Exam 2 Study Guide

Terminology/concepts

• Friction ridge skin - the skin on your fingers, palms, and soles of your feet that contains raised ridges and recessed furrows

• Ridge detail - the combination of ridge flow, ridge characteristics, and ridge structure of friction ridge skin, as observed and reproduced in an impression

• Types of prints

  • Latent - an impression of the friction ridge skin recorded under accidental or uncontrolled circumstances

  • Patent - friction ridge impression of unknown origin, visible without development (a type of latent print)

  • Plastic - friction ridge impression of unknown origin that is impressed in a soft substrate to create a three-dimensional impression (a type of latent print)

• Negative - no visible/discernible ridge detail

• Insufficient - an impression of the friction ridge skin that does not contain sufficient data to support a reliable conclusion (also referred to as “no value”)

• Substrate - the surface upon which a friction ridge impression is deposited

• Matrix - the substance that is deposited or removed by the friction ridge skin when making an impression

• Quality control - the activities conducted during the course of workflow to ensure that the data and results produced satisfy specified criteria and that equipment or reagents are working as expected (ex: test impressions as positive controls in latents)

• Factors affecting recovery

  • Substrate

    • Clean, smooth surfaces tend to lead to better recovery.

  • Matrix

    • The amount and composition of matrix on the hands or surface at time of deposition can affect recovery (e.g., too much or too little matrix can lead to poor recovery).

  • Environment

    • Friction or wet conditions can adversely affect the preservation of latent prints on certain surfaces.

  • Friction ridge skin

    • Every person’s friction ridge skin is different; some people have poor ridge definition and leave prints that are more difficult to visualize than others.

Physical Development

• Powders

  • Theory

    • The development of fingermarks by powdering occurs by preferential adhesion of powder particles to the ridges, with the background material having less affinity for the particles.

  • Types

    • Granular (black and white)

      • Most are carbon-based

      • Amorphous, elemental carbon with a textured, irregular (but smooth) shape

    • Metal flake

      • Typically aluminum

      • Smooth surfaces and jagged edges

      • Increased surface area

    • Fluorescent

      • Laser dye added in solution to a binder and then mixture is allowed to evaporate

      • Principle of luminescence to provide contrast

    • Magnetic

      • Contains iron particles

      • Applied with a magnetic wand

• Preservation methods

  • Tape lifts

    • Typically transparent tape placed on backing card of contrasting color

    • Tape can be placed on acetate as well.

  • Hinge lifters

    • An adhesive square attached to a backing card by a hinge

  • Gel lifts (opaque)

    • Can be black or white

  • Silicone casting material

    • AccuTrans

      • Pre-made

      • Two components are combined using an application gun

    • Mikrosil

      • Mixed by the analyst before application

  • Photography in situ

Cyanoacrylate Fuming

• Traditional

  • Theory

    • Nucleophile-initiated (typically by water) polymerization of the cyanoacrylate vapors

    • Cyanoacrylate vapors react with the components in fingermark residue (specifically water-soluble amines and carboxylic groups) and then continue to react further with other cyanoacrylate vapors to form a plasticized print.

  • Conditions

    • Humidity 75-90%

    • Heat superglue to about 120 degrees Celsius

  • Enhancement Techniques

    • Powder

      • Black magnetic powder is recommended.

    • Dye stain

      • Rhodamine 6G (excitation 450-550 nm)

      • Ardrox (excitation 250-500 nm)

      • Basic yellow 40 (excitation maximum at 445 nm)

      • MBD

      • RAM (rhodamine 6G, Ardrox, MBD)

      • MRM-10 (rhodamine 6G, Maxilon flavine 10 GFF, MBD)

• Vacuum chamber

  • A vacuum chamber may be used to cause volatilization of cyanoacrylate ester by pressure rather than heat without the addition of humidity.

    • Pressure is reduced to ~200 mtorr using a rotary; evaporation is accelerated and the development time reduced.

    • Prints tend to be translucent and only weakly visible to the naked eye.

  • Some researchers have found that this practice is less effective overall than the use of controlled humidity environments.

Chemical Development

• Reagents to be used with different substrates

  • Porous

    • Indanedione

      • Reacts with amino acids

      • Humidity chamber - 100 degrees, 60% RH

      • Fluorescent

    • Ninhydrin

      • Reacts with amino acids to produce Ruhemann’s purple

      • Humidity chamber - 80 degrees, 65% RH

    • DFO

      • Reacts with amino acids to produce a pale purple color that is lighter than those developed by ninhydrin

      • Product that is colored and fluorescent

      • Requires high heat and low humidity

        • 100 degrees for 40 min

  • Nonporous

    • SG fuming

    • Dye stain

    • Powder

• How each method works

Development Selection & Sequencing

• Factors affecting whether a print can be left on an item

  • Substrate

    • Clean, smooth surfaces tend to lead to better recovery.

