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Lecture 14: Fingerprints IIB . On-Scene Considerations Continued. 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

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lecture 14 fingerprints iib

Lecture 14:Fingerprints IIB

On-Scene Considerations

Continued

surfaces nonporous
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

SurfacesNonporous

NWS=Not Water Soluble

WSD=Water Soluble Deposits

surfaces 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

Surfaces Semi-porous

WSD = Water sol. Deposits

NWSD = Non water sol. Deposits

slide6

Dusting Nonporous Surfaces

  • Detectives dusting powders to develop fingerprints since the 19th century … trend continues unabated.
    • Study in Great Britain showed that approximately 50% of their on-scene fingerprint identifications came from dusted fingerprints.
  • Powders are the most ubiquitous technique for developing non-porous and selected porous surfaces, and their widespread use should not come as a surprise as the go-to technique of crime scene investigators.
    • IMAGE: Black powder laden brush … swishing back and forth … bespectacled eyes leaning through a suspended black dust cloud … ridge detail slowly emerges through the haze.
      • Image is false, of course, but experience shows that the aftermath of processed crime scenes sometimes appear as though a black tornado had swept though the scene
  • Since the early days of black-only powder, a growing list of dusting powders is available from commercial suppliers complicating the selection process.
slide7

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.
    • Each category has specific formulation and characteristics that affect its interaction with fingerprint residue, the surface and its ultimate visibility.
    • Limited, in-depth guidance concerning which powder to use in a specific circumstance.
  • Factors influence the success of powder dusting, some of which are not under the control of the scene scientist/investigator … affect how well a particular powder adheres to the print emulsion.
    • Nature and condition of the surface,
    • Clarity of the ridge detail
    • Age.
    • Equipment. … plethora of powders and powder brushes from which to choose, and the reason why an examiner chooses … choice usually based on experience with a particular product, the nature of the surface, word of mouth and preferences of a the crime scene unit.
  • Often not based on a rigorous evaluation of specific powder/brush combinations used for a specific application.
physical methods dusting with powders
Physical Methods Dusting with 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
powder types
Powder Types
  • 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
powder types1
Powder Types
  • Metallic powders
    • Magnetic
    • Fine lead
    • Metallic flake powders
    • Metal evaporation
    • Gold/silver/aluminum
  • Thermoplastic powders
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
    • Iron grit mixed with either Al or Cu flake powder
    • Iron grit milled to 10-25un + stearic acid (3-5% w/v)
      • Use rare-earth magnetic rod
    • Can have fluorescent additives
    • Magnetic applicators
      • Powerful rare-earth magnets
      • Permanently magnetized steel rods
    • Textured surfaces – not vertical
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
physical methods powders
Physical MethodsPowders
  • Tools for powders
    • Brush Types
      • Fiberglass
      • Animal hair
      • Synthetic/natural fiber
      • Feather
      • Magnetic

Feather Duster

Zephyr Style Fiber Mounting

Artist Style Fiber Mounting

  • glass, u-PVC, gloss painted wood (un-cleaned),
  • gloss painted wood (cleaned) and painted automotive metal.
slide15

Fingerprint Brushes & Smooth Surfaces

  • Research: the HOSDB evaluated brushes used with aluminum powders on smooth surfaces … Large number of brushes are available, they fall generally into two major classes ‘zephyr’ and ‘artist’ style fiber mountings.
  • Zephyr style mountings : … made from synthetic fibers where the fibers are straight-cut, long and attached to a handle.
  • Mop or Artist Style: … Fiber bundle are rounded.
  • 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 .
  • 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.
  • Results:Un-starched glass fiber brushes were superior to squirrel, polyester, nylon feather brushes, whether the brush was had zephyr or artist mount.
  • Slightly damp, greasy or sticky surfaces had problems. … brush was used too vigorously because of the tendency of brush fibers to tangle.
  • Squirrel zephyr type and the tapered polyester (Tetra washable) are 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, which is undesirable.
slide16

Textured Surfaces

  • Textured surfaces are also commonly encountered at scenes and they present a different challenge than smooth surfaces 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.
    • Zephyr style squirrel and tapered polyester brushes used on surfaces where glass fiber brushes might tangle or clog because of surface contamination – dampness, grease or oil.
  • Glass evidence with aluminum powder unless there is the possibility of contamination and tangling of the glass fiber brush.
  • Black or jet-black magnetic powders should be used on textured & u-PVC surfaces.
  • Some surfaces respond better to chemical treatment,
    • Considered before blindly dusing.
magnetic dusters
Magnetic Dusters

Magnet

Magnetic Dusting Brush

Magnetized

Black Powder

Black Magnetic Powder

slide19

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 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.

