Fingerprints Part II

Part IV
Print Development Methods
Fingerprints and DNA
DNA from fingerprints.
For DNA analysis to be successful, try to collect at least 100pg of DNA
Each cell has about 6pg
Need about 100/6 = 16 cells
Most fingerprints have < 100pg
Only about 20% of fingerprints have sufficient amounts of DNA
Fingerprints and DNA
Create Secondary Powder Source by removing
Powder from original container to secondary container
British studied powder dusting on
ability to obtain usable DNA profiles.
Take Powder from
Secondary Source
 Lifting using traditional lifting
methods – tape and gels - does not
quantitatively capture the DNA.
 After lifting, swab lifted area
Original Powder Source
 to collect remaining cellular
Secondary Powder Source
 Can still get DNA profiles using
sensitive DNA analysis techniques from
lift and swabs taken from the lifted area.
 Probably no relationship between
Slim possibility of contaminating a
amount of fingerprint residue present
fingerprint’s DNA with another after using
and amount of DNA present.
the same brush and powder …
 Related to a person’s ability to
shed cellular material.
Use clean brushes and fresh powder
 Referred to as shedders
between dusting.
Do not mix used and fresh dusting powder
by releasing the used powder into the
original reservoir.
Specialized Physical Methods
Wet/dry Surfaces
Small Particle Reagent (SPR)
Suspension of molybdenum sulfide grains
 Size of crystalline particles is critical
 In mild detergent solution (Kodak
Photoflo or 1 drop of Dawn in
 Alternatives to molybdenum
Iron oxide
Zinc carbonate
employed with varying success
Two fingerprints on a car, developed with SPR.
tried on dark surfaces (particle size
 Some fluorescent compounds,
well on non-porous dry surfaces
Plastic bags/wax paper/glass/painted
surfaces/water-soaked firearms
Adheres to fatty components of latent
Used in a sequence approach
Used for items cannot be dried prior to processing
Useful for sticky-side development
Vacuum Methods
Vacuum Methods
Vacuum metal deposition (VMD) – Columnar Thin Films (CTF)
Smooth nonporous surfaces
 Plastic bags/plastic packaging
material/smooth surfaces
 Drawbacks
Equipment is expensive
Sample chamber is small
 VMD - Evaporates Gold and
then Cd or Zn in vacuum
How VMD Works
Fingerprint ridge
Vacuum Deposited Gold
Thin metal film deposited onto
CTF – Can work with other
methods – Superglue fuming
Vacuum Deposited Zinc or Cadmium
Columnar Thin Film (CTF) Development
A Measure of Topology
Developed in 2009
Lahktakia & Shaler
Columnar Thin Films of Deposition
Material onto Fingerprint residue
 Thermal Evaporation of Deposition
Chalcogenide glass
AlQ3 – fluorescent
Tops of Columnar Columns
Looking Down on CTF Ridge
Fingerprint Ridge
Superglue Fuming
Requires Active Chemical Molecules in Print Residue
Amino Acids
Superglue Fuming
Two methods
Heat & Humidity vaporization of superglue
 Vacuum vaporization of superglue
Heat & Humidity
Super Glue Fuming
Heat & Humidity
80% Humidity
Microburst Method of FBI
Fresh Oily Print
2-Day Oily Print
A: Image of a fresh, cyanoacrylate fumed oily print at a 5000~
B: SEM image of a cyanoacrylate fumed two-day-old oily print at a
5000~ magnification.
Vacuum Superglue Fuming
Developed Watkin & Misner 1990
Nat’l Res. Council of Canada
Large metal chamber with object to be
Pressure reduced to 200 mtorr (0.2
With small quantity of superglue
Std atmospheric pressure is @ 760 torr
Accelerates vaporization of superglue
Reduces time to deposit reduced about
20 min.
Prints translucent – weakly
Sharper ridge detail & more pore detail
More uniform prints
Less risk of overdevelopment
Vaporization can be used to develop
prints not directly exposed
Inside of plastic bags
Not applicable to:
Cans/bottles because they may explode
Nothing wet
Visualizing Superglue Prints
 Super Glue Polymer has no significant
absorption band
 Visualizing Superglue Prints
 Depends on color of object
Choose opposite to color of
exhibit’s surface
Using Light
 White light or 450nm for
initial examination
• May need oblique
Reflective UV light
• Light ridges against dark
Staining – fluorescent dyes
Dusting – various powders
SceneScope - imager uses
intensified UV reflectance instead
of fluorescence
 Not an ALS (Alternate light
Detects fingerprints (and footwear
impressions) on most non-porous
surfaces prior to any treatment or
after cyanoacrylate fuming.
Visualizing Superglue Fumed Prints
Enhancement with Fluorescent Stains
Solvent for fluorescent stain is
Must soften the polymer
Water rinse after staining
Preferred for
Rhodamine 6G
Ardrox 970-P10
Basic yellow 40
Mixtures of Dyes for colored
Non-luminescent surfaces
Dark and/or multicolored
Most popular Dyes
Allows penetration of stain without
damaging the print image
Not suitable for:
Porous surfaces
Semi-porous surfaces
Adhesive Tapes
Always Assume
Prints present on smooth AND the sticky-sides.
Tapes are important because routinely used to seal boxes, letters and packaging.
Also used to restrain people.
 Two distinct surfaces, each with unique development issues.
Easy for fingers to stick to sticky side of tape - print impression transferred to tape.
Latent print can be on smooth side of the tape.
 Developing fingerprints on the sticky-side of tapes has presented developmental problems.
Traditional dusting powder does not work because it sticks to the adhesive and masks prints that might
be present.
 Scientists and investigators developed variety of methods for developing adhesive-side prints.
Must determine chemistry of sticky-side of tapes
Affects subsequent print development.
