Transcript Black powders

Fingerprints III
More On-Scene Considerations
Forensically Important 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
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Certain plastics
Glass
Metal surfaces
Glazed ceramics
Glossy paints
Semi-porous
 Intermediate characteristics
 Absorbs WSD slowly
 Minutes to hours
 NWSD remains on surface
 1 day to several days
 Some NWS remains longer
 Examples
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Certain plastics
Waxed surfaces
Varnished wood
& Some
 Wall paints
 Wall papers
NWS=Not Water Soluble
WSD=Water Soluble Deposits
Print
Development Methods
Powder Dusting
Generally used on nonporous surfaces
Lots of Choices
Dusting Nonporous Surfaces
 Dusting powders used to develop fingerprints since the 19th
century
 Study in Great Britain showed that approximately 50% of their onscene 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.
Dusting Nonporous Surfaces
 Powders are designed to solve surface-related problems … texture, porosity,
color, cleanliness and etc.
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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,
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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
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Equipment. …
 Plethora of powders and powder brushes from which to choose,
o
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
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
 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
More Powders
 Organic powders
 KI/cornstarch
 Calcium sulfate/dihydrate cornstarch
 Luminescent (fluorescent &
phosphorescent powders
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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
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 Powders
Metallic powders
 Magnetic
 Fine lead
 Metallic flake
powders
 Metal
evaporation
 Gold/silver/alumi
num
Thermoplastic
powders
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 Brushes
Feather Duster
Zephyr Style Fiber
Mounting
 Tools for powders
 Brush Types
 Fiberglass
 Animal hair
 Synthetic/natural fiber
 Feather
 Magnetic
Artist Style Fiber
Mounting
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
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:
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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
Magnet
Magnetic Dusting Brush
Magnetized
Black Powder
Black Magnetic Powder
Lifting Developed Fingerprints
Lifting Developed Prints
 Powder lifts
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After developing and photographing, lifting is next step. The process, like many
on-scene manipulations, is deceptively easy, but skill is involved.
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The skill is intellectual: Thinking through the Situation
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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.
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.
Fingerprint Dusting Powder
Fingerprint Lifting Tape
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.
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
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.
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.
Tex-lifts
Developing
Textured Surfaces
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 Aluminum: most efficient on glass but works as well as alternatives on
- print appear reflective.
other smooth surfaces.
Ridge detail appears continuous
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.
Ridge detail can be heavier around
sweat pores giving a “granular”
appearance.
Black granular: To be used on some smooth surfaces only
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 nonmagnetic 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.
Jet black
Gray
Other colors
Magnetic Powders:
Variations in color based on the
addition of other powders
Patent Prints in Blood
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)
Partially bloody
fingerprints on
Stainless Steel
Developed with Ni
CTF (right)
Compare with
superglue + black
powder
(left)
Traditional
Superglue + Black Powder Dusting
Ni - CTF
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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.
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.
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.
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.
Fingerprint Development Method
Visualization
Use and Limitations
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)
Black Magnetic Powder
Small Particle Reagent (SPR)
Super glue fuming + Basic Yellow 40
Vacuum Metal Deposition
Porous Surfaces: Protein/amino acid chemicals
DFO & Ninhydrin
Physical Developer
Infra-red imaging
Blood Protein Stains (Acid violet 17, Coomassie
blue, Amido black)
Blood Presumptive tests: Heme-specific Stains
Best for non-porous surfaces <200oC
Not useful >200oC
Less useful than powder suspensions
Good up to 500oC on non-porous surfaces
Laboratory technique but appropriate up to
900oC. Water or dried water spots can interfere.
Performs poorly when paper has been wet
Develops prints on charred paper in laboratory
environment
Useful for areas where charring & soot deposits:
Use view finder of IR Camera. Use lens filter
>715nm – RG850 filter.
Good up to 200 oC
Stops working >150oC