FINGERPRINTS
The Skin
The human skin is composed of numerous layers: the epidermis on top, followed by the papillae, and then the dermis. The form and pattern of ridges on the surface of the skin is determined by the dermal papillae. These ridges, known as minutiae, are formed pre-birth, and stay with the individual throughout their life. Each skin ridge holds a row of pores through which sweat is released. It is a combination of these ridges and the sweat that causes a fingerprint to be left behind when the finger comes into contact with a surface.
Fingerprints
Fingerprints can be visible, plastic or latent. Visible prints are left in a substance such as paint or blood, clearly visible. Plastic prints are left in some kind of soft surface, such as putty or wet paint, and are also visible. However latent prints are left in bodily oils, and may require treatment to be visualised. Fingerprints are reproductions of the friction ridge skin on the palmar surface of the hands. By the same definition, footprints are reproduction of the friction ridge skin on the soles of the feet. Generally, no records of footprints are kept on file at police departments or the FBI. This is so because people do not generally commit crimes using their feet. However, footprints will be collected at a crime scene when necessary. With that in mind, there are three types of fingerprints: latent fingerprints (invisible to the naked eye -- think of when you see a CSI on tv using powder on a surface. They are developing latent fingerprints); patent (visible to the eye -- think of a bloody fingerprint); or known fingerprints -- these are a set of fingerprints that are known to belong to a specific person such as the fingerprint card collected at the time of arrest, known as a ten-print card.) These known fingerprints will be compared to the latent or patent fingerprints recovered from crime scenes. This procedure is called fingerprint comparison and are done by Latent Print Examiners (LPE).
Fingerprint Patterns
The fingerprints left behind, which are unique to an individual, are composed of a collection of loops, whorls and arches. Loops are characterised by ridge lines that enter from one side of the pattern, curve around, and exit from the same side. Whorls are divided into four types; plain, central pocket whorl, double whorl, and accidental. Arches are characterised by ridge lines that enter the print from one side and exit the other side. There are four basic bifurcations (divides) in fingerprints; where a ridge divides, where a ridge ends, a lake, and an independent ridge.
Arches occur in about 5% of the encountered fingerprints. The ridges of the finger run continuously from one side of the finger to the other and make no backward turn. Normally, there is no delta in an arch pattern but if it exists, there must be no re-curving ridge that intervenes between the core and delta points.
Loops are seen in almost 60 to 70% of the fingerprints that are encountered. The ridges make a backward turn in loops but they do not twist. This backward turn or loop is distinguished by how the loop flows on the hand and not by how the loop flows on the card where the imprint is taken. This imprint on the fingerprint is similar to the reverse image that we see when we look at ourselves in the mirror. A loop pattern has only one delta.
Whorls can be found in about 25 to 35% of the fingerprints that are encountered. Some of the ridges in a whorl make a turn through at least one circuit. Therefore any pattern that contains two or more deltas will be a whorl.
Subcategories of these patterns. There are two sub-types of arch patterns
The plain arch pattern a consistency of flow can be observed. It starts on one side of the finger and the ridge then slightly cascades upward. This almost resembles a wave out on the ocean and then the arch continues its journey along the finger to the other side. The plain arch pattern is the simplest of the fingerprints to discern.
The Tented arch similarity between this pattern and the plain arch is that it starts on one side of the finger and flows out to the other side in a similar pattern. However, the difference is that the tented arch lies in the ridges in the centre and is not continuous like the plain arch. They have significant up thrusts in the ridges near the middle that arrange themselves on both sides of an axis. The adjoining ridges converge towards this axis and thus appear to form tents.
There are three sub-categories of loops
Radial loops are named after a bone in the forearm known as radius that joins the hand on the same side as the thumb. The flow of these loops runs in the direction of the radius bone i.e. the downward slope of the radial loop is from the little finger towards the thumb of the hand. These loops are not very common and most of the times will be found on the index fingers.
Ulnar loops are named after a bone in the forearm called ulna. This bone is on the same side as the little finger and the flow of this pattern runs from the thumb towards the little finger of the hand.
Double loop pattern consists of two distinct and separate loop formations. It has two distinct and separate shoulders for each core, two deltas and one or more ridges that make a complete circuit. There is at least one re-curving ridge within the inner pattern area between the two loop formations that gets touched or cut when an imaginary line is drawn.
