hammer before the murder. After all, she gave it to him as a present and one would expect her to have handled it at some time.
People have been wrongfully convicted on DNA evidence – such as Lukis Anderson whose DNA was found on (not under) the nail of a murdered victim – but it was later postulated that the DNA was transferred to the victim’s nail by accident, by paramedics having slipped the same pulse oximeter (which slips over the finger) over both Anderson and the victim’s fingers the same night of the murder. (Anderson was taken to hospital by an ambulance at the time of the murder, for over-intoxication, and just after that, the paramedics went to check the vitals of the victim whose house was relatively close to the hospital.) There was nothing else that linked Anderson to the murder, but based on the DNA evidence he spent some time in jail and faced the death penalty. He was acquitted though after evidence started to point at other suspects. Read about this case and some very interesting similar cases and about DNA evidence in general (about its positives and negatives) in this very interesting and very comprehensive article.
To conclude, as valuable as DNA as evidence can be and is (mostly), it is not the golden bullet in all cases – and must be treated with caution and viewed in conjunction with other evidence. It is perhaps an area that needs more research, but based on arguments presented in this document, which are based on the literature, at the very least we must start adopting the belief that blood and DNA can possibly be removed completely (or to an untraceable degree) from objects, albeit not equally from all objects.
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