The world of forensic science is a wide vista of seemingly disparate subjects encompassing many scientific disciplines, the arts, and law. Where once the term "forensic science" was used only by specialists, it is nowadays a familiar household phrase. So, from time to time, we'll be populating this page with a forensic science FACT of the DAY and in doing so, hope to explain or demystify many of the terms you'll come across in the big world of forensic science.
MAY 2020 | ||
14th | FINGERPINTS: | The Henry system for the classification of fingerprints introduced in the early years of the 20th century has been used successfully for over a hundred years in virtually every county in the world. Despite this, it has one important limitation: it can be applied only when the pattern types for all ten digits are known. A single finger identification system, perhaps the most successful system, was invented by fingerprint expert Superintendent FREDERICK CHERRILL of Scotland Yard, and introduced in 1930. Perhaps anecdotal, but it is cited that Cherrill, head of Scotland Yard's Fingerprint Department from 1938 to 1953, solved more murders than any other detective of his era in his 39 years with the Yard. Apparently, he could glance at an inked pattern of ridges and whorls and tell from memory the owner of the prints. |
13th | POLICE: | To do with VEHICLE CRIME:
The acronym TWOC arises out of the wording of S12 Theft Act 1968 to describe any unauthorised use of a vehicle that is not an actual theft, that is, taking a vehicle without the intention of permanently depriving the owner of the vehicle. And the reason? Because it is easier to prove unauthorised use than theft (where the intention is to permanently deprive the owner of their possessions). |
MARCH 2020 | ||
6th | QUOTATIONS: | “The ear, thanks to these multiple small valleys and hills which furrow across it, is the most significant factor from the point of view of identification.” ; "It is, in fact, almost impossible to |
5th | QUOTATIONS: | “Next to fingerprints, the external ear constitutes the most unique design, characteristic features and peculiarities for the purpose of identification. On no other part of human body do we have flesh lines with such a unique design”. Alfred V. Iannarelli in Ear Identification, Forensic Identification series, Paramont Pub, 1989 |
4th | BIOMETRICS: | Dr Imhofer,"ear" doctor from Prague took the first steps towards a system of identification for ears in 1906. He observed that "…. the combination of three ear characteristics could be found once only in 500 subjects" and"….. the characteristics of the human ear remain unchanged during the whole of a person’s life." Imhofer R. Die Bedeutung der Ohrmuschel für die Feststellung der Identität. Archiv für Kriminal-Anthropologie und Kriminalistik 1906; 26: 150–63 |
1st | POLICE: | Every profession has its acronyms. Some POLICE ACRONYMS to do with vehicles:
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FEBRUARY 2020 | ||
28th | FINGERPRINTS: |
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27th | QUOTATIONS: | "In solving a problem of this sort, the grand thing is to be able to reason backwards. That is a very useful accomplishment, and a very easy one, but people do not practise it much. In the every-day affairs of life it is more useful to reason forwards, and so the other comes to be neglected. There are fifty who can reason synthetically for one who can reason analytically...Let me see if I can make it clearer. Most people, if you describe a train of events to them, will tell you what the result would be. They can put those events together in their minds, and argue from them that something will come to pass. There are few people, however, who, if you told them a result, would be able to evolve from their own inner consciousness what the steps were which led up to that result. This power is what I mean when I talk of reasoning backwards, or analytically." Found in Chapter 7 (Conclusion) of A Study in Scarlet. |
26th | THINK FORENSIC: | A BLIND TRIAL (also called a blinded experiment) is a scientific experiment where some of the people carrying out the experiments are not given information that might influence their observations, findings or conclusions. Consider, for example, whether a forensic scientist examining a blood stain recovered from a suspect to a brutal assault needs to be told that the suspect has previous convictions for assault. BLIND TRIALs are also a means of "validating" the quality of work carried out by a forensic laboratory. In this instance, evidence is submitted to the laboratory as if it is a live case, but the scientists carrying out the work do not know (they are working "blind") that the case is "simulated", and that a particular result is expected. |
25th | FIREARMS: | In the consecutive (sequential) manufacture of tools and firearms, the term CARRYOVER means marks or impressions on one tool/firearm that are exactly reproduced in the next tool/firearm, and the next, and the next... during manufacture. Most firearms experts hold the view that certain methods used to manufacture tools/firearms do not involve CARRYOVER. To put this another way, a premise of toolmark identification is that certain methods of manufacture (grinding, sanding, filing, and polishing) do not produce significant CARRYOVER between consecutively manufactured tools /firearms; in fact, the marks made by these types of "finishing" are typically described as "individualising". |
22nd | PEOPLE: | Dr Rosalyn Sussman Yalow was an American medical physicist who pioneered the radio immunoassay (RIA) method for the measurement of trace substances (such as drugs, hormones and viruses) in human body fluids. In 1975, she was awarded the AMA Scientific Achievement Award together with co worker Dr Solomon Aaron Berson (who had in fact died in 1972), and in 1977, the Nobel Prize in Physiology or Medicine in 1977, together with Roger Guillemin and Andrew V. Schally. Yalow was the second American woman to be awarded the prestigious Nobel Prize in Physiology or Medicine. In the forensic context, RIA can be used to routinely measure trace amounts of drug in human hair. |