There are three sub-groups of whorls
In the Plain whorl ridges in these whorls make a turn of one complete circuit with two deltas and are therefore circular or spiral in shape. This is the simplest form of whorl and also the most common.
Central pocket loop whorl consist of at least one re-curving ridge or an obstruction at right angles to the line of flow with two deltas and if an imaginary line is drawn in between then no re-curving ridge within the pattern area will be touched or cut. These whorl ridges make one complete circuit and may be oval, circular, spiral or any variant of a circle.
The Accidental whorl composition of the pattern in accidental whorl is derived from two distinct types of patterns that have at least two deltas. Therefore whorls containing ridges that match the characteristics of a particular whorl sub-grouping are referred to as accidental whorls.
Enhancing Prints
It is necessary to treat latent prints in order to enhance them for collection and comparison. Many forms of print enhancement are based on the fact that latent prints contain numerous different compounds that will react to certain tests. The method used will often depend on the surface onto which the print has been left, and the environment and circumstances. Prints on a non-absorbent surface, such as glass, are usually enhanced using powders or superglue fuming. However prints on soft and porous surfaces, such as cloth, may require some kind of chemical treatment.
The application of aluminium powder is the most common method of developing latent prints. The fine powder is applied with a brush, after which it adheres to perspiration residues and body oil deposits, visualising the print. The Magna Brush can be used to apply magnetic-sensitive powder. As the brush has no bristles, the chances of the print being damaged are greatly reduced. Ninhydrin, or triketohydrindene hydrate, is a compound that reacts with the amino acids in the print to produce a purple colouring. This technique is particularly useful on porous surfaces such as paper, though is not useful on wetted items or silk finish surfaces.
The iodine fuming method uses iodine crystals that vaporise by sublimation when heated. These vapours combine with components on the latent print, making it visible. The print developed will eventually fade, so should be photographed immediately once observable. The superglue fuming method used ethyl or methyl cyanoacrylate which, when fumed, produces a white deposit on the latent print. The superglue is placed in an enclosed chamber with the item and heated, causing the superglue to adhere to the print. When lifting an enhanced print, tape should be applied to the entire print and pressure applied before being carefully lifted. The lift should be smooth and without pauses.
For more on Personal Injury Law.
The human skin is composed of numerous layers: the epidermis on top, followed by the papillae, and then the dermis. The form and pattern of ridges on the surface of the skin is determined by the dermal papillae. These ridges, known as minutiae, are formed pre-birth, and stay with the individual throughout their life. Each skin ridge holds a row of pores through which sweat is released. It is a combination of these ridges and the sweat that causes a fingerprint to be left behind when the finger comes into contact with a surface.
Fingerprints
Fingerprints can be visible, plastic or latent. Visible prints are left in a substance such as paint or blood, clearly visible. Plastic prints are left in some kind of soft surface, such as putty or wet paint, and are also visible. However latent prints are left in bodily oils, and may require treatment to be visualised. Fingerprints are reproductions of the friction ridge skin on the palmar surface of the hands. By the same definition, footprints are reproduction of the friction ridge skin on the soles of the feet. Generally, no records of footprints are kept on file at police departments or the FBI. This is so because people do not generally commit crimes using their feet. However, footprints will be collected at a crime scene when necessary. With that in mind, there are three types of fingerprints: latent fingerprints (invisible to the naked eye -- think of when you see a CSI on tv using powder on a surface. They are developing latent fingerprints); patent (visible to the eye -- think of a bloody fingerprint); or known fingerprints -- these are a set of fingerprints that are known to belong to a specific person such as the fingerprint card collected at the time of arrest, known as a ten-print card.) These known fingerprints will be compared to the latent or patent fingerprints recovered from crime scenes. This procedure is called fingerprint comparison and are done by Latent Print Examiners (LPE).
Fingerprint Patterns
The fingerprints left behind, which are unique to an individual, are composed of a collection of loops, whorls and arches. Loops are characterised by ridge lines that enter from one side of the pattern, curve around, and exit from the same side. Whorls are divided into four types; plain, central pocket whorl, double whorl, and accidental. Arches are characterised by ridge lines that enter the print from one side and exit the other side. There are four basic bifurcations (divides) in fingerprints; where a ridge divides, where a ridge ends, a lake, and an independent ridge.