Rule of thumb
 Tapes should be collected … preserved … taken to laboratory for print development …
especially if tape stuck to itself.
Rare instances when this is impossible
Un-sticking tape and developing the prints on-scene is necessary.
Adhesive Side Print Development
 Several techniques available or sticky-side of tapes:
 Small Particle Reagent (SPR),
 Black and white WetWop,
 Sticky-side powder,
 TapeGloTM ,
 TapeGlo is a fluorescent dye
 Gentian violet,
 Gentian violet (Basic Yellow 3): stains fats.
 Iron oxide powder-based suspension and others
 Powder-based suspensions in a dilute detergent
No Technique develops prints on all adhesives all of
the time
Tape adhesives categorized: Rubber or acrylic-based
 Chemically, adhesives differ … why powder suspensions and
chemical formulation development techniques work with one type
of tape and not another.
 Masking tape represents a third category … Porosity creates
problems for print development.
Spot Testing Adhesives
 Apply a toothpick-sized but clear spot of black or white powder
suspension to a section of the tape that is less likely to have been
 Wash the spot and only that area of the tape with tap water
until the excess powder is gone.
 If powder remains on the spot, the adhesive is PROBABLY
acrylic-based and should be developed using an aqueous version of
Basic Violet 3 (Gentian Violet).
 If the tape is visible through after washing the test spot, it is
probably a rubber-based adhesive and should be developed using
Tapes – Sticky Side
 Rubber-based
adhesives –
 Use powder
Iron Oxide suspension
 Acrylic-based
adhesives –
 Basic Violet 3
 TapeGlo™ :
 A fluorescent dye.
 Contains no hazardous or
flammable liquids
No fume hood is required
Shelf life is approximately six
 Pour TapeGlo™ into a
dipping tray or spray on the
adhesive surface.
 Fluoresces best when
viewed between 488nm
and 540nm.
Removing Tape from its Substrate
Physical processes.
Pulling apart:
Fastest method … causes least damage to the underlying prints. Tedious and there is always
the possibility of distorting the tape … alter underlying prints if surfaces – tape and surface – are tightly
Not recommended without a good reason.
Cooling (Freezer)
Many recommend cooling to un-stick from surfaces OR to un-stick them from themselves.
… Freezing using liquid nitrogen or a microcircuit freezing spray. … Cool below the adhesive’s
critical ‘glass transition temperature.’ … liquid nitrogen … dry ice. Adhesive solidifies … gently
and slowly pulled from the surface or from the sticky-side of an adhering adhesive.
Essentially the frozen adhesive ‘fractures’ from the surface to which it is bound.
Freezer Spray
Tantamount to freezing. Electronics industry use these sprays … replace liquid nitrogen for
separating adhesives from various surfaces … except from other adhesives. Temperature in
the -65oF range, so precautions are necessary: wearing appropriate PPE: gloves, face mask,
protective clothing.
Hydrocarbon-based solvents recommended for adhesives stuck to other adhesives:
UnDoTM. Slow and tedious … use tiny amounts of solvent because too much will dissolve the
adhesive and ruin prints.
Freezer Spray
 For localized, small areas of tape.
 Method of choice for removing
adhesive tapes from plastic bags and
other plastic material.
 Will freeze skin – use thermal
 Not for removing adhesive from
paper, cardboard or from adhesives
adhering to adhesives.
 Solvents:
 Removing adhesives from
adhesives using solvents should be
done carefully.
 Alternative method for
disengaging adhesives from paper
and cardboard and for separating
adhesives from adhesives.
Super Glue for Adhesive
Low-level fuming
Fluorescent staining
Basic Yellow 40 staining
An alternate for gentian
SPR after SG fuming
Powder dusting
Sticky-side Development
Variable success
Type of tape
Consistency of the
Easily overdeveloped
Loss of print detail & poor
 Super glue fume prints on the smooth
side of tape before working on the
adhesive side.
 Fingerprints on smooth side
destroyed during cooling with
Freezer Spray by condensation
 Super glue fuming can develop
prints on both the smooth and
adhesive side of tapes.
 After developing smooth-side with
superglue, photograph then lift
 Then use freezer spray.
Enhancing Bloody
Special Situations
Bloody Fingerprints
 Considerations
How fingerprint made:
Contaminated with blood or already on surface developed by
the blood
o Positive or negative print?
o Pre-existing sebaceous prints repel blood
o Sebaceous (greasy) print
 Blood repelled by ridges & accumulates in furrows
Ridge detail may not be sufficiently defined for
 Use protein stain reagent
o Most do not interfere with DNA
Bloody Fingerprints
Chemical Enhancement – Protein Staining
Sprayed or squirted from wash
bottle or immersion
May require de-staining using
organic solvents
Protein staining reagents
Amido Black 10B (Naphthol blue
black B)
Coomassie Blue R250
Organic formulation
o Immersion 30 seconds
o Washing in organic solvents
o Ethanol/water wash solution
is field useable
o Blue/black stains
Aqueous formulation
Less hazardous
Can be used with gel lifters after
impregnating with dye
Possible alternatives
Acid Violet 17 (coomassie brilliant
Benzoxanthene yellow
(luminescence in weak blood)
Bloody fingerprint
photographed on human
skin with the aid of an
alternate light source.
Sequence Detection
Prints in Blood
Dark or Shiny
Observe via
Diffused reflection
Observe via
Absorption (415nm)
Visible as light ridges
Against dk. bkgrnd
Visible as dark ridges
Against light Bkgrnd
Examine in
Luminescence Mode
Protein Stain
Acid Violet 17 or Amido Black
Partial Bloody Print Developed with
Crystal Violet (left) & CTF ®
Partial Bloody Print Developed
with Coomassie Blue

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