Lecture 14 fingerprints iib
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Lecture 14: Fingerprints IIB . More On-Scene Considerations . Characteristics Do not absorb at all Emulsion deposit remains Until removed Degraded via environmental effects Fragile NWS Readily removed by organic solvents WSD readily removed by water. Examples Certain plastics Glass

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Lecture 14: Fingerprints IIB

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Lecture 14 fingerprints iib

Lecture 14:Fingerprints IIB

More On-Scene Considerations


Forensically important surfaces

Characteristics

Do not absorb at all

Emulsion deposit remains

Until removed

Degraded via environmental effects

Fragile

NWS Readily removed by organic solvents

WSD readily removed by water

Examples

Certain plastics

Glass

Metal surfaces

Glazed ceramics

Glossy paints

Forensically Important Surfaces

Nonporous

Semi-porous

  • Intermediate characteristics

    • Absorbs WSD slowly

      • Minutes to hours

    • NWSD remains on surface

      • 1 day to several days

      • Some NWS remains longer

  • Examples

    • Certain plastics

    • Waxed surfaces

    • Varnished wood

    • & Some

      • Wall paints

      • Wall papers

NWS=Not Water Soluble

WSD=Water Soluble Deposits


Print development methods

Print Development Methods


Powder dusting

Powder Dusting

Generally used on nonporous surfaces

Lots of Choices


Lecture 14 fingerprints iib

Dusting Nonporous Surfaces

  • Dusting powders used to develop fingerprints since the 19thcentury

    • Study in Great Britain showed that approximately 50% of their on-scene fingerprint identifications came from dusted fingerprints.

    • Most ubiquitous technique for developing non-porous and selected porous surfaces,

      • Experience : Black powder laden brush … swishing back and forth … bespectacled eyes leaning through a suspended black dust cloud … ridge detail slowly emerges through the haze.

  • Growing list of dusting powders available from commercial suppliers

    • Complicate the selection process.


Lecture 14 fingerprints iib

Dusting Nonporous Surfaces

  • Powders are designed to solve surface-related problems … texture, porosity, color, cleanliness and etc.

    • Most grouped into a relatively small number or categories depending on their chemical composition and particle size or shape.

      • Specific formulation and characteristics that affect interaction with fingerprint residue, the surface, and its ultimate visibility.

  • Limited, in-depth guidance concerning which powder to use in a specific circumstance.

  • Many factors influence the success of powder dusting,

    • Some not under the control of the scene scientist/investigator

    • Nature and condition of the surface,

    • Clarity of the ridge detail

    • Age of the print

    • Equipment. …

      • Plethora of powders and powder brushes from which to choose,

        • Examiner typically chooses one based on

          • Experience with a particular product,

          • Nature of the surface

          • Word of mouth

          • Preferences of a the crime scene unit.


Print dusting powders

Print Dusting Powders

  • Common Powders

    • Black powders

      • Ferric oxide

      • Manganese dioxide

      • Lampblack powder

    • White powders

      • Titanium oxide

      • Chalk-titanium oxide

    • Gray powders

      • Chemist gray powder

      • Lead carbonate powder

      • Aluminum flake

  • Choice of Powder

    • Surface characteristics

    • Color of background

    • Detection Method

      • Fluorescent

      • Visual

    • Location

  • Preservation Method

    • Photography

    • Lifting method

      • Tape

      • Gel lifter

      • Liquid gel (Tex Lift)

      • Casting


More powders

More Powders

  • Organic powders

    • KI/cornstarch

    • Calcium sulfate/dihydrate cornstarch

  • Luminescent (fluorescent & phosphorescent powders

    • Acridine orange & yellow

    • Coumarin 6

    • Crystal violet

    • Nile blue

    • Rhodamine B & 6G

    • Phenothiazine

      • Largely dependent on background colors & luminescent properties

    • Other commercial preparations

Prints Developed with Fluorescent Powder


Powder characteristics

Powder Characteristics

  • Fluorescent – used commonly for currency/documents

    • Sprayed in areas where thefts commonly take place

    • Good for multicolored papers

  • Magnetic – Different formulations

    • Two different preparations

    • Can have fluorescent additives

    • Magnetic applicators

      • Powerful rare-earth magnets

      • Permanently magnetized steel rods

    • Textured surfaces – not vertical


More powders1

More Powders

  • Metallic powders

    • Magnetic

    • Fine lead

    • Metallic flake powders

    • Metal evaporation

    • Gold/silver/aluminum

  • Thermoplastic powders


Powder dusting precautions

Powder Dusting Precautions

  • Over dusting

    • “Wash” by pressing lifter against print gently

    • Lifter removes excess powder

  • Too much brushing smears ridges

  • Sweaty or dirty fingers or made from someone with “firm” grip

    • Friction ridges may spread out

    • Too much sweat leaves a smudge

  • Perspiration & grease on FP’s absorb into porous surfaces (paper/cardboard)

    • Powders may not be successful

    • Magnetic brushes don’t leave excess powder


Powder dusting brushes

Powder Dusting Brushes


Powder brushes

Powder Brushes

  • Tools for powders

    • Brush Types

      • Fiberglass

      • Animal hair

      • Synthetic/natural fiber

      • Feather

      • Magnetic

Feather Duster

Zephyr Style Fiber Mounting

Artist Style Fiber Mounting


Lecture 14 fingerprints iib

Fingerprint Brushes & Smooth Surfaces

  • Research: the HOSDB evaluated brushes used with aluminum powders on smooth surfaces.

