searching for, enhancing and reocvering fingerprints from crime scenes

what are fingerprints?

• Ridges on tips of fingers

• Folds in outer layer of skin, the epidermis

how do fingerprints adhere to surfaces?

• Along tops of ridges are minute pores from which sweat is exuded

• Transfers/adheres to surface touched

why do we have fingerprints?

• Friction helps grip objects and sense of touch, help protect from injury

at crime scene

• Plastic-impressed marks

• Patent - visible contaminant/residue, contrast against background

• Latent - require enhancement, not readily visible

Sequential scene examination- always done at end as powder is contaminant

• Visual examination

• Use of oblique lighting

• Photography-non-destructive

• Recovery of any forensic material - trace, DNA and other forensic evidence

• Enhancement

• Recovery

• Clean down

 

visible (patent) fingerprints

See with naked eye

Transparent material e.g. oil grease

Contaminated impressions

Impressions in dust

Impressions in soft material / putty /easter egg

Impressions caused by reaction between surface and fingerprint e.g. on silverware

fingerprints left:

Fingerprints in blood-patent can find latent aswell

Fingerprints left on surfaces

Fingerprint in soft material e.g. putty, blue tack, putty

latent fingerprints

Must be enhanced

Where found?

Where has offender touched? e.g. point of entry

How do we locate them? - put ourselves in offenders shoes

enhancement types of powder

Flake - thin layers

Granular - tiny circular beads

Fluorescent - granular

Magnetic (flake and granular)

flake powders

• Metallic flake introduced in 1970

• Best for smooth, clean, dry surfaces

• Aluminium or magenta

• Bronze/gold

• Can be lifted due to nature of flat surface

• Applied with carbon fibre - zephyr brush

granular powders

• Available in black and white

• Resemble ball bearing coated in carbon

• Practice varies on lifting or not lifting and photography

• Should be use on flaky paint and textured surfaces

• Applied with an animal-hair or synthetic brush

• Some don’t lift because it can squash the 'balls' and only photograph

magnetic powders

• Granular or flake

• Applied using magnetic wand

• Instant results on paper, but less sensitive than chemicals

• Photographed or lifted - flake or granular

fluorescent powders

• Granular

• Applied with animal-hair or synthetic brush

• Magnetic fluorescent powders available

• Fluoresce using UV light source

• Useful when surface is contaminated or is multi-coloured

application of magnetic powder

• Load magnetic wand with powder

• Cascade powder over area- use powder as brush

• Do not let wand touch area

• Use clean brush to lightly 'clean out' mark

• Photograph and/or lift using fingerprint tape/gel and secure to an acetate sheet

fingerprint brushes

how do we recover and what?

Photography

Use a gel lifter or J-Lar lifting tape

3D marks can be cast (Provil)

Blurred or partial marks should be lifted

Several fingerprints from same hand can be lifted together

Articles baring forensic evidence should have this evidence recovered before fingerprinting

lifting fingerprints/friction ridge detail

information required on lift

fingerprint lift

documented recovered marks

• Make accurate record of where prints were found

• Gravity marks or directional arrows should be included to indicate orientation of lift

• Gravity arrows on portable items should point to bottom of item

• Diagrams with measurements to fixed points

• 'score' edges of tape on acetate and sign

items recovered for chemical treatment

Porous surfaces(absorbent materials)

• Paper: documents, letters, books, envelopes

• Cardboard: boxes, packaging

• Wood (unfinished): furniture, crates

Semi-porous surfaces (treated/finished surfaces)

• Painted wood: doors, furniture

• Flossy magazines or photos

• Plastic- coated paper

Miscellaneous items

• Weapons and tools: knives, guns, screwdrives

• Money and coins: paper bills, coins (metal)

• Electronic devices: phones, tablets, remote controls

• Containers: jars, bottles, cans

 

chemical treatment

• Amido black

Proteins in blood and body fluids

Porous and non-porous (high colour on some porous backgrounds)

• Ninhydrin and DFO

Amino acids

Paper and porous surfaces

• Small particle reagent (SPR)

Fatty constituents of fingerprint

Non-porous surfaces

• Superglue (cyanoacrylate vapour)

Water and possibly other constituents of fingerprint

Non-porous surfaces (rough surfaces, vinyl + rubbers)

IF CHOOSE NOT TO LIFT OR DEVIATE FROM SOP THEN DOCUMENT IN MO SECTION and note reason