Fingerprints are impressions of patterns formed by the papillary or epidermal ridges of the fingertips. The ridge patterns of fingers appear between 12 to 16 weeks of intrauterine life and the formation is completed by 24 weeks. At birth a fine pattern of ridges is seen on the skin of the bulbs of the fingers and thumbs, parts of the palms and the soles of the feet.
Dermatoglyphics is the study of ridge patterns in the skin. This system was first used in India in 1858, by Sir William Herschel in Bengal. Sir Francis Galton systematized this method in 1892. Fingerprint Bureau was first established in Kolkata.
Classification
Loops (about 60 to 70 percent) – Radial and Ulnar
Whorls (about 25 to 35 percent) – Concentric, Spiral, Double spiral and Almond-shaped
Arches (about 6 to 7 percent) – Plain, Tented and Exceptional
Composite (about one to two percent) – Central pocket loops, Lateral pocket loops, Twinned loops, Accidentals.
In a whorl, the ridges form a series of circles or spirals around the core. In a composite, there are combinations of two or more of the types, namely arches, loops or whorls.
The final identification of fingerprints is made by comparison of many details of characteristics which occur throughout the ridge areas and by the sequence in which these characteristics occur, but not by comparing the patterns. The characteristics may take the form of ridge endings, bifurcations, lake formations, or island formations.
In practice 10 to 12 points of fine comparison are accepted as proof of identity. The patterns are not inherited and paternity cannot be proved through fingerprints patterns. The pattern is different even in identical twins. The patterns are distinctive and permanent in individuals. The fingerprints system is the only guide to identity, which is unfailing in practice. The details of these can be accurately teleprinted. Palm and foot also provide similar material.
Poroscopy
This is further study of fingerprints, described by Locard. The ridges on fingers and hands are studded with microscopic pores, formed by mouths of ducts of subepidermal sweat glands. Each millimeter of a ridge contains 9 to 18 pores. These pores number in thousands per square centimeter.
These pores are permanent and unchanged during life and vary in size, shape, width, starting and stopping on occasion and branching at points, position, extent and number over a given length of ridge in each individual. This method of examining pores is called poroscopy, and is useful when only fragments of fingerprints are available.
The Individuality of Fingerprints
The fingerprints are capable of endless variation so that it has been speculated that there is one chance in sixty-four billions of two persons having identical fingerprints.
Mode of Production
A constant stream of sweat covers the skin and when the person is excited, the output of sweat increases. Sweat contains about 99% water and 1% solids, which include salt, sulphates, carbonates, lactic acid, urea, fatty acids, formic acid, acetic acid, butyric acid and sometimes a little albumin.
It may also contain oil exuded by the sebaceous glands, which is present on the fingertips through touching the face, neck, hair, scalp, etc. If any part of finger is applied to a smooth surface, a greasy impression of its pattern is made on it.
Techniques of Fingerprinting
The hands are washed, cleaned and dried, as otherwise the output will be blurred. The fingerprints are recorded on unglazed white paper using printer’s ink.
(1) A plain stamp is taken by applying ink to the tips of the fingers and placing the fingers directly on paper.
(2) The rolled fingerprint is taken by rolling the fingers on paper from outward to inward in such a way as to obtain an impression of the whole tip.
If rigor morris is well developed, incision into the palmar surface of the fingers at the proximal interphalangeal joint will enable the fingers to be straightened, and printing can be carried out.
Types:
(1) The latent print (chance) is an invisible or barely visible impression left on a smooth surface.
(2) Visible prints are formed by. fingers stained with blood or ink or other medium.
(3) The plastic print is an impression made on a soft surface, such as soap, cheese, mud, pitch, candles, thick dried blood, adhesives, etc.
Burnt skin of the fingers on healing shows its original pattern. In manual laborers working with lime, sand, and cement the ridges on the bulbs get unduly rubbed and become broken and indistinct. Ridge impressions get malformed if the quality of ink is poor, when the ink is too liquid and spreads into the depressions, if the digit is rolled often or pulled, and when the paper is placed upon an uneven or rough surface.
Fingerprints may be taken from almost any surface with which the fingers come in contact, including certain fabrics and human skin. A latent may be developed by dusting the area with colored powders to provide a contrast, and its pattern is recorded by photography. It can also be examined by oblique lighting.
The commonly used powder is ‘grey’ powder (chalk and mercury), but white powders (lead carbonate or French chalk) are used for dusting dark surfaces. Fingerprints on paper, wood and fabrics are developed by treating them with 5% silver nitrate solution and then fixing them with sodium thiosulphate.
Fingerprints on paper can also be developed by exposing it to the vapors of iodine or osmium tetroxide. Electron auto-radiography method uses a high energy beam of X-rays to irradiate the lead dust on fingermarks. The scanning electron microscope visualizes latent fingerprints on metal and glass. Using a continuous wave argon ion laser and observing through suitable filters, latent fingerprints show luminescence. Even ten years old fingerprints can be developed.
LIFTING OF FINGERPRINTS
Fingerprints on a large immovable hard surface are developed, photographed and then adhesive surface of cellophane tape is pressed on the print, the image is taken out gently and pasted against a cardboard sheet for permanent preservation.
The fingerprints of an assailant will remain on the victim only after death. During pre-death struggle both the assailant and the victim will sweat due to nervous tension and one exudate will cancel out the other. After death, the victim will not sweat, due to which the fingerprints will be left on the body. Electronographic method is used to develop latent fingerprints on skin of living persons or dead bodies. Sweating from exertion is seen on the forehead, axilla, small of the back, etc. whereas nervous sweating is almost confined to the hands and feet.
