Tracing evidence involves carefully locating, collecting, and analyzing microscopic or difficult-to-see materials left at a crime scene or on an object.
One primary method for tracing evidence, especially trace materials like hairs, fibers, glass, soil, and paint, is Hand picking. This technique relies on visual examination and specialized tools to find tiny pieces of evidence.
The Hand Picking Method for Tracing Evidence
Hand picking is a fundamental process used by forensic examiners to search for and collect small, often invisible-to-the-naked-eye evidence. It's a detailed visual inspection of an object or surface.
Key Steps in Hand Picking
The process involves a systematic search for trace materials:
- Visual Examination: The examiner meticulously looks over the object or area of interest.
- Evidence Types: They specifically search for common trace evidence like:
- Hairs
- Fibers
- Glass fragments
- Soil particles
- Paint chips
- Lighting Techniques: To enhance visibility, examiners use various lighting conditions:
- Normal room light
- Oblique lighting (light shone at an angle to cast shadows and highlight surface irregularities)
- Alternate light source (ALS) (using specific wavelengths of light, like UV or blue light, which can cause certain types of evidence to fluoresce or become more visible)
- Magnification: A magnifying glass is often used to aid the examiner's vision, allowing them to spot smaller particles or details that might be missed otherwise.
This methodical approach ensures that potential trace evidence is not overlooked before collection and further analysis.
Tools and Techniques in Hand Picking
| Tool/Technique | Description | Purpose |
|---|---|---|
| Visual Examination | Direct observation of the object/surface. | Initial search for visible evidence. |
| Normal Room Light | Standard ambient lighting. | Basic visibility. |
| Oblique Lighting | Light directed across the surface at a low angle. | Reveals texture and raised/depressed particles. |
| Alternate Light Source | Use of specific wavelengths of light (e.g., UV, blue). | Helps visualize fluorescent materials. |
| Magnifying Glass | Handheld lens providing magnification. | Improves visibility of small details/particles. |
By combining these techniques, examiners can effectively locate tiny pieces of evidence that can be critical in reconstructing events or linking individuals to a scene.
