Lecture: Crime Scene Fingerprint Analysis

Introduction

• Presented by Matt Steiner, Senior Crime Scene Analyst.
• Demonstrated to Louise, Staff Writer at Wired, the process of lifting fingerprints from various surfaces.

Basics of Fingerprint Lifting

Ideal Surfaces

• Smooth and Non-Porous Surfaces: Plexiglas is an ideal surface.
• Use of fingerprint powder (Titanium dioxide with wetting agents for white powder).

Dusting Process

• Coat brush with powder, spin off excess.
• Apply powder slowly using oblique lighting.
• Identify fingerprint pattern (whorl, loop, arch) and follow the ridge detail.

Lifting Fingerprints

• Use fingerprint lifting tape.
• Ensure smooth transfer onto acetate for preservation.

Advanced Fingerprint Lifting

Difficult Surfaces

• Textured or Curved Surfaces: Use Microsil or casting silicone.
• Black powder (carbon agent) for contrast.

Silicone Casting

• Mix Microsil with hardener, spread over fingerprint area.
• Used in cases like tool mark impressions.

Curved and Wet Surfaces

• Fingerprints mainly water; remaining parts are mineral salts, amino acids, lipids.
• Reacting with Lipids: Use solutions like DM disulfide to highlight fats in prints.

Dealing with Complex Situations

Bloody Fingerprints

• Types of impressions: latent, patent, plastic.
• Use leuco crystal violet (with hydrogen peroxide) to develop prints from blood.

Chemical Safety

• Apply chemicals using masks to avoid inhalation.
• Use of filter paper for application.
• Results in a violet color indicating the presence of blood.

Analysis and Further Processing

Photographing and Analysis

• Initial and post-processing photographs of fingerprints.
• Photographic evidence sent to lab for further enhancement.

Database Checking

• Fingerprints analyzed and compared against local, state, and federal databases.

Conclusion

• Comprehensive explanation of fingerprint lifting techniques.
• Emphasis on the importance of careful handling and analysis of evidence in crime scenes.