Forensics Expert Explains How to Lift Fingerprints | WIRED

Summary

In this detailed video, Matt Steiner, a senior crime scene analyst, teaches Louise Matsakis, a staff writer at Wired, how to lift and process fingerprints from various surfaces. The tutorial covers techniques such as using fingerprint powder and tape on smooth surfaces, employing Mikrosil for textured objects, and processing prints on challenging, wet, or bloody surfaces. Matt also discusses the chemicals and tools used for enhancing prints, such as leucocrystal violet for blood. Finally, they explore how recovered fingerprints are analyzed in labs and checked against local, state, and federal databases to identify suspects.

Takeaways

• 😀 Matt Steiner, a senior crime scene analyst, demonstrates fingerprint lifting techniques to Louise Matsakis, a staff writer at Wired.
• 😀 The ideal surface for fingerprint collection is smooth and non-porous, like plexiglass, which is great for lifting fingerprints.
• 😀 Fingerprint powder, made from titanium dioxide, is used with a brush to dust the surface and reveal fingerprints. Oblique lighting helps highlight prints.
• 😀 When dusting a surface, it’s important to apply powder slowly and avoid excess powder, which can obscure the print.
• 😀 Lifting the print is done with special packing tape, which is carefully pressed over the print to lift it without damaging the details.
• 😀 After lifting, the fingerprint is transferred onto an acetate sheet, ensuring it remains clear and free of air bubbles.
• 😀 For difficult surfaces, such as textured or curved objects, Mikrosil (a casting material) is used to recover prints from surfaces like golf balls or vases.
• 😀 On wet surfaces, such as a rain-soaked bottle, the remaining oils in fingerprints can be highlighted using a specialized chemical that reacts with the oils.
• 😀 Bloody fingerprints, or patent prints, can be enhanced using leucocrystal violet, which reacts with the blood’s heme to reveal the print.
• 😀 After recovering fingerprints, they are photographed, documented, and sent to a lab for further analysis, where they may be checked against databases for identification.

Q & A

What is the most ideal surface for lifting fingerprints?

The most ideal surface for fingerprint recovery is something smooth and non-porous, such as plexiglass, which allows for better adhesion of fingerprint powder.

What is fingerprint powder typically made from, and how is it applied?

Fingerprint powder is typically made from titanium dioxide, combined with wetting agents. It is applied by lightly dusting the surface with a brush, ensuring that excess powder is removed by spinning the brush before application.

Why is it important to add powder slowly during fingerprint dusting?

It is important to add powder slowly to avoid applying too much, which could obscure the fingerprint details. The goal is to enhance the ridge patterns without overloading the surface with powder.

What is the purpose of using oblique lighting while dusting for fingerprints?

Oblique lighting helps highlight the fingerprint ridges by casting shadows, making it easier to identify the details of the print on the surface.

What are the steps involved in lifting a fingerprint using tape?

To lift a fingerprint, first apply tape to the surface where the print is located, starting outside the print area. Then, smooth the tape over the print, ensuring there are no air bubbles. Finally, transfer the print to an acetate card, rubbing it to remove any air bubbles.

What is Mikrosil, and when is it used in fingerprint recovery?

Mikrosil is a silicone casting material used for recovering fingerprints or impressions from textured or curved surfaces that are difficult to process using regular powder or tape methods.

How does environmental weather, such as rain, affect fingerprint recovery?

Rain can wash away much of the fingerprint's water-based components, leaving only oils and fatty acids behind. Specialized solutions can react with these oils to enhance the remaining fingerprint details.

What chemical reaction occurs when leucocrystal violet is applied to blood prints?

Leucocrystal violet, when applied to a blood print, reacts with the heme group in blood. This catalytic reaction causes the product to turn purple, helping to enhance the visibility of the fingerprint's ridge details.

What are the three types of fingerprint impressions commonly found at crime scenes?

The three types of fingerprint impressions are latent (invisible prints), patent (prints impressed in a substance like blood or dirt), and plastic (prints left in soft surfaces like clay or putty).

How are recovered fingerprints processed and analyzed after being lifted from a crime scene?

After fingerprints are lifted, they are photographed and sent to a lab for further analysis. The prints are then compared against databases at local, state, or federal levels to identify potential matches.