Since the rise of forensic science , fingerprints have become well known to the general public as a method of identifying people. Anyone knows that you have to wear gloves for any crime to be committed, otherwise you will be caught very quickly. But deep down, who knows how they are formed and why? We now explain how fingerprints are formed and how they can be recovered.
How are fingerprints formed and how can they be recovered?
The human body has several areas where there are papillary ridges (a kind of raised grooves): the palms of the hands, the fingers and the soles of the feet . When raised, they can leave marks on the supports. We speak then of traces or tracks , two terms that do not have the same meaning for forensic scientists.
The trace is the mark, visible or invisible, left by the papillary ridges on a support. When an offender manipulates an object at the scene of a misdemeanor or crime, they can leave a trace of their fingerprints (fingers) or also of the prints left by the palms of the hand.
The imprint itself is the result of the complete fixation of the papillary ridges after inking them. The fingerprints of a suspect are taken during the marking operations carried out at the police premises.
What are the characteristics of fingerprints?
Papillary ridges are not unique to humans . Other species also have this particularity, such as koalas and orangutans.
In summary, papillary ridges are located in the epidermis, the outer layer of the skin. They are actually the exact projection of the designs present in depth, on the dermis. The ridges are surrounded by papillae (hence the name “papillae”), themselves connected to nerve endings that give us the sense of touch . Between the ridges are the grooves (holes). This alternation of ridges and grooves forms the papillary designs. In the center of the ridges we can distinguish black points that correspond to pores . Without them, there would be no evacuation of perspiration.
Papillary ridges have three main characteristics:
- They are individual and unique . Even identical twins have different fingerprints.
- They are immutable . They do not change from their formation during intrauterine life to their destruction during the putrefaction of the body.
- They are unchangeable. As they originate in the deep layers of the dermis, they can be reconstituted after superficial destruction of the epidermis. But with a burn or other deeper destruction, the papillary ridges can be damaged or even destroyed.
How are fingerprints formed?
The hands and feet are formed from the fifth and sixth weeks of pregnancy. Pads appear on the palms of the hands and the tips of the fingers. Then the papillary lines form in the dermis around the 10th week as a proliferation of cells. At approximately week 16, the dermis development phase is complete and the digital drawing is fully visible on the surface of the skin .
The limbs continue to develop while the pads, present on the palms and fingertips, recede. Papillary lines do not appear on the surface until week 17. At this time, the relief of the dermis coincides with the grooves of the epidermis. And finally, from week 25, the papillary drawing has its final morphology, which will remain until the skin is destroyed.
The variety of papillary patterns is due to many factors, both genetic (bone morphology, rate of development of the ridges, size and shape of the pads, curvature of the skin, etc.) and environmental (diet and skin movements) pressure difference in amniotic fluid, blood pressure, finger pressure…). This explains why even two identical twins will have similar but not identical papillary designs due to the influence of the environment. This also explains why papillary ridges are unique to each individual. The probability that two people have the same fingerprints is one in 64 billion , hence its use since the 19th century as a means of identifying people.
How can fingerprints be recovered?
When we talk about “recovering” fingerprints, we mean it to refer to forensic science and the way in which fingerprints can be revealed in, for example, a robbery or a crime scene.
In this way, fingerprints can be recovered in a number of ways, such as by using brushes, powders, a magnifying glass, and tape . It is in the crime lab that fingerprints can help identify a criminal or a victim.
Modern forensic scientists now have the power to use a variety of techniques that can help when it comes to improving printed images. Collecting fingerprints is one of the best ways to link an offender to the scene. There are two types of prints. The former are latent prints that require processing to become visible. These prints require the best effort to place in the scene. These prints are the most common type of fingerprint that contains the most amount of evidence. The second is patent prints , which are visible but can be enhanced by post-processing.
Any surface that may contain a footprint can help investigators catch a criminal. Researchers can recover fingerprints from porous surfaces such as unfinished paper, cardboard, and wood that will retain an impression. Non-porous surfaces such as metal, glass, and plastic will not retain an impression; however, the use of powder will help retain the print.