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More On-Scene Considerations

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Presentation on theme: "More On-Scene Considerations"— Presentation transcript:

1 More On-Scene Considerations
Fingerprints III More On-Scene Considerations

2 Forensically Important Surfaces
Nonporous Semi-porous 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 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 Examples Certain plastics Glass Metal surfaces Glazed ceramics Glossy paints NWS=Not Water Soluble WSD=Water Soluble Deposits

3 Print Development Methods

4 Powder Dusting Generally used on nonporous surfaces Lots of Choices

5 Dusting Nonporous Surfaces
Dusting powders used to develop fingerprints since the 19th century 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.

6 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.

7 Print Dusting Powders Choice of Powder Common Powders
Surface characteristics Color of background Detection Method Fluorescent Visual Location Preservation Method Photography Lifting method Tape Gel lifter Liquid gel (Tex Lift) Casting 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

8 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

9 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

10 More Powders Metallic powders Thermoplastic powders Magnetic Fine lead
Metallic flake powders Metal evaporation Gold/silver/aluminum Thermoplastic powders

11 When to Use Specific Powders
Aluminum flake powder should be used where ever possible and applied with a glass fiber brush. Zephyr style squirrel and tapered polyester brushes should be used on surfaces where glass fiber brushes might tangle or clog because of surface contamination – dampness, grease or oil. Dust 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 surfaces. Black or jet-black magnetic powders should be used on u-PVC surfaces. All surfaces may respond better to chemical treatment, and this should be considered before embarking on a fruitless strategy.

12 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

13 Powder Dusting Brushes

14 Zephyr Style Fiber Mounting Artist Style Fiber Mounting
Powder Brushes Feather Duster Zephyr Style Fiber Mounting Tools for powders Brush Types Fiberglass Animal hair Synthetic/natural fiber Feather Magnetic Artist Style Fiber Mounting

15 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

16 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,

17 Magnetic Dustering Brushes
Magnetic Dusting Brush Magnetized Black Powder Black Magnetic Powder

18 Lifting Developed Fingerprints

19 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.

20 Tape lifting was not the correct method. Fingerprint Dusting Powder
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

21 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

22 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.

23 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.

24 Developing Textured Surfaces

25 Powders for Textured & Difficult Surfaces Powder Characteristics
Results of Study – On-scene Application Flake Powders: Metallic flake Aluminum Brass Magenta Flake Metallic flakes lie on surface of ridges - print appear reflective. Ridge detail appears continuous Aluminum: most efficient on glass but works as well as alternatives on other smooth surfaces. Brass (bronze or gold): performs similarly to aluminum but should be used only on smooth silver surfaces where aluminum would have low contrast. Magenta Flake: can be an alternative to black magnetic for dark, textured surfaces. Black Powders: Granular carbon particles with other powders added to change the color. Jet black Gray Other colors Ridge detail can be heavier around sweat pores giving a “granular” appearance. Black granular: To be used on some smooth surfaces only Magnetic Powders: Variations in color based on the addition of other powders Magnetic Powders come in two forms. 1. Single component powder Magnetic particles act as the developing powder. 2. Two component system Magnetic particles acts as a carrier for non-magnetic powder Black magnetic: Most effective on textured and u-PVC surfaces. Other magnetic powders (gray, silver, etc) are not effective and are less sensitive. White magnetic is less sensitive by effective on dark surfaces.

26 Patent Prints in Blood

27 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)

28 Superglue + Black Powder Dusting
Partially bloody fingerprints on Stainless Steel Developed with Ni CTF (right) Compare with superglue + black powder (left) Traditional Superglue + Black Powder Dusting Ni - CTF

29 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.


31 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.


33 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.

34 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.

35 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.

36 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.

37 Generally, Investigators Should Consider the Following.
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.

38 Fingerprint Development Method
Use and Limitations Visualization Examine all items visually because heat & soot affect prints in various ways. Soot may preferentially deposit on oily surfaces. Heat may develop ridge detail on paper. Print residue can bake onto metallic surfaces. Black Powder Suspension (WetWop, etc) Best for non-porous surfaces <200oC Black Magnetic Powder Not useful >200oC Small Particle Reagent (SPR) Less useful than powder suspensions Super glue fuming + Basic Yellow 40 Good up to 500oC on non-porous surfaces Vacuum Metal Deposition Laboratory technique but appropriate up to 900oC. Water or dried water spots can interfere. Porous Surfaces: Protein/amino acid chemicals DFO & Ninhydrin Performs poorly when paper has been wet Physical Developer Develops prints on charred paper in laboratory environment Infra-red imaging Useful for areas where charring & soot deposits: Use view finder of IR Camera. Use lens filter >715nm – RG850 filter. Blood Protein Stains (Acid violet 17, Coomassie blue, Amido black) Good up to 200 oC Blood Presumptive tests: Heme-specific Stains Stops working >150oC

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