Latent fingerprints, invisible to the naked eye, are transferred when the natural oils and sweat on a person's skin are deposited onto a surface. This process occurs through direct contact.
The Mechanism of Transfer
The transfer of a latent print involves the following steps:
- Deposition: The body's natural secretions (oils and sweat) present on the ridges of fingertips come into contact with a surface.
- Adhesion: These secretions adhere to the surface, leaving behind a thin, invisible impression of the friction ridge skin pattern.
- Secondary Transfer: In some cases, a latent print can be transferred indirectly. This occurs when a print already deposited on one surface is then transferred to another surface. For example, a print on a plastic bag might be transferred to a different object it touches. This is referred to as secondary or tertiary transfer and can happen when a printed surface comes into contact with a sticky or adhesive surface. (e.g., Secondary and tertiary transfer of latent fingermarks using a sticky ...)
Types of Surfaces and Transfer
Latent prints can be found on a variety of surfaces, both porous (like paper) and non-porous (like glass). However, the success of transfer and the clarity of the resulting print are affected by several factors, including the surface's texture and the environmental conditions. (e.g., Latent Print Development, Post-transfer conditions... affect the quality of latent prints after deposition)
- Examples of successful transfer: Smooth surfaces, like glass or metal, often yield clearer prints than rough, porous surfaces.
- Examples of challenges: Porous surfaces can absorb the oils and sweat, making the print more difficult to develop.
Detection Methods
Because latent prints are invisible, specialized techniques are used to visualize them for analysis. These include:
- Fingerprint powders
- Chemical reagents
- Alternate light sources
(e.g., Fingerprint Analysis: How It's Done, What Police Officers Need to Know About Latent Prints | FAQs*)