    • The study used aluminum flake powder for prints aged 24 hours to 7 days

      • glass, u-PVC, gloss painted wood (un-cleaned), gloss painted wood (cleaned) and painted automotive metal.

  • Selecting the correct brush is important because if dusting is done incorrectly or with a heavy hand, the ridge detail can be obscured or destroyed .

    • Un-starched glass fiber brushes superior to squirrel, polyester, nylon feather brushes, whether zephyr or artist mount.

  • Precautions

  • Slightly damp, greasy or sticky surfaces had problems. …

    • Tendency of brush fibers to tangle.

      • Squirrel zephyr type and & tapered polyester good alternatives because they are less prone to tangling.

      • Brushing technique and found that spinning the brush caused glass fiber brushes to tangle more easily


Lecture 14 fingerprints iib

Textured Surfaces

  • Textured surfaces present a challenge because powder particles can be trapped in the surface crevices.

  • Generally two powders reflect the choice of most scene investigators:

    • Aluminum flake and - British

    • Black granular powder - American investigators.

    • Other choices available from commercial forensic supply sources,

      • metallic powders, black, gray (dual), fluorescent, magnetic, bichromatic, powder formulation.

  • Aluminum flake powder:

    • Used where possible & applied with a glass fiber brush.

      • Dust glass evidence with aluminum powder unless possibility of contamination and tangling of glass fiber brush.

  • Black or jet-black magnetic powders should be used on textured & PVC plastic surfaces.

  • Some surfaces respond better to chemical treatment,


Magnetic dustering brushes

Magnetic Dustering Brushes

Magnet

Magnetic Dusting Brush

Magnetized

Black Powder

Black Magnetic Powder


Lifting developed fingerprints

Lifting Developed Fingerprints


Lecture 14 fingerprints iib

Lifting Developed Prints

  • Powder lifts

    • After developing and photographing, lifting is next step. The process, like many on-scene manipulations, is deceptively easy, but skill is involved.

    • The skill is intellectual: Thinking through the Situation

    • First consideration is surface.

  • Surface Texture

  • Prints on all surface types, and once developed, remain on that surface. One is the surface texture. The photographs illustrate the point.

a

b

‘a’ Shows what appears to be a smooth wall in a home where fingerprints are suspected.

‘b’ Shows the actual texture of the wall.


Lecture 14 fingerprints iib

Tape lifting

  • On perfectly flat, smooth surfaces, tape lifting is the fastest and easiest for lifting dusted prints.

    • Tape lifting does not usually lift the entire dusted print

    • Some print detail stays behind, including some of the DNA.

  • Problems with surface texture. Suppose tape was used to lift prints. When the lifted is transferred print to a fingerprint card and examined, you will see gaps in the friction ridge detail.

  • Tape lifting was not the correct method.

  • The result could be inability of latent print examiner to adequately compare the print.

  • The undulating line (green) represents the wall, the black dots are the black powder dusted print ridges and the blue line is the lifting tape.

  • The assumption is that the print penetrates part way into the depth (depending on pressure applied) of the textured surface. The dusted ridges also extend partway into the recesses of the texture.

  • When lifting, the tape does not extend into the texture because it is fairly rigid and not easily moldable to textured surfaces. The result is a partially lifted print, where the only dust (print) that was lifted was where the tape came into contact with the powder on the higher surfaces.

Fingerprint Dusting Powder

Fingerprint Lifting Tape


Lecture 14 fingerprints iib

Silicone (MikrosilTM ) Casting

  • Mikrosil (silicone casting materials)works well on textured surfaces.

  • Diagram below:

    • The pliable silicone, (purple) conforms to the texture of the surface and engulfs the dust-developed print.

    • When the silicone hardens and is removed, its adhesive forces (stickiness) entrap the dust on the print ridges and lift it intact.

    • The lifted mold can be fixed to a fingerprint card to preserve it. Preparing the silicone casting material simply a simple matter of following the directions from the manufacturer.

Mikrosil Covering Surface Texture

Fingerprint Dusting Powder


Lecture 14 fingerprints iib

Gellifters

  • Gel lifters (gellifters)

    • Commercially available in the form of rubber or acetate backed flexible gelatin.

  • Malleability

    • Between tape and silicone

    • Sufficient “give” and stickiness to capture ridge detail in the examples shown above but not if the texture runs too deep.

  • Gellifters are black, white and clear,

    • Choose gellifter by the color of the dusting powder,

      • Should contrast well with the color of the gellifter surface.