21st | THINK FORENSIC: | In any scientific measurement, PRECISION can be defined as "the reproducibility of a measurement." PRECISION describes the difference among individual measurements; if they are close together, the precision is high whereas if they are scattered, the precision is low. It is always true that there is some difference, albeit a very small difference, when measurements of the same thing are repeated. These differences are simply a consequence of the natural uncertainty (see UNCERTAINTY - 11th January 2013) that exists in every measurement. |
20th | POLICE: | The acronym VASCAR means Visual Average Speed Camera And Recorder. This device, first created by Arthur Marshall in 1966, is used by police officers to measure the speed of a moving vehicle and enforce speed limits. The speed-determining device originally designed by Marshall was entirely mechanical whereas nowadays it is of course microprocessor driven. In essence, VASCAR is a sophisticated stopwatch employing radar which records the time a vehicle takes to move between two fixed points, the distance between having been previously and accurately (ACCURACY - see 15th February 2013) measured by the police. For those in the UK, see The UK Speed Trap Guide for more information about speed traps. |
19th | CHEMISTRY: | The RHODIZONATE TEST is a colour test for lead (Pb) particulates expelled from the muzzle of a firearm and found embedded in, or deposited on, the skin of a victim, the surface of a target, or the hands of the shooter. The test involves spraying the forensic exhibit with a weak aqueous solution of sodium rhodizonate (which has a dark yellowish/orange colour). The reagent reacts with any lead (Pb0) and lead (Pb2+) salts turning bright scarlet or purple-blue, respectively. Secondary confirmation involves treatment of the exhibit with dilute aqueous hydrochloric acid and formation of a deep blue colour. |
18th | CRIME SCENE: |
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15th | THINK FORENSIC: | In any scientific measurement, ACCURACY can be defined as "the correctness of the result." The ACCURACY of a measurement describes the difference between a measured (experimental) value and the actual (correct) value. The measured value has low or high accuracy depending on whether the experimental value is, respectively, close to or far away from the correct value. For example, four paint guns each containing a different coloured pellet were used by the same shooter to shoot ten pellets at a blue target on a square grid. The "correct" result is the blue target square. |
14th | CHEMISTRY: | The GRIESS TEST is a colour test for nitrite particles expelled from the muzzle of a firearm which are found embedded in, or deposited on, the skin of a victim, the surface of a target, or the hands of the shooter. The GRIESS TEST uses a solution of sulfanilic acid (4-aminobenzene sulfonic acid), 1-naphthylamine, and acetic acid. When a sample of the suspected gunpowder is mixed with this reagent, the nitrite adds to the sulfanilic acid to form a diazonium compound that reacts with the 1-naphthylamine to form a red azo dye. The brightness of the red colour gives an indication of the quantity of nitrites present. |
13th | POLICE: | In all of the 43 UK police forces, the acronym C&D means "Complaints and Discipline". The London MET branch also uses the acronym CIB meaning the Complaints Investigation Branch. Whether it's C&D or CIB, this function is also more-or-less universally known as the Rubberheel Squad, because you never hear them coming! |
12th | PEOPLE: | The earliest evidence of recorded fingerprints can be traced back around 8000 years to ancient Jericho following a discovery by the archaeologist Dame Kathleen Mary Kenyon. In her book, "Archaeology in the Holy Land (1)", she reported (referring to houses built 7000-6000 B.C.), "The bricks of which the walls were constructed were made by hand (not in moulds, as is usual later), in shape rather like a flattened cigar, with the surface impressed with a herringbone pattern by pairs of prints of the bricklayer’s thumbs, thus giving a keying such as is provided by the hollow in modern bricks." |
11th | CHEMISTRY: | GUN SHOT RESIDUE (GSR) is the trace material deposited on the skin and clothing of the person discharging a firearm. The composition of GSR depends on the type of propellant. Modern, smokeless powders, and black powder contain nitrates. A typical composition might be: Potassium nitrate (65-75%), Carbon, as charcoal (15-20%), Sulphur (10-15%). When the weapon is discharged, large volumes of gaseous carbon dioxide and nitrogen are produced according to the following stoichiometric reaction: 10KNO3 + 8C + 3S → 2K2CO3 + 3K2SO4 + 6CO2 + 5N2
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8th | DEFINITION: | COMMON LAW is law developed by judges arising through decisions they make in courts and tribunals, which sets precedents (basic principles) against which all future legal decisions in similar cases should be based. In principle, COMMON LAW is "common to all similar cases" and should bind all future decisions. For this reason, it is also called case law. The principle that lies at the heart of common law is known as stare decisis, meaning that similar cases should be judged according to common principles. |
7th | QUOTATIONS: | As Sherlock Holmes has it, “It is a capital mistake to theorize before you have all the evidence. It biases the judgment.” Arthur Conan Doyle (1887), A Study in Scarlet , Part 1, chap. 3. The Lauriston Garden Mystery. |
6th | THINK FORENSIC: | In a forensic context, the word PERSISTENCE means the length of time trace evidence remains on the surface to which it was transferred from the time contact and transfer took place. A man wearing a fleecy garment gains entry to a property by breaking a ground floor window using a brick. When the window breaks, tiny fragments of glass fly towards him and transfer to his clothing. Some of these will remain attached to the fleecy fabric of his garment for only a few moments, and some for a considerable period of time long after he has left the scene of crime. If the man is apprehended soon after the crime took place it is likely many of the glass fragments will be present on his garment, and if recovered during forensic examination, these could provide evidence to place him at the scene of crime. |
