Sherlock, St Louis & Co. The Under of Investigation - Cathie Louvet's Chronicle - DNA



Cathie Louvet's chronicle


 Sherlock, St Louis & Co. The Under of Investigation - Cathie Louvet's Chronicle - DNA
 Sherlock, St Louis & Co. The Under of Investigation - Cathie Louvet's Chronicle - DNA
 Sherlock, St Louis & Co. The Under of Investigation - Cathie Louvet's Chronicle - DNA
 Sherlock, St Louis & Co. The Under of Investigation - Cathie Louvet's Chronicle - DNA
Folder n°10 : fingerprints

1. A little history:

Before the 19th century:
It was at an archeological site in northwestern China, dating back 6000 years, that the first fingerprints were discovered, impressions of papillary ridges (which have papillae, conical projections formed near the surface of the skin), without knowing whether they were left intentionally or accidentally. Sixty-five-year-old Babylonian pottery has also been discovered, probably serving as a signature.
However, the first recorded example of the use of fingerprints as a means of identification dates back to the Chinese Qin dynasty, between 221 and 206 BCE. The documents found were sealed with clay in which the imprint and the name of the author were printed. But it is from 105 AD, after the invention and the use of paper by the Chinese, that the digital signature becomes more common.
However, the Chinese are not the only ones to resort to this process of identification. Indeed, in Japan, in 702 AD, a domestic law states that "In the case of a husband who does not know how to write, let him employ another man to write the document in his place, and after his name of husband he will sign with his own index. " Thus, in past centuries, the affixing of the fingerprint was mainly used to formalize documents of everyday life.
19th century:
But it was not until the 19th century that other properties were discovered. In 1823, the Czech physiologist Jan Evangelista Purkinje published a thesis titled Physiological Examination of the Organ Organ and the Cutaneous System, in which he classified the fingerprint drawings into nine groups.
William James Herschel, English British Indian officer born in 1833 in Slough and died in 1917, grandson of William Herschel and son of John Herschel, both astronomers, is known to be the first to have used fingerprints for Identification. Ben Herschel, an officer in Bengal at the registry office, studied his own fingerprints and those of others. He realized that the marks left by the fingers and hands were unique to each individual. He decided, around 1850, to use them in his work, especially against fraud and as a signature on contracts. In 1858, he perfected his system by raising the palmar imprint in its entirety. Rajyadhar Konai, a local businessman, is one of the first people to identify with this process. In 1877, William Herschel sent a letter to the Inspector General of Bengal Prisons in which he suggested that the system of fingerprint identification be extended to other areas under the influence of the British.


Henry Faulds, physician and Scottish missionary born in 1843 and died in 1930, appointed by the Presbyterian Church to establish a medical mission in Japan, leaves England with his young wife in 1873. A few years later, while accompanying an archaeologist friend Edward S. Morse at the site of his excavations, he notices fingerprints on pottery. By examining his own fingers and those around him, he deduces that the "drawings" are specific to each individual. With the intention of promoting the system of identifying individuals by their fingerprints, Faulds sends a letter to Charles Darwin who, aged and ill, transmits it to his cousin Francis Galton, anthropologist, explorer, geographer, psychometrist and statistician, father of Eugenism and Comparative Psychology. Francis Galton sent the letter to the Anthropological Society of London, which did not take it seriously. It was not until 1880, following the publication in the journal Nature of an article by Faulds in which he demonstrated the interest of using printing ink to record fingerprints in order to confuse criminals, that Galton was really interested in it.
Francis Galton resumed Faulds' research for his own account and, after giving a lecture to the Royal Society on the Bertillon method and the study of dermatoglyphs (scholarly name for fingerprints), he published in 1892 a book entitled Finger Prints, in which he establishes the uniqueness of the digital drawings (specific to each finger, therefore to each individual) and their permanence (the prints do not change during a lifetime). It is through his work that fingerprints will be used officially as a means of identification.
After studying Galton's writings, Argentine police officer Juan Vucetich created the first fingerprint file in 1891. The following year, he will be the first in the history of modern police to identify the author of an infanticide, Francisca Rojas, with his fingerprints.

Two years later, in 1893, Sir Edward Henry, British inspector assigned to Bengal, developed an identification system similar to that of Vucetich, consisting of defining families of papillary drawings: buckles, arches, vortices, system still used in English-speaking countries. Back in England, Henry had his system adopted by Scotland Yard in 1897. In 1901, he created a file of fingerprints, which completes the "bertillonnage".
Bertillon, employed at the Prefecture de Police in Paris, is at first refractory to this system which directly competes with his own invention, anthropometry. But quickly, he understands the importance of this identification process. In 1896, he decided to fingerprint the right hand of all convicts while retaining his method of anthropometric classification. In 1902, managing to confuse the criminal Henri Léon Scheffer from his fingerprints taken at the scene, he formalized the use of this process by creating a systematic file.


2. A unique fingerprint:
Dermatoglyphs, or fingerprints, are the traces that we leave behind each time we touch an object. The patterns drawn by the ridges and folds of the skin are different for each of us. From the thumb to the little finger, the patterns are not the same, which is why a good reading should include the ten fingers. The identical twins have different imprints, even if at first glance they are similar. Only a detailed search can distinguish the nuances.
It is estimated that fingerprints begin to form in utero between the 10th and 16th weeks of fetal life, by folded cell layers. The convolutions of the ridges giving them their characteristic pattern depend on many factors: the speed of growth of the fingers, the feeding of the fetus, its blood pressure among others. The digital plots consist of ridges separated by valleys called "furrows".

