LATENT FINGER PRINT 5marks shorts notes
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latent fingerprint forensic science short notes
Latent Fingerprints - Short Notes (5 Marks)
Definition
A latent fingerprint is an invisible or barely visible impression of the friction ridge skin (papillary ridges) left on a surface when a finger touches it. The word "latent" comes from the Latin latens, meaning "hidden." These prints are deposited by the natural secretions of sweat glands and sebaceous (oil) glands present on the ridges of the fingertips.
Types of Fingerprints (Classification by Visibility)
Fingerprints at crime scenes are categorized into three types:
| Type | Description |
|---|---|
| Latent | Invisible to the naked eye; require development techniques |
| Patent | Visible without enhancement (e.g., prints in blood, grease, paint) |
| Plastic | Three-dimensional impressions in soft materials (wax, putty, clay) |
Composition of Latent Prints
Latent prints consist of:
- Eccrine sweat (from sweat glands) - water, amino acids, salts, urea
- Sebum (oily secretions from skin/hair) - fatty acids, lipids
- Contaminants - cosmetics, food, chemicals inadvertently picked up by the fingertip
Development / Visualization Techniques
Since latent prints are invisible, they must be "developed" using physical or chemical methods:
1. Physical Methods
- Fingerprint Powder (Dusting) - Most common technique; aluminum powder (for dark surfaces), carbon/graphite powder (for light surfaces), or fluorescent powders are brushed onto the surface; the powder adheres to the oily/sweat residue
- Vacuum Metal Deposition (VMD) - Gold and zinc are vaporized in a vacuum chamber; useful on plastic surfaces and fabrics
- Small Particle Reagent (SPR) - Used on wet surfaces; molybdenum disulfide particles adhere to lipid components
2. Chemical Methods
- Ninhydrin - Reacts with amino acids in sweat; produces a purple color (Ruhemann's purple); used on porous surfaces (paper, cardboard)
- DFO (1,8-Diazafluoren-9-one) - Fluorescent reagent; reacts with amino acids; used before ninhydrin; enhances older prints
- Cyanoacrylate Fuming (Superglue) - Cyanoacrylate vapor polymerizes on the moisture of sweat residue, forming a white deposit; excellent for non-porous surfaces (glass, plastic, metal)
- Luminescent techniques - Silver nitrate reacts with chlorides in sweat; turns brown on exposure to UV light
3. Alternate Light Source (ALS)
- Laser or high-intensity light at specific wavelengths causes print residue (or fluorescent developers) to fluoresce; used with barrier filters
Surfaces and their Suitability
- Porous surfaces (paper, wood, cardboard) - Chemical methods preferred (ninhydrin, DFO)
- Non-porous smooth surfaces (glass, metal, plastic) - Powdering, cyanoacrylate fuming
- Wet surfaces - SPR or gentian violet
- Curved/complex surfaces - Vacuum metal deposition or gelatine lifters
Significance in Forensic Science
- Personal Identification - Fingerprints are unique to every individual; even identical twins have different ridge patterns. They remain unchanged from birth to death.
- Criminal Investigation - Latent prints link a suspect to a crime scene.
- AFIS (Automated Fingerprint Identification System) - Developed prints are scanned and matched against criminal databases.
- Evidence value - Latent prints are admissible in court and have been used as evidence for over 100 years.
Key Points to Remember
- Latent prints are not visible to the naked eye - they need development
- Deposited by eccrine sweat + sebum from friction ridges
- Development method depends on the type of surface (porous vs. non-porous) and environmental conditions
- Cyanoacrylate fuming is widely used for non-porous surfaces; ninhydrin for porous surfaces
- Ridge details used for comparison: minutiae (ridge endings, bifurcations, dots, short ridges)
- Uniqueness of fingerprints is the foundation of their forensic value
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