Arches occur in about 5% of the encountered fingerprints. The ridges of the finger run continuously from one side of the finger to the other and make no backward turn. Normally, there is no delta in an arch pattern but if it exists, there must be no re-curving ridge that intervenes between the core and delta points.
Loops are seen in almost 60 to 70% of the fingerprints that are encountered. The ridges make a backward turn in loops but they do not twist. This backward turn or loop is distinguished by how the loop flows on the hand and not by how the loop flows on the card where the imprint is taken. This imprint on the fingerprint is similar to the reverse image that we see when we look at ourselves in the mirror. A loop pattern has only one delta.
Whorls can be found in about 25 to 35% of the fingerprints that are encountered. Some of the ridges in a whorl make a turn through at least one circuit. Therefore any pattern that contains two or more deltas will be a whorl.
Subcategories of these patterns. There are two sub-types of arch patterns
The plain arch pattern a consistency of flow can be observed. It starts on one side of the finger and the ridge then slightly cascades upward. This almost resembles a wave out on the ocean and then the arch continues its journey along the finger to the other side. The plain arch pattern is the simplest of the fingerprints to discern.
The Tented arch similarity between this pattern and the plain arch is that it starts on one side of the finger and flows out to the other side in a similar pattern. However, the difference is that the tented arch lies in the ridges in the centre and is not continuous like the plain arch. They have significant up thrusts in the ridges near the middle that arrange themselves on both sides of an axis. The adjoining ridges converge towards this axis and thus appear to form tents.
There are three sub-categories of loops
Radial loops are named after a bone in the forearm known as radius that joins the hand on the same side as the thumb. The flow of these loops runs in the direction of the radius bone i.e. the downward slope of the radial loop is from the little finger towards the thumb of the hand. These loops are not very common and most of the times will be found on the index fingers.
Ulnar loops are named after a bone in the forearm called ulna. This bone is on the same side as the little finger and the flow of this pattern runs from the thumb towards the little finger of the hand.
Double loop pattern consists of two distinct and separate loop formations. It has two distinct and separate shoulders for each core, two deltas and one or more ridges that make a complete circuit. There is at least one re-curving ridge within the inner pattern area between the two loop formations that gets touched or cut when an imaginary line is drawn.
There are three sub-groups of whorls
In the Plain whorl ridges in these whorls make a turn of one complete circuit with two deltas and are therefore circular or spiral in shape. This is the simplest form of whorl and also the most common.
Central pocket loop whorl consist of at least one re-curving ridge or an obstruction at right angles to the line of flow with two deltas and if an imaginary line is drawn in between then no re-curving ridge within the pattern area will be touched or cut. These whorl ridges make one complete circuit and may be oval, circular, spiral or any variant of a circle.
The Accidental whorl composition of the pattern in accidental whorl is derived from two distinct types of patterns that have at least two deltas. Therefore whorls containing ridges that match the characteristics of a particular whorl sub-grouping are referred to as accidental whorls.
Enhancing Prints
It is necessary to treat latent prints in order to enhance them for collection and comparison. Many forms of print enhancement are based on the fact that latent prints contain numerous different compounds that will react to certain tests. The method used will often depend on the surface onto which the print has been left, and the environment and circumstances. Prints on a non-absorbent surface, such as glass, are usually enhanced using powders or superglue fuming. However prints on soft and porous surfaces, such as cloth, may require some kind of chemical treatment.
The application of aluminium powder is the most common method of developing latent prints. The fine powder is applied with a brush, after which it adheres to perspiration residues and body oil deposits, visualising the print. The Magna Brush can be used to apply magnetic-sensitive powder. As the brush has no bristles, the chances of the print being damaged are greatly reduced. Ninhydrin, or triketohydrindene hydrate, is a compound that reacts with the amino acids in the print to produce a purple colouring. This technique is particularly useful on porous surfaces such as paper, though is not useful on wetted items or silk finish surfaces.
The iodine fuming method uses iodine crystals that vaporise by sublimation when heated. These vapours combine with components on the latent print, making it visible. The print developed will eventually fade, so should be photographed immediately once observable. The superglue fuming method used ethyl or methyl cyanoacrylate which, when fumed, produces a white deposit on the latent print. The superglue is placed in an enclosed chamber with the item and heated, causing the superglue to adhere to the print. When lifting an enhanced print, tape should be applied to the entire print and pressure applied before being carefully lifted. The lift should be smooth and without pauses.
For more on Personal Injury Law.