5th | EVIDENCE: | The CORE is a feature of fingerprints (that are either loops or whorls) around which all other ridge lines flow. The core can be a ridge dot, ridge ending, or the shoulder of a folding ridge (the innermost loop). The precise location of the core is determined using some simple rules:
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4th | POLICE ACRONYMS: | The first police officer attending (FOA) a major crime scene has key duties to perform. The acronym SADCHALETS helps remind them of these duties. The primary duty of the FOA on scene is to make sure that full and appropriate information is communicated to their control room.The key duties are:
The FOA also has other duties to perform which affect the potential for correct preservation and recovery of forensic evidence. |
1st | THINK FORENSIC: | An EVIDENCE TRIANGLE is a useful training instrument for identifying how evidence, people and scenes are potentially linked, and what needs to be done to establish whether or not a link actually exists. For example, A footwear impression is found on the office floor of a burglary scene [so there is a "known", direct association between the impression and the scene] and a suspect has been arrested for the burglary, [so there is a potential, or an unknown, association between 1) the suspect and the scene (?), and 2) the suspect and the impression mark (?)]. We now have the three components of the evidence triangle: the scene; the footwear mark; the suspect, and one known association, and two questioned (?)(?) associations. |
JANUARY 2020 | ||
31st | DEFINITION: | FORENSIC SCIENCE is usually defined as "the application of science to questions of law". We take a complimentary view: FORENSIC SCIENCE is the "science of association". The usual definition emphasises the link between science and law, and says in effect that science, and scientific method are needed to help those who weigh evidence in court arrive at the truth. Our own definition does not focus on law at all, but entirely on what lies at the very centre of the forensic process - being able to show whether or not there is a link (an association) between a person and an item of physical evidence, or between two or more pieces of evidence, and ultimately, between a person and a scene of crime. |
30th | DEFINITION: | To TRADUCE a person is to (malign, smear, falsely represent, slander) give false testimony about them with the intention of causing them humiliation or disgrace, or to besmirch their good character. Examples are:
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29th | SCIENCE DEFINITION: | The word DEDUCE means to reason out, or to derive, or to infer, or to understand ... the true meaning of something from available information. It is a method of reasoning in which a conclusion follows from the stated information. In scientific enquiry, deduction is a key part of scientific method, where all available information (the experimental data) is critically weighed before reaching a conclusion. The process of deduction starts with a set of facts (or possibilities) and reduces these to the smallest possible set of possibilities. The investigation of crime, for example, starts with a collection of information and reduces to the point where a suspect to the crime can be identified. Other examples are:
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28th | LAW DEFINITION: | The word ADDUCE is often used by legal professionals and it means simply to present, or to offer, or to introduce, or to bring forward, or to draw out .... evidence in support of an argument. Examples:
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25th | CRIME SCENE: | When a crime scene examiner recovers physical evidence, it is essential that the INTEGRITY of the evidence is maintained. This means doing everything necessary to preserve the evidence in exactly the same condition in which it was found from the moment of recovery through every stage of forensic and legal enquiry until it is finally destroyed or returned to it's owner. This outcome is usually achieved by use of the most appropriate methods of recovery and packaging. |
24th | THINK FORENSIC: | How many damage features on the sole of a shoe are sufficient to make a FOOTWEAR impression (from that shoe) unique? Just one damage feature can be sufficient. Every damage feature has four possible characteristics: its shape, its size, its position, its orientation, which combined, make each damage feature unique. Is it possible for another shoe having the same sole size and pattern to exhibit a damage feature having exactly this same combination of characteristics? Well, it might seem utterly inconceivable, but the possibility cannot be completely ruled out. It has just never been observed before. Indeed, the likelhood may be as probable as a chimpanzee playing a tune on a piano given a sheet of music to read! But that's something else altogether! |
23rd | CHEMISTRY: | WOOL fibres are naturally-occurring polyamides (Amides: see NYLON, 15th January 2013) comprised of a large number of proteins (amino acids connected together by amide bonds). Many of these proteins are cross-linked to one another through covalent (shared electron) sulfur-sulfur (S-S; disulphide) bonds making them very stable, and essentially resistant to biological decay. Such cross-linked proteins are known as keratins. These proteins are assembled into a complex structure which (in the very simplest of terms) is comprised of a central core (the cortex) surrounded by a layer of overlapping scales (the cuticle). Both the cortex and the cuticle are themselves assemblies of other cellular sub-components. All hairs (whether of human or animal origin) share these same general chemical and physical features, yet they can be forensically distinguished by both chemical and microscopic examination. |
