Impression Evidence
General & Scene Considerations
Overview
Impression Evidence
Anything that leaves an impression
can be compared with an original
 Class Characteristics
 Marks produced during manufacture AND during routine use
– Made during the manufacture of the tool or the object
Accidental or Unique Characteristics
 Small (or microscopic) unique (accidental) marks are thought to
be traceable to a specific object
 Occur during normal useage
Classifying Footwear Impressions
 Three categories:
 Visible: Occur after someone steps into a foreign
substance and then transfers the substance to a clean
surface.
 Depending upon the background color, a visible print
may be a simple impression made from dust on the sole
of the shoe.
 Plastic: Occur when someone steps into a malleable (soft)
surface and leaves a three-dimensional impression.
 Typically, this could be an impression in mud or
cement.
 Latent: Those that are invisible to the naked eye and
typically require an aided eye to make them visible.
General Characteristics of
Impression Evidence
2D Impressions
 Defined as a pattern lying ON TOP
of a surface
 Latent (invisible)
 Patent (visible). Examples are
fingerprints, footwear impressions
and tire tracks, among others.
 Dust impressions are usually
classified or defined as 2D impressions,
 Actually three dimensional having
very shallow depth and surface
topology
3D impressions
 Object impresses its
pattern into a softer surface,
 When tire makes
pattern in wet mud.
 The famous
impression of Neil
Armstrong’s footwear
impression on the moon
is an example of a 3D
impression
Impression Evidence
 Large, diverse group,
 Expect at least one category present at most scenes.
 Fingerprints – most prevalent
 Next would be footwear and tire impressions
 Bite marks (sexual assaults), lip prints and ear prints
comprise another category but occur much less frequently.
 Tool mark impressions is another large class of impression
evidence that comprises several subcategories:
 Screw drivers, saws, cutting tools (wire cutters) etc.
 Ballistics evidence:
 Bullet impressions,
 Cartridge case impressions, and marks made by other
Categories of Impression Evidence
Fingerprints
Footwear Prints
Tire Tracks
Tool Marks
Fired Weapon
Bullet Marks
Cartridge Cases
Bite Marks
Ear Prints
Impressed prints
Shape of a tool
Striated impressions or striated marks/scraping
marks
Scrapping of tool’s surface against receiving
surface
Footwear Impression Evidence
A Class of Associative Evidence


Refers to its future use; to help ascertain the truth of alleged facts.
Footwear evidence = Associative evidence.

Helps investigators (police and prosecutors) and juries support contention that
someone had been at crime scene.

Can identify which shoe left an impression ,,, can help place someone at the
scene. ….

Alone, not determinative of guilt,
 Help circumstantially toward that end.
 Thus finding footwear evidence linked to an individual shoe can be critical
evidence,
 Used by a prosecutor during trial.
 Also helpful for investigators to understand the veracity of witness or a
suspect’s statements.
 Locating footwear evidence: not easy … logic can point to the location where to
search.
 Time and effort spent locating, photographing, lifting and comparing impression
evidence is critically important.
National Research Council 2009 Report
 National Research Council of the National Academy of Sciences
suggests that pattern (impression) evidence should be interpreted more
carefully.
 The report says that additional research is necessary in order to
determine the underlying scientific basis of pattern evidence comparisons.
 NRC committee also suggested there should be a statistical basis for
making these comparisons, which currently, does not exist.
 Practitioners do not universally agree that a statistical basis is
necessary for making valid comparisons.
 The NRC report does not say or imply that footwear comparisons are not
valid nor does it say or imply that these comparisons have no forensic value.
Value of Impression Evidence
Links to Other Crimes
Minimum # of Perpetrators
Association with Other Evidence
Laboratory Examinations Establish Links
Database searching
Footwear impressions from various crimes
Useful for investigations of repetitive crimes
Burglaries
Recidivism rate is high >50%
Multiple impressions
Absence of multiple impressions
Suggests a lone perpetrator
Backtracking footwear impressions
Path of perpetrator
Discarded weapons or other evidence
Associate footwear with tire
impression - lead to a vehicle
Entering a House
From the Outside
Example
 Burglar enters a house
through a window and steps
onto a carpet,
 What is probability that
dirt residue from sole will
leave an impression?
Entry
Point 1
 Defines residue type on shoe.
 Subsequent steps transfers
residue from shoe to carpet.
 Forensic value not known until
found and evaluated.
Entry
Point 2
Hypothetical Murder Scene
 Assume two burglars enter scene at different points,
 Expect different footprints
 ‘Entry Points ‘1’ and ‘2’.
 If both footprints entering house at different locations had
the same sole pattern (class characteristics)
 Suggests @ least two people involved.
 Remote possibility that same person entered on
separate occasions.
o Close examination of the size and other
characteristics might dispel that argument.
 Using the same logic, suppose a third unknown fingerprint was
found inside the house.
 Suggests a third perpetrator.
Impression Evidence is
Commonly Overlooked
Why Impression Evidence Is
Overlooked or Not Found
1. Not aggressively looking for
Training
Belief can’t be found
Incomplete understanding of value
2. Incomplete search of scene
Inability to find points of exit/entrance
3. Lack of Understanding a Class of Fragile Evidence
4. Lack of knowledge of How to Collect and Preserve
Scene
Other
1. Weather Obliterates Outside Prints
2. Surface Characteristics not Conducive to
Production of Impression Evidence
3. Scene Entrance Only Access to Scene
1. Initial Scene Responder Obliterates
2. Public Obliterates Before Authorities Arrive
2D Impressions
Common but Overlooked
Types of 2D Impressions
Dry Residue
Impressions
Wet Residue
Impressions
Made from Dust
Made from a Wet Slurry
2-D Impressions
 Most found on floor
surfaces