Our skin is covered with a little greasy film, and the ridges drawn on our fingers are dotted with small holes called pores through which the sweat which forms small deposits of salt flows. As we do not wash our hands constantly, these deposits are mixed with all sorts of products or particles (dirt, various fats, dead skin), forming a kind of "paste" that we leave in a very thin layer on objects that we touch.
There are two kinds of fingerprints: the direct imprint, which leaves a visible mark, and the latent imprint, dirt, sweat or other residue deposited on an object or surface. These footprints are divided into three main categories: the arch, the vortex and the loop, themselves subdivided by a very large number of elements, including forks, islands, spaces, giving a unique character to the latent imprints .

3. Révélations:
In order to reveal the invisible footprints to the naked eye, the laboratories have a whole arsenal of chemical revelation based on the same principle: the revealing product clings to the components of the trace.
Light impressions: for porous surfaces (paper, cardboard, kraft), the room is first immersed in a chemical solution called DFO (deferoxamine), then it is placed in an oven for drying. At this point, we can not see anything. Indeed, it is necessary to illuminate the imprint with a special light and wear appropriate glasses: the trace appears as "illuminated"!
Well-stamped footprints: Ninhydrin can also reveal impressions left on paper or cardboard. Unlike DFO, ninhydrin reacts with the amino acids (molecules essential to life) contained in the impression. But the principle remains the same: we quench, we dry and we look. Although the reaction is longer, from a few hours to weeks depending on the age of the trace, the quality of the impression that appears is much better.
Glued footprints: on complex surfaces such as a bicycle, we use the technique called "fumigation" or "cyano-acrylate" which consists of heating Superglue until it vaporizes to deposit on the components of the impression. A nice white trace appears. In the case of a white surface, a dye is applied. This very practical technique should be used with great care because the vapors of Superglue are highly toxic.
Latex footprints: Many criminals abandon their latex gloves on a crime scene thinking they are safe. And they are wrong !! Although the latex is neither a smooth nor porous material, it is still possible to reveal the imprints found there thanks to RTX (ruthenium tetroxide) which is vaporized in a hermetically sealed enclosure and under a hood , its vapors being very toxic.
Golden fingerprints in fine gold: in order to reveal the most tenuous prints, the piece is fixed in a large metal box where the void is created as soon as it is closed. A vacuum so strong that the metals (gold and zinc) placed inside in small cups will turn into gas that will be deposited in the furrows footprints, making them visible. This technique works on any medium provided it is not too bulky or too full of vacuum, such as expanded polystyrene.

4. How to read a fingerprint:
Contrary to what we see in movies or TV series, it is not enough to superimpose two prints to identify the owner. Because, in reality, the two traces never completely coincide. On one side, there is the trace on the stage, often partial or thick; on the other hand, we have the reference fingerprint that has been taken carefully with the desired amount of ink and ideally roll the fingertip associated with a name and stored in a file. The delicate task of identification is to find the commonalities between the two prints.
Grossie strongly, a footprint has a number of details called "minutiae", for example bifurcation, line stops, hooks, bridges, dead ends, lakes, etc ... The work of the examiners, real work of ant, requires a lot of concentration and meticulousness !!
Fortunately, the use of computers is a real plus. We pass the image of the imprint in a special software that will bring out a constellation of small colored symbols indicating the location and the direction of the minutiae. But the human eye remains necessary: ​​indeed, if the footprint is scarred by a scar, the computer will take its fork with the ridges for line stops. It must therefore be indicated that this is not the case. Next, the computer compares the myriad of colored dots in the suspect fingerprint with those of the reference fingerprint, classified in FAED (an automated fingerprint file listing the fingerprints of over two million people, all involved in a criminal case but not necessarily guilty). The computer renders a list of cards that could match. It is up to an operator to perform a manual comparison in order to validate those that match. For added security, a second operator will have to confirm this identification. In France, a minimum of twelve points of concordance is required to affirm that they are the same person.

5. Attention to errors:
However, caution must be exercised before determining that a fingerprint belongs to a specific person, as the following case demonstrates. The American Brandon Mayfield was accused, in March 2004, of having participated in the attacks that bloodied the Spanish capital, after they found on the spot a bag of explosives with his imprints on it. More exactly, the US police had identified the fingerprints as his, while at the same time the Spanish authorities attributed the fingerprints in question to another individual. Did these two men have the same fingerprints? Certainly not! The mistake was simply a misinterpretation ...
It may happen that the quality of the trace is bad, for example because its owner had greasy fingers; in this case, the ridges are thickened and a line stop can turn into a bifurcation. A closer look would have disregarded it. However, this possibility entails the risk that the experts neglect too many points to match the X footprint with that of Mr. Z, especially if the pressure for the identification of a suspect is particularly strong!
However, the very small margin of error, barely twenty cases identified, does not mean that we must give up this very practical technique and all very reliable, but that we must continue research in order to make it even more reliable ...


Cathie Louvet