22nd | QUOTATIONS: | EDMOND LOCARD (1877-1966) is often cited as saying "Every Contact Leaves a Trace". What he actually said was "Toute action de l’homme, et a fortiori, l’action violente qu’est un crime, ne peut pas se dérouler sans laisser quelque marque.” [ Source: page 8, La Police at Les Méthodes Scientifiques (1934) ]. Translated to English, this becomes, "Any action of an individual, and obviously, the violent action constituting a crime, cannot occur without leaving a trace." The essence of his remark is indeed "Every Contact Leaves a Trace." |
21st | THINK FORENSIC: | In the context of crime scene and forensic laboratory examination, CONTINUITY means maintaining an unbroken, documented record / paper trail of the movement and possession of physical evidence (the exhibit) from cradle (its recovery) to grave (its disposal). The consequences of not maintaining CONTINUITY are severe: the probative value of the evidence can be completely destroyed. |
18th | EVIDENCE: | There are 12 distinct character-types of human hair based on their site of origin: scalp, eyebrow, eyelash, ear, nose, beard, chest, limb, axillary (underarm), pubic, vulvar, and buttock. Each has a different gross appearance and when viewed microscopically. A forensic scientist who examines human hair must be able to distinguish between these types. Scalp hair, for example, is typically characterised as having a diameter in the range 25-125 microns with little variation along the fibre length, a small root, a tapered tip, often cut or frayed, and a variety of types of medulla. Scalp hairs grow at a rate of approximaely 0.4 mm per day, and of course are frequently observed to have been artificially treated. |
17th | QUOTATIONS: | Holmes on Crime: "No, no. No crime," said Sherlock Holmes, laughing. "Only one of those whimsical little incidents which will happen when you have four million human beings all jostling each other within the space of a few square miles." Found on page 1 of the 7th short story in the Adventures of Sherlock Holmes; Adventure 7: The Adventure of the Blue Carbuncle. |
16th | POLICE ACRONYMNS: | HOLMES, introduced in 1985 to the UK, means Home Office Large Major Enquiry System. Currently at version 2, HOLMES is a computerised information technology system which provides a single, integrated system for all of the 43 UK police forces, and the Royal Military Police to facilitate a cross-boundary, coordinated approach to the investigation of major incidents such as serial murders and very large scale fraud, and the management of disasters. |
15th | CHEMISTRY: | NYLON is a man made polyamide first prepared by Wallace Carothers in 1935 at the Dupont Experimental Station based in Wilmington, Delaware, US. Strictly speaking, NYLON is a class of polymers all of which are long-chain molecules containing many amide groups (-NHCO-) repeating along the chain. There are various chemical approaches to making polyamides of which the archetypal reaction is between substances containing the amine (-NH2) group and the carboxylic acid (-CO2H) group. A convenient nomenclature (naming system) for NYLON is based on the number of carbon atoms in the monomers (the building blocks) that are used to make the polymer. Nylon 6, for example, contains 6 carbon (C) atoms in the repeating unit: -[NH(CH2)(CH2)(CH2)(CH2)(CH2)CO]- Nylon 6,6 contains 6 carbon atoms in each of the two monomers that were used to make the polymer (6 in the diamine part, and 6 in the diacid part): -[NH(CH2)6)NHCO(CH2)4CO]- And Nylon 6,10 contains 6 carbon atoms (from the diamine part) and 10 carbon atoms (from the diacid part): -[NH(CH2)6NHCO(CH2)8CO]-
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14th | EVIDENCE: | A DELTA is a feature of fingerprints that are either loops or whorls. It is that part of the fingerprint that looks most like a triangle and it gets its name from its similarity to the delta of a river outlet flowing in to a lake or the sea. There is one DELTA in every loop and at least two DELTAs in every Whorl. The precise location of the DELTA (D in the image) can be a single ridge dot, a ridge end, a bifurcation (where a single ridge divides in to two separate ridges), or a point along a continuing ridge; nomatter which, all are located at a position lying centrally beween the place where the fingerprint type lines (Ridges A and B) diverge, and towards the middle (core) of the fingerprint. |
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11th | THINK FORENSIC: | In every scientific measurement, there is a degree of UNCERTAINTY, defined as the difference between a measured value and the true value. For example, a batch of some powder may weigh exactly 5 grams, but the balance used to make the measurement may not be able to "tell the difference" between something weighing 4.999 grams and 5.001 grams, so there is an UNCERTAINTY of ± (plus or minus) 0.001 grams (1 microgram) in the measurement. Or the width of a fibre may be found to lie between 60.01 and 60.05 microns, so the measurement would be reported as a width of 60.03 ± 0.02 microns. Being able to quantify uncertainty in scientific / forensic measurement is a necessary part of laboratory casework. |
10th | SECURITY: | The first major incident of the forging of UK denomination notes occured in 1695 when a Daniel Perrismore was fined for transcribing (copying) sixty, £100 pound BANKNOTES (Rastan.C 1996, "Not So Funny Money, Curbing The Counterfeiters", Crime Prevention News, March, pp 17-19). In 1697 this incident of counterfeiting led not only to the use of watermarked paper, but it led also to counterfeiting of banknotes being made a felony punishable by death. |
9th | EVIDENCE: | A LATENT MARK is one not normally visible to the unaided human eye, but has the potential to be revealed. A latent fingerprint, for example, is completely invisible on most* surfaces, but can be made visible (the correct technical term is "developed") either by applying:
* Latent fingerprints on smooth, glossy surfaces can often be observed without "development" by using reflected light illumination: the fingerprint appears as a non-glossy pattern against a reflective, glossy background. |