  • Matrix

    • The amount and composition of matrix on the hands or surface at time of deposition can affect recovery (e.g., too much or too little matrix can lead to poor recovery).

  • Environment

    • Friction or wet conditions can adversely affect the preservation of latent prints on certain surfaces.

  • Friction ridge skin

    • Every person’s friction ridge skin is different; some people have poor ridge definition and leave prints that are more difficult to visualize than others or don’t leave prints at all.

• Blood reagents

  • Acid yellow 7

    • Acid dye that reacts with proteins and their breakdown components found in blood

    • Prints are colored yellow after treatment and fluoresce under purple/blue light

    • Recommended for nonporous surfaces, although may work on certain porous surfaces

    • Procedure: fixative applied using filter paper for a minimum of 3 minutes; item is submerged in the dye solution for 1-3 minutes then rinsed with rinse solution

  • Amido black

    • Reacts with proteins in blood

    • Safer, permanent procedure that can be used on porous or nonporous surfaces

    • Prevents subsequent serological examination

    • Procedure   

      • Blood proteins are fixed using 5-sulphosalicylic acid

      • Working solution is applied for 30-90 seconds

      • Rinse with first rinse solution followed by second rinse solution and allow to air dry

  • Leucocrystal violet

    • Catalytic test for blood

    • Reduced or colorless form of crystal violet

    • Violet colored dye is formed through a catalyzed oxidation by peroxide when LCV reacts with hemoglobin or its derivatives

    • Porous or nonporous surfaces

  • Ninhydrin

• Amino acid reagents

  • Indanedione

  • Ninhydrin

  • DFO

• Clean technique

  • Use 10% bleach solution to wipe down all surfaces, utensils, and chambers to be used.

  • Always place evidence on clean brown paper.

  • Refrain from marking evidence to reduce the chance of introducing DNA.

  • Work with DNA scientist to determine the best case approach; it may be best for DNA to swab certain areas before LP processing.

• Tape reagents

  • Fluorescent/Gentian violet

    • Used as a stain for epithelial cells and other latent print residues producing an intense purple color.

    • Shown to be effective on adhesive surfaces.

    • Applied by dipping item into solution for approximately 30 seconds; excess solution is removed by carefully rinsing with cold tap water.

  • Wet-Wop

    • Powder suspension

    • Comes in black or white

    • Effective for tape

    • Works by adhering to latent print residues

    • Applied using a camel hair brush; surface must be completely covered for approximately 15-30 seconds; rinse gently with cold tap water and allow to air dry

• Other reagents

  • Sudan black

    • Nonporous surfaces contaminated with greasy or sticky substances

    • Dye which stains the fatty components of sebaceous secretions

    • Can enhance cyanoacrylate ester-developed prints

    • Applied by soaking the item for 2-3 minutes and rinsing the item in cool, running tap water

  • SPR

    • Effective for processing nonporous wet surfaces

    • Suspension of molybdenum disulfide (lipid-sensitive reagent) particles in a surfactant solution

    • Procedure

      • Immerse or spray item for 1 minute, rinse excess reagent in a gentle flow of tap water for approximately 15 seconds, and allow to air dry

Alternate Light Source (ALS)

• Fluorescence

  • After a molecule absorbs light and is raised to a higher energy level, it relaxes back to ground state by giving off energy in the form of light; emission is immediate.

  • Stokes shift: The difference between absorption and emission when materials absorb light and re-emit this light at longer wavelengths

Digital Imaging

• File types

  • RAW: The unprocessed sensor data from a camera

  • JPEG: An image format that reduces the image file size - sacrificing image quality - so that the image does not require as much storage space

  • TIF: A lossless compression format used for storing digital images

• ADAMS

  • Authenticated Digital Asset Management System

  • Calibrate all camera images

  • Automatic authentication

  • Automatic documentation of processing history and chain of custody

  • Open images in Photoshop through ADAMS

BCI Note Taking

• Difference between negative & insufficient/no value

  • “Insufficient” is used for visible ridge detail that does not contain enough quality or quantity of data sufficient for image capture.

  • “Negative” is used for items with no visible ridge detail present.

• Lift/image numbering system

  • Lifts

    • Parent item - Lift # - letter (e.g. 1-1a or 1-1A)

  • Images

    • Parent item - Object # - photo # - letter (1-1-1a or 1-1-1A)

  • A letter is needed of all impressions deemed sufficient and/or borderline