Lecture 14 fingerprints iib

Tex-lifts

  • Tex-lifts are liquid glues that painted over the developed print.

    • Liquid that captures ridge detail on slightly textured surfaces

  • The Tex-lift liquid is a light blue color that dries clear,

    • Color of the powder is unimportant, as long as it contrasts with the surface.

  • After the Tex-lift dries, capture print by lifting with lifting tape (or gellifter) and

    • Place onto a fingerprint lift card of an appropriate color.


Developing textured surfaces

Developing Textured Surfaces


Patent prints in blood

Patent Prints in Blood


Lecture 14 fingerprints iib

Developing Patent Prints in Blood

  • Problem:

  • Developing partial bloody fingerprint on concrete block painted white, glossy paint.

  • Only the middle part of the print, approximately 1/3 of the ridge detail was visible, and it was in blood.

  • Assume visible ridges in blood

Partial Bloody Fingerprint

Stained with Coomassie Blue (Protein Stain)


Lecture 14 fingerprints iib

Partially bloody fingerprints on Stainless Steel

Developed with Ni CTF (right)

Compare with superglue + black powder

(left)

Traditional

Superglue + Black Powder Dusting

Ni - CTF


Lecture 14 fingerprints iib

Fingerprints and Heat: Fire Scenes

  • Assume:

    • Arsonists and terrorists handle accelerants, explosives and incendiary devices … these are considered fire and explosion debris. Incendiary devices … Molotov Cocktails … can have prints.

  • Misperception:

    • Fire and/or explosive environment destroys fingerprints.

    • Research shows that fingerprints can persist at high temperatures, especially if carbon (soot) covers them.

      • In experiments, fires purposely set with containers of a kerosene/gasoline mixture used to start the fire and then left inside the burning building.

      • After extinguishing the fire using ordinary efforts, containers were recovered.

      • Attempts to locate fingerprints on those items a few feet from the point of origin were unsuccessful.


Lecture 14 fingerprints iib

Fingerprints and Heat: Fire Scenes

  • Rooms adjacent to the point of origin gave identifiable prints.

    • Non-porous objects in or close to the point of origin rarely gave identifiable prints.

  • Prints also can be found on incendiary devices,

    • Body of literature is even scantier.

  • How much heat can such fragile evidence withstand.

    • Some studies have been designed to address this topic.


Lecture 14 fingerprints iib

Fingerprints and Heat

  • Fingerprints can withstand temperatures of at least 300o C.

    • The recovery of useful marks coved by heavy soot deposits might withstand temperatures up to 700o C or more.

  • Fingerprints in blood and the problem of how much heat they can withstand. Experiments suggest that blood prints survive heat up to approximately 200oC.

    • Developing blood prints exposed 200 is a problem because none of the standard protein staining methods or presumptive blood tests work

      • Catalytic tests fail at temperature below 150oC.

      • Protein staining reagents might be successful at 200 C

    • Blood forms a protective layer on the surface before flaking off which means that the surface oxidation between the ridge detail (blood covered ridges) and those non-protected areas (the grooves) is different.

  • Processes sensitive to the surface conditions, e.g., Vacuum Metal Deposition, can develop prints where blood prints have been exposed to temperatures as high as 900oC.


Lecture 14 fingerprints iib

Locating Fingerprints at Arson Scenes

  • Finding them should be a priority. Knowing where to look is the problem because items of potential evidence at arson scenes may be soot covered. One consideration is temperature.

  • Gauge the hottest points at the scene and then confine collecting evidence in areas where temperatures did not rise above 300oC.

    • Temperatures above 200o C destroy the organic components of the fingerprint residue, leaving inorganic salts, unless protected.

  • Fire suppression.

    • Water not usually detrimental to the oils in fingerprint residue because they are insoluble.

    • If fire hot enough to destroy the organic components of exposed residue (>200o C), only inorganic salts will be left, which are soluble in water.

    • Fire suppression efforts may dissolve these salts and efforts to develop prints will be futile.

  • Metallic surfaces.

    • There is the possibility that the print residue may act as resist against oxidation such that the unprotected metal might etch.

    • Additionally, soot can protect fingerprints, which means that soot covered, potentially probative evidence should always be considered as potential sources of retrievable evidence.

      • Soot causes problems in the laboratory because scientists must remove the soot without destroying the prints.


Lecture 14 fingerprints iib

On-scene Activity

  • Knowledge

    • Know the literature – Know where investigators reported success,

    • Know the research … answered questions concerning the effects of temperature, accelerant, etc.

  • Generally, Investigators Should Consider the Following.

  • Less than 300o C … retrievable

  • Evidence protected from direct exposure to heat and smoke may give retrievable fingerprints.

  • Less soot covering fingerprints is better because the soot cover must be removed in the laboratory. Heavy soot deposits, however, does not mean removal techniques will not be successful.

  • Dry evidence has a better chance of providing probative fingerprint detail than wet.

  • Dried fingerprint residue … re-humidification may be successful, but the possibility of destroying the ridge detail is a concern.


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