8th | FORENSIC TEST: | A FALSE NEGATIVE occurs when a test fails to reveal the presence of a substance that is actually present. The result can occur when 1) the test of choice is not sufficiently sensitive for the substance being tested, or 2) when chemical reagents used in the test have become "spent" (they have deteriorated) or 3) when other substances that suppress the reaction are are also present. For example, stains of what appear to be smears of blood on a garment could be sampled and tested using the two-component LMG (leucomalachite green and peroxide) test for blood; the test should yield a pale turquoise colour if blood is present. However, if the levels of peroxide have diminshed because the test reagents have exceeded their useful "use-by" date, the formation of a turquoise colour may never occur, and the forensic examiner could conclude (incorretly) that the stains are not blood even though they have the appearance of blood. |
7th | CHEMISTRY: | ELISA, meaning Enzyme-Linked Immuno-Sorbent Assay is an immunochemical test to detect the presence of specific substances (see 17th December 2012), and can be used by toxicologists as a rapid, presumptive screen for the presence of drugs in forensic samples. ELISAs are described as being "indirect", "sandwich", "competitive", and "multiple and portable" depending on the mode in which the reactants are brought together. The ELISA technique was first developed by Peter Perlmann and Eva Engvall at Stockholm University in Sweden, who published their work in Immunochemistry 8 (9): 871–4 in 1971. In recognition for their work, which has seen phenominal global success as an analytical technique, Perlmann and Engvall were awarded the German scientific award of the "Biochemische Analytik" in 1976. |
4th | THINK FORENSIC: | Bias is a tendancy towards a particular view, and whatever form it takes, it must be avoided by all involved in forensic casework. CONFIRMATION BIAS is a tendancy to 1) look for evidence, or 2) give extra emphasis to findings that support an existing observation or proposition (or belief), or to reject evidence that will weaken the proposition. Confirmation bias can be both intentional and unintentional, and is a very real risk even for scientists who pride themselves on being completely objective. Consider, for example, the situation where a forensic scientist has examined two hairs, one (the "questioned" hair) recovered from the hands of a victim who has been assaulted, the other (the "known" hair) taken from the head of a suspect. and found that the two hairs are indistinguishable (they look the same). After that first "observation", the scientist concludes that the suspect could be the source of the questioned hair. The same scientist now looks at a second, and third and ... samples of known hair. If the scientists then begins to positively look for features in these "known" hairs that "match" those in the questioned hair, s/he has fallen victim to confirmation bias. Of course, proper training, the use of protocols, and blind trials will all go a long way to preventing errors arising from confirmation bias. |
3rd | ANALYSIS: | How many analytical methods should a forensic scientist use to distinguish one sample fragment of VEHICLE PAINT from any other? The answer is: it depends. A fragment of vehicle paint will be comprised of several layers, and those layers could be examined by microspectrophotometry alone (to identify the number of layers and their colour), and this may be sufficient to link that fragment to a suspect vehicle where a "physical fit" is also possible (see 6th December 2012). More often though, the anlysis of vehicle paint requires a raft of methods to be employed which include Fuorier Transform Infra Red Spectroscopy (FTIR), Pyrolysis Gas Chromatography/Mass Spectrometry (PyGCMS), Scanning Electron Microscopy Energy Dispersive X-Ray Spectrometry (SEM-EDXS) as well as microspectrophotometry. |
2nd | EVIDENCE: | The first person to write that fingerprints were unique was the german Doctor, Johann Christoph Andreas Mayer, who in 1788 wrote "Although the arrangement of skin ridges is never duplicated in two persons, nevertheless the similarities are closer among some individuals. In others the differences are marked, yet in spite of their peculiarities of arrangement all have a certain likeness." |
DECEMBER 2019 | ||
21st | PEOPLE: | Paul L. Kirk (see 20th December) was a chemist and one time Teacher who became interested in forensic science after one of his students asked him if it was possible to tell whether his dog had been poisoned. He became Professor of Biochemistry at the University of California, Berkeley (in 1929), and was involved in several forensic cases, most notably that involving a rape case and the identification of the perpetrator from fibre evidence. He became leader of the university’s criminology programme (1937), and because of his extensive microscope work, was an invited contributor to the Manhattan Project to isolate fissionable plutonium (1942-45). After the war he returned to Berkeley and was established as the university’s Professor of Criminalistics. |
20th | QUOTATIONS: | Whereas Edmond Locard is often thought of as the father of forensic science, it was Paul L. Kirk who elevated the discipline to one that was more mature than in Locard's day when he said .. "“Wherever he steps, whatever he touches, whatever he leaves, even unconsciously, will serve as a silent witness against him. Not only his fingerprints or his footprints, but his hair, the fibres from his clothing, the glass he breaks, the tool mark he leaves, the paint he scratches, the blood or semen he deposits or collects. All of these and more bear mute witness against him. This is evidence that does not forget. It is not confused by the excitement of the moment. It is not absent because human witnesses are. It is factual evidence. Physical evidence cannot be wrong, it cannot perjure itself, and it cannot be wholly absent. Only its interpretation can err. Only human failure to find it, study and understand it can diminish its value.” |