slide20

Tape lifting

  • On perfectly flat, smooth surfaces, tape lifting is the fastest and easiest method for lifting dusted prints. Interestingly, the tape lifting process does not always 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

slide21

Silicone (MikrosilTM ) Casting

  • Mikrosiland other brands of silicone casting materials work well with dusted prints on textured surfaces.
  • 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

slide22

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, so if the choice is to use a gellifter, the one to use is determined by the color of the dusting powder, which should contrast well with the color of the gellifter surface. The color can follow the same sequence as the color of the fingerprint lift card in the section on dusting above.
slide23

Tex-lifts

  • Tex-lifts are liquid glues that painted over the developed print. As a liquid, can capture ridge detail on slightly textured surfaces.
  • The Tex-lift liquid is a light blue color that dries clear, so the color of the powder is unimportant, as long as it contrasts with the surface.
  • After the Tex-lift dries, the captured print is lifted with lifting tape (or gellifter) and placed onto a fingerprint lift card of an appropriate color.
powders for textured and difficult surfaces

Dusting Textured Surfaces

Powders for Textured and Difficult Surfaces
  • Textured surfaces commonly encountered at scenes.
  • Pose a different challenge than smooth surfaces because powder particles can become trapped in the surface crevices.
slide27

Fingerprints and DNA

  • British studied powder dusting on ability to obtain usable DNA profiles.
  • Lifting fingerprints using traditional lifting methods – tape and gels - does not quantitatively capture the DNA.
  • After lifting, the area should be swabbed to collect the remaining cellular material present.
  • Study reported obtaining partial DNA profiles using sensitive DNA analysis techniques from lift and swabs taken from the lifted area.
  • Magnetic powder dusting reduces the chance of contaminating a fingerprint’s DNA with that of another.

Create Secondary Powder Source by removing

Powder from original container to secondary container

Take Powder from

Secondary Source

Original Powder Source

Secondary Powder Source

  • Slim possibility of contaminating a fingerprint’s DNA with another after using the same brush and powder …
  • Use clean brushes and fresh powder between dusting.
  • Do not mix used and fresh dusting powder by releasing the used powder into the original reservoir.
slide29

Developing Patent Prints

  • 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
  • Assignment
  • Devise strategy for developing and archiving the entire print.
  • Consider whether latent part of the print might also be in blood visibly below the detection limits of the human eye;
  • Well known that the human eye does not easily perceive low concentrations of blood … not unusual for investigator to “miss” low blood detail.
  • The students’ opinions were split into two strategies.

Partial Bloody Fingerprint

Stained with Coomassie Blue

slide30

Partially bloody fingerprints on Stainless Steel developed with Ni CTF (right)

compared to superglue + black powder

(left)

Traditional

CTF

slide31

Strategy One

  • Dust the sebaceous secretions to develop the latent part of the print,
  • Photograph the dusted print,
  • Lift the dusted print using either tape or a gel lifter
  • Stain the patent part of the print using Acid Violet 17 or Acid Black 1 (Amido Black) for blood proteins.
slide33

Strategy Two

  • Fix the proteins in the patent part of the print using sulfosalicylic.
  • Stain the blood proteins using Acid Violet 17 or aqueous-based Acid Black 1. Note: Using aqueous-based staining solutions run the risk of washing away DNA present. Using organic-based staining solutions run the risk of dissolving fingerprint emulsion that would preclude subsequent dusting.
  • Photograph the developed patent print,
  • Dust the print to visualize the oils in the latent part of the print
  • Lift using tape or gel lifter.
slide35

Fingerprints and Heat: Fire Scenes

  • Arsonists and terrorists handle accelerants, explosives and incendiary devices … these are considered fire and explosion debris. Incendiary devices … Molotov Cocktails … can have prints.
  • A misperception is that the fire and/or explosive environment destroys fingerprints. NOT TRUE … literature on the persistence of fingerprints at arson scenes and on incendiary devices is scanty and often anecdotal.
  • 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.
  • Rooms adjacent to the point of origin which received extensive heat and smoke gave identifiable prints. Non-porous objects in or close to the point of origin rarely gave identifiable prints.
  • Just as it is likely that useable fingerprints can be found at arson scenes, the same is true for incendiary devices, although the body of literature is even scantier.
  • It is possible to uncover prints at arson scenes, the question is how much heat can this fragile evidence withstand. Some studies have been designed to address this topic.
slide36

Fingerprints and Heat

  • Fingerprints can withstand the temperatures measured at arson scenes.
  • 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 to this much heat is a problem because none of the standard protein staining methods or presumptive blood tests work; catalytic tests, fail at temperature below 150oC.
    • 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.
slide37

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.
slide38

On-scene Activity

  • Knowledge of the literature, where investigators reported success,
  • Knowledge of research results … 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.