Fingerprints in Decomposed Bodies
Ridges are present both in dermis and epidermis. In advanced putrefaction and in cases of drowning, the skin is frequently found loose like a glove, which should be removed, preserved in formalin and used for impressions. Prints can be obtained from the dermis after epidermis is lost.
Histological sections up to a depth of 0.6 mm. from the surface of the skin give satisfactory fingerprints. In dead bodies, the palmar skin of the terminal phalanx of each finger should be removed separately from both hands, and after labeling, placed in separate containers, containing 10% formalin, and sent to the fingerprint bureau, if it is not possible to take the prints.
If the fingers are shriveled, they should be immersed in 20% acetic acid for 24 to 48 hours, or air, glycerin or liquid paraffin is injected into the bulb, which will cause the shriveling to swell to normal size. If the skin is dehydrated, the finger is soaked in 3% solution of potassium hydroxide in warm water for a short period, until the fingers regain normal size.
If the skin is fragile lead carbonate mixed with paraffin is applied on the skin and X-rayed. If the fingers are sodden, wrinkled or mummified, their outline can be made level by injecting liquid paraffin, or even formalin, within the tissues of the palmar aspects of the terminal phalanx of each finger.
Persistence of Impression at Scene of Crime: Impressions may persist for years, if undisturbed by cleaning. Even outside the house, they may persist for weeks. On glazed paper they persist for more than three years.
MUTILATION OF FINGERPRINTS
Criminals sometimes attempt to mutilate the pattern by self- inflicted wounds or burns, application of corrosives or erosion against a hard surface, but they are not destroyed unless the true skin is completely destroyed. They produce additional characteristics. It leaves some part of the skin undamaged, unless skin grafts are made.
In most cases of coeliac disease, there is moderate epidermal ridge atrophy and even loss of pattern. Incomplete atrophy of the ridges is usually seen in dermatitis. Ridge alteration occurs in eczema, acanthosis nigricans, scleroderma, and dry or atrophic skin. Permanent impairment of the fingerprint pattern occurs in leprosy, electric injury and after exposure to radiation.
In infantile paralysis, rickets and acromegaly, though the pattern is not altered, the distance between the ridges can be changed. Fingerprints are better protected than other parts of the body, e.g. in case of burns they are bent inwards against the palm of the hand.
Computerization
Fingerprint reader (FINDER) is a computerized automatic fingerprints reading system which can record each fingerprint data in half second. Prints of eight fingers are recorded excluding little fingers. The light reflected from a fingerprint can be measured and converted to digital data which is classified, codified and stored in the computer.
Medicolegal Importance
(1) The recognition of impressions left at a scene of crime, e.g., on weapons, furniture, doors, utensils, clothes, etc., establish the identity of the criminal.
(2) The identification of suicides, deserters, persons suffering from loss of memory or those dead or unconscious after being involved in an accident and of decomposing bodies.
(3) Identification in case of accidental exchange of newborn infants.
(4) The prevention of impersonation.
(5) To maintain identity records.
(6) Cheques, bank notes and other legal documents can bear a fingerprint.
In criminals, impressions of all the ten fingers are taken, but for civil purposes, the left thumb impression only is taken.
FOOTPRINTS (Podogram)
The skin patterns of toes and heels are as distinct and permanent as those of the fingerprints of fingers. Footprints of newborn infants are used in some maternity hospitals to prevent exchange or substitution of infants. A fresh footprint of suspected person is taken and compared with the original.
Any peculiarities in the foot, such as a flat foot, supernumerary toes, scars or callosities are likely to be found in the footprint. In case of boot mark the pattern and arrangement of nails or holes in the sole may be useful. A footprint produced by walking is usually larger than one produced by standing. The imprint on soft and loose material like sand is smaller than the foot, and the imprint produced on mud or clay is larger.
A foot mark expert may identify a shoe with a mark made at the scene of crime, and by general examination may find out the number of persons involved, their actual movements at the scene and their point of entry. Individual impressions, especially in yielding soil, will indicate the shoe size and approximate weight of the person and any peculiarity of gait.
A partial foot mark may be quite sufficient to positively identify a shoe. Footmarks are recorded by photography, casts or lifting or by a combination. Casts can only be taken when there is a foot mark in depth. As they are three dimensional, they can be easily compared with the suspect’s shoes even by lay persons. Crime scene footprints are compared with the comparison prints made on similar surface by the suspect.
They are taken in normal standing position, standing position with pressure on inner side and outer side, when walking and when jumping. It may be possible to know whether the track marks are that of a young or old person. Step length of an adult woman is 45 to 55 cm. and that of an adult male 63 to 70 cm.
PALATOPRINTS
In the anterior part of the palate, the structural details like the rugae are individual specific and permanent. The palatoprints can be used in the same way as fingerprints.
LIPPRINTS (Cheiloscopy)
They are useful in personal identification. Lip prints are divided into eight patterns which are specific to the individual; vertical, branched, intersected, reticular patterns, etc. Minor differences can be noted between the right and the left and upper and lower lips.
EAR PRINTS
Ears have four basic shapes: oval, round, rectangular and triangular. The shapes of ear lobes and the tips of ears are of various types. Most of the ear prints are found on doors or windows. From the suspect three prints are taken
(1) functional pressure
(2) gentle pressure
(3) more pressure on a glass pane.
It is made visible as in the case of fingerprints and a photograph of the print is taken.
The same process is applied to the ear prints from the scene. Photocopies of both known and unknown ear prints are produced on plain and transparency overlays. The transparency overlay is put on the top of the unknown print and taped to the top of a light box.
If the tragus point, crus of the helix points and antitragus point fit, look at the lower and upper crura of the antihelix and the helix rim. If all details coincide the prints are from the same source. The opinion can be positive, highly probable, probable, possible or no basis for comparison.
NOSE PRINTS
The lines on the nose and the shape of the tip are helpful in identification.