19th | EVIDENCE: | When two people come in to close contact, trace evidence like hairs and fibres can be passed from one person to the other. This is known as direct (or primary) transfer because the transfer that takes place occurs directly, without one or more intermediate persons being involved. Trace evidence can also be transfered indirectly between two people via a third (intermediate) person; transfer of this type is known as SECONDARY transfer. It is important to consider the whether primary or secondary transfer of trace evidence has taken place when forensically interpreting the significance of the evidence. |
18th | FORENSIC TEST: | A FALSE POSITIVE occurs when a test demonstrates the presence of a substance that is actually absent. The result can occur when a benign substance mimics the chemical effect of the targeted substance on the test. A test for heroin for example can be positive when the donor of the sample (such as urine) has consumed significant quantities of poppy seeds. |
17th | CHEMISTRY: | IMMUNOASSAYS are chemical tests used to detect or measure the amount of a specific substance in a sample such as blood or body fluid. The tests are both highly sensitive (they can detect extremely small amounts of the target substance), and highly specific (they can detect the presence of a precise target substance). In forensic casework, immunoassays are typically used to detect or quantify drugs, whereas in medicine, immunoassays are used to measure the presence of substances such as hormones, proteins, and markers of cardiac injury, and disease. |
14th | FORENSIC TEST: | The location of a SALIVA stain on a garment recovered for forensic examination is detected using PHADEBAS reagent in what is called a press-test - because the test involves the use of a sheet of highly absorbent paper pressed directly on to the area where the stain is thought to be. The test is presumptive (see 8th November) and detects a-amylase, an enzyme found in high levels in saliva. The absorbent paper, contains microscopically small spheres of starch to which a water-soluble blue dye molecule is chemically linked. If a-amylase is present in the stain, the starch is digested, and the water-soluble dye is released into the paper forming a blue zone having the same shape as the saliva stain over which the test paper was pressed. |
13th | LAW: | A DAUBERT HEARING is a pre-trial evaluation of "expert" evidence made (in the US) by a judge to determine whether the expert's testimony is based on sound reasoning that is scientifically valid. Daubert (pronounced DOW-BERT) hearings are intended to identify and keep out "bad" science from the courtroom. An expert's tesimony/evidence is considered scientifically valid if the method used to gather the evidence: |
12th | CRIME SCENE: | When blood is shed as a result of an assault, the resultant blood stain pattern can be analytically evaluated to reveal a wealth of information about the circumstances of the assault. Blood Pattern Analysis (BPA) can reveal:
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11th | CHEMISTRY: LUMINOL | LUMINOL is a chemical that can be used to detect trace amounts of blood too small to be easily observed at crime scenes. The reaction involves iron (Fe) in the haemaglobin of red blood cells, which acts as a catalyst (it "kicks" the reaction); it takes place under basic condition in the presence of an oxidising agent (hydrogen peroxide) and proceeds at room temperature with the emission of blue light. Because light is emitted, it is an example of a chemiluminescent reaction (see post below - 10th December). The blue emission spectrum is made up from two major light bands: at 424 nm and 485 nm. The "luminol" reaction is also used by biologists in cellular assays for the detection of copper, iron, and cyanides. |
10th | CHEMISTRY: | CHEMILUMINESCENCE is a property of materials that emit light as a result of a chemical reaction in which unstable, "excited" products are generated; these then form more stable products and in doing so, release energy in the form of light. Chemiluminescent reactions can be grouped into three types:
Light sticks (or glow sticks) used by everyone from party-goers to emergency service personnel, and the flashing emisions from the tails of glow flies are examples of chemi- / bio- luminescent reactions. |
7th | EVIDENCE: | A HOLAB form was an old-style Home Office Laboratory submission form used by the police to present details of the circumstances of a crime and physical evidence recovered from the crime scene, when those items of evidence were submitted to the receiving laboratory for forensic examination. The HOLAB form was replaced with the MGFSS (manual of Guidance Forensic Science Service) form A (Submission of Case for Scientific Examination) and MGFSS Form B (Items for Forensic Examination) for submission of evidence to Forensic Science laboratories. Around 2004, these forms were re-branded to MGFSP (Manual of Guidance Forensic Science Provider). These, and other MG forms are used by the police to record information during the investigations of crime. |
6th | PHYSICAL EVIDENCE: | A PHYSICAL FIT is defined as the joining of two pieces of physical evidence in a manner which shows that they were orginally the same item. A physical fit is the outcome if a fragment of glass recovered from the scene of a hit and run motor incident can be physically fitted in to the broken lamp glass of the recovered vehicle. This shows that the vehicle will have been the source of the glass fragment at the scene. A physical fit is the outcome if the various parts of a shredded document can be reassembled to create the original, intact, document from which they were formed. |
5th | QUOTATIONS: | As Holmes would have it, "Crime is common. Logic is rare. Therefore it is upon the logic rather than upon the crime that you should dwell." The quotation can be found on p1 of Adventure XII. The Adventure of the Copper Beeches, the 12th in the series "The Adventures of Sherlock Holmes," written by Sir Arthur Conan Doyle. The Adventure can be read, for free, at Page by Page Books. |
4th | ANALYSIS: | Determination of trace amounts of water in materials is big business, so how is water content measured? Perhaps the best known is the KARL FISCHER method named after its inventor, Joseph Karl Anton Fischer (1901-1958), a German chemist who, in 1935, developed a simple process for determining trace (ppm) amounts of water in just about any material. Other methods include measurement of weight loss on drying, and distillation (these are not especially accurate methods), infrared/ near infrared (IR/NIR) spectroscopy, head-space gas chromatography, microwave absorption/ microwave attenuation, use of capacitive sensors. |
3rd | ANATOMY: | Three types of glands secrete substances directly onto fingerprints: the eccrine, apocrine, and sebaceous glands. Eccrine glands secrete mainly water-soluble, inorganic salts and organic substances such as amino acids, and sugars; Apocrine glands secrete both water-soluble substances such as salts and proteins, and water-insoluble organic compounds such as cholesterol; Sebaceous glands secrete almost entirely fatty (water-hating) substances such as fatty acids, glycerides, and hydrocarbons. |
NOVEMBER 2019 | ||
30th | CRIME SCENE: | CONTAMINATION of a crime scene means that something has been added into the scene at a time other than when the crime took place. Contamination of a scene can be accidental, deliberate, or a consequence of necessary actions. ACCIDENTAL: a police officer initially attending a scene of crime could unknowingly (and accidentally) damage footwear marks (deposited by the perpetrator) on the floor whilst walking through the scene to assess it. DELIBERATE: the perpetrator of the crime could deliberately contaminate a scene in setting it alight (causing arson) in the hope of destroying all traces of evidence. CONSEQUENTIAL: an arson scene will become contaminated by the actions of the fire services in bringing the fire under control. |
29th | EVIDENCE: | There are three levels of physical detail available in fingerprints. These are known as the Galton Levels (named after Francis Galton, FRS). Galton Level 1 refers to the general pattern type (e.g., arch, loop, whorl). Galton Level 2 refers to the presence of fingerprint ridge features (e.g., ridge endings, ridge bifurcations - where ridges join or split). Galton Level 3 refers to the shapes of sweat pores and the fingerpint ridges within which the pores occur. Damage features such as cuts can be thought of as additional Galton Level 2 detail. |
28th | CHEMISTRY: | Many substances will FLUORESCE, that is, emit light as a "slow glow" when they are illuminated with a sufficiently intense (energetic) source of UV light. In the process of FLUORESCENCE, light energy is first "put into" the molecule which will eventually fluoresce (scientists say light energy is "ABSORBED" by the molecule). The energy that has been received is then "redistributed" inside the molecule (scientists say that the molecule becomes "EXCITED" - because it is now at a higher energy). Finally, the molecule "gives out" some of this "extra" energy as light (scientists say the energy is "EMITTED" by the molecule - at a lower energy - and higher wavelength), and this light is observed as a relatively long-lasting visible "glow". The process of FLUORESCENCE can be exploited, for example, in the examination of blood spatter after the blood has been treated with Luminol - a molecule which "glows in the dark" when it is illuminated with UV light. |
27th | CHEMISTRY: | Light in the ULTRA VIOLET (UV) region of the electromagnetic spectrum is often used to illuminate non-visible crime scene stains so that they fluoresce (give out visible light) and become visible. Although UV LIGHT is light having wavelengths in the region 10 nano metres (nm) to 400 nm, UV-emitting lamps used to illuminate crime scenes usually operate in the "near" (300-400 nm) UV wavelength range with the most intense emission occuring at 365 nm. |
26th | CRIME SCENE: | LEGITIMATE ACCESS in the context of a crime scene is the term given to describe the fact that a person has lawful and reasonable reason to have access to a property or place. A householder, for example, has legitimate access to his or her own home; a student has legitimate access to enter the college where they study; a secretary has legitimate access to the office where she or he works. It is important to consider the matter of legitimate access when interpreting forensic evidence. For example, it would be reasonable to expect trace evidence (such as hairs, fibres, and dna) to be present at a crime scene that was shed by an innocent person who had legitimate access to the scene of crime. |
23rd | ANALYSIS: | GRIM - GLASS REFRACTIVE INDEX MEASUREMENT. GRIM is used to show whether a questioned sample of glass, such as a fragment recovered from the garment of a suspect, has the same RI as a sample of glass recovered from a scene of crime. The apparatus used to measure IR for glass, GRIM3, is available from Foster and Freeman. |
22nd | ANALYSIS: | ESDA - ELECTROSTATIC DETECTION APPARATUS. An ESDA is typically used to reveal indented handwriting in documents. Such indented writing would probably be present on a sheet of paper which lay beneath another sheet of paper on which a person wrote, say, a threatening note with a ball point pen. An ESDA is also known as an electrostatic vacuum box. |
21st | FORENSIC TERM | When a forensic scientist uses the word INDIVIDUALISATION, they mean the fact of unambiguously and uniquely connecting a single person or a single object to a crime scene. This could be achieved through the recovery of a fingerprint at a crime scene that could only have been placed at the scene at the time the crime took place; for example, a bloody fingerpint at the point of entry found at the scene. |
20th | EVIDENCE: | The first major text on the subject of fingerprints and their application in identifying people with the purpose of solving crime was "Finger Prints" written by Francis Galton FRS, published in 1892. Galton was a cousin of Charles Darwin. The full text is available HERE. Source: galton.org/ |
19th | CRIME SCENE: | ESLA is an acronym meaning ELECTROSTATIC LIFTING APPARATUS. An ESLA is typically used to lift footwear marks made in dust from smooth surfaces such as floors and doors. An ESLA is also known as an electrostatic dust print lifter. |
16th | DEFINITION: | PALYNOLOGY is the study of pollen, the grains of dust which contain the microgametophytes (which produce the male plant sperm) of seed-bearing plants. Although mainly spherical, pollen grains are distinctive to the type of plant from which they originate, and can occur with a variety of surface textures and shapes, and sizes in the range 5 to 100 microns (1 micron is 1 thousandth of a metre). Around half a million plants are thought to produce pollen. FORENSIC PALYNOLOGY is the study of pollen grains (typically recovered from the clothes or hair of a suspect) with the purpose of identifying their orgin and to show whether (or not) that suspect can be placed at the scene of crime (and origin of the pollen grains). Links to more about Palynology. |
15th | EVIDENCE: | CINDERELLA ANALYSIS is the name given to the forensic examination of shoes and other footwear to "match" them to a suspect. It is used to show pressure marks on the inner sole of the shoes, which arise as a result of the way they walk (their footfall and gait), the shape of their feet (points of pressure), and their weight distribution. Cinderella analysis is therefore "wear pattern analysis" of the inside of footwear, and can show whether or not a person has regularly worn a particular pair of shoes. Whether or not Cinderella analysis is a statistical "science" and therefore "reliable" is another question entirely. |
14th | EVIDENCE: | Glass is a frequently encountered form of physical evidence. PICK-OUT glass is the name given to the relatively large pieces of glass that are "picked out" from a window frame by a person who attempts entry to a property during forced entry and burglary. Pick-out glass is typically discarded by a burglar near to the point of entry and may contain valuable evidence such as fingerprints or blood, or perhaps footwear marks. |
13th | QUOTATIONS: | As Holmes would have it, “There is nothing more deceptive than an obvious fact.” |
12th | EVIDENCE: | Glass fragments are a common form of physical evidence. BACK-SCATTERED glass is the name given to those very small, dust-like fragments of glass that are generated when a window is broken and which "fly" back, away from the direction of impact. These are the fragments of glass that can be recovered from the hair and garments of a person who has broken a window to gain entry to, and burgle, a property, and which can show that a person was recently involved in breaking a window. |
9th | LABORATORY: | The Forensic Science Service Laboratories (previously an executive agency of the Home office opened in 1991), were formally closed in March 2012 by the Tory Government under the Leadership of David Cameron. The reason for closure, announced in December 2010, was justified on financial gounds. The closure led to more than 1000 of the world's best forensic scientists needing to find jobs. |
8th | CHEMISTRY: | A PRESUMPTIVE TEST is a preliminary chemical test (also called a spot test) used to evaluate whether or not an unknown substance is what it is thought to be. For example, a white powder is presumed to contain cocaine if a blue precipitate is formed in the first step of the SCOTT test (there are actually three stages to the SCOTT test). Chemical ANALYSIS will be needed to confirm the presumptive test. Because presumptive tests involve a colour change, they have also been called colorimetric tests. |
7th | EVIDENCE: | Evidence that has CLASS CHARACTERISTICS belongs to a group. A fibre that originated in a mass produced garment would have class characteristics because it will be indistinguishable from any other fibre (recovered for analysis) from any of those mass produced garments. Similarly, the sole pattern on a pair of brand new training shoes would be indistinguishable from those on any other training shoes of the same brand and size, so footwear marks made by those shoes would all exhibit the same class characteristics, and be indistinguishable from one another. |
6th | EVIDENCE: | Physical evidence that has INDIVIDUAL CHARACTERISTICS is unique. A fingerprint is said to have individual characteristics because it can be used to uniquely identify a person. Other examples could include a paint chip from a re-painted vehicle (because the outer paint layers are individual to that vehicle) and an old, worn tool such as a jemmy or screwdriver used say, to force entry into a property (because damage on the tip of the tool could leave a unique impression on the window frame). |
5th | DEFINITION: | BIOMETRICS is the process or technology of measuring the dimensions of anatomical / physiological features, such as in facial recognition, fingerprint examination, and signature analysis. |
2nd | LAW: | The first known case allowing a questioned document examiner’s testimony was that of Revett v Braham, 100 Eng. Rep. 1139 (KB 1792). 100 Eng. Rep. 1139: English Report, Volume 100, Article 1139; KB 1792: King's Bench in the Year 1792. The case was heard on Tuesday 24th January 1792 and is entitled " GOODTITLE ON THE DEMISE OF REVETT against BRAHAM " in the English Report. |
1st | ANALYSIS: | IRMS - Isotope Ratio Mass Spectrometry - can be used to distinguish between chemically identical substances from different sources. |
OCTOBER 2019 | ||
31st | DEFINITION: | Are ears unique? EAROLOGY is the study of the shape of the outer ear (pinna). Alfred Iannarelli (in 1989; and author of Ear Identification) examined over 10,000 ears and found that they all were different. |
30th | ANATOMY: | Skin is the largest organ of the human body (~15% of body mass). An adult typically sheds at least 350 million dead cells (~4.5 grams) every day. |
29th | DEFINITION: | Serology is the scientific study of blood serum and other bodily fluids, and in particular, the diagnostic identification of antibodies in the serum. Red blood cells (erythrocytes) make up around 45% of the blood volume in humans, and are responsible for carrying oxygen around our bodies. |
26th | PEOPLE: | The first person to observe DNA was the German biochemist Frederich Miescher (in or around 1870) when isolating its component nucleic acids. |
25th | EVIDENCE: | There are 4 fingerprint pattern classifications: ARCH; LOOP; WHORL; UNCLASSIFIED. |
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