Magazines/newspapers,
Tile floors
Dust prints on carpets
Shoe prints on doors
Stepped-in
grease/oil/blood
 Requires careful
inspection/search of
scene
 A category of fragile
evidence
 One of the first activities
 Impression transfers vary
 Clean shoes leave impressions on
paper/glass/countertops/furniture
 Dirt and/or dust
 Wet grass
 Grease, oil, wax or furniture polish
 Blood or other fluids.
 Visibility of an impression
 Contaminating material deposited
by shoe
 How it contrasts w/a surface
 All impressions are
potentially identifiable
 Often, less visible
impressions leave more
detail
Intellectual On-Scene
Impression Evidence Checklist
ALWAYS Expect Impression Evidence.
 Study the Scene!!!!!
 What is the likelihood of finding probative impressions?
 Where would they likely be?
 Are they wet or dry residue impressions
 Would they be plastic, latent, visible?
 What is the strategy for archiving?
 Is it necessary to enhance them?
 Can they be lifted?
 How should they be preserved?
Impression Prints @ Crime Scenes
Point of Occurrence
Areas of Struggle
Point of Entry/Egress
Path Through Scene
Spilled Blood
Victim’s Clothing
Furniture
Floors
Strewn reading material
Windows
Adjacent areas outside
Struggle-to-Victim to Exit Point
Other Footwear Patterns
On Doors – kicked in
Outside
Landscaping
Driveways
Walkways
Likelihood of Detecting
2D Footwear Patterns
Wet Shoe
Blood/oil/Grease
Dry w/Dust
Clean
Dry
Unlikely
Very Likely
Likely
Unlikely
Dirty floor
Likely
Very Likely
Unlikely
Unlikely
Clean unwaxed floor
Likely
Very Likely
Very Likely
Unlikely
Relatively clean unwaxed
Likely
Very Likely
Very Likely
Likely
Waxed desk top
Likely
Very Likely
Very Likely
Likely
Glass
Very Likely
Very Likely
Very Likely
Likely
Kicked in Door
Very Likely
Very Likely
Very Likely
Likely
Paper/cardboard
Very Likely
Very Likely
Very Likely
Likely
Surface
Carpet
Following Footprints
Through the Scene
Bodziak: Footwear Impression Evidence, 2nd Ed, CRC Press, New York
Using Technology
Finding Footwear Impressions
2D Impressions
Flashlight – Oblique Lighting
RUVIS
ALS
Oblique Lighting
Low angle light for impression evidence:
Wet & dry residue footwear prints, tool marks, fingerprints
Camera
Camera
Light source
Light source
3D Impression
Dry Residue Print
Wet & dry residue footwear prints, tool marks, fingerprints
The Mirror Technique
Enhancing & Archiving
Impressions
Composition of Dust and Soil
Dust – General Considerations:
 General term for solid particles with diameters less than 500
micrometers
 Comes from the atmosphere – sources include:





soil dust lifted up by wind,
pollution,
volcanic eruptions,
animals and
people.
House Dust
 Human environment, e.g.,
 Homes, offices, etc.,
 Contain human skin cells, bacteria, plant pollen, human and
animal hairs, feathers, textile fibers, paper fibers, minerals from
outdoor soil,
 Other materials,
 All come from the local habitat.
 The quantity and composition of house dust varies greatly with seasonal
and environmental factors:
 Surroundings,
 exchange of outside air,
 age of the house,
 building materials and their condition
 quantity of furniture and carpets,
 state of preservation.
 ventilation,
 heating/cooling systems and
 habits of those living in the house.
House Dust
 House dust consists of inorganic (minerals) and organic
matter,
 Relative proportions vary considerably.
 Dust from the homes with animals consists nearly
completely of organic material.
 In a study of 318 house samples, the proportion of
organic matter ranged between <5% to >95%.
 A survey of 11 homes showed
 Organic content of house dust ranged between 25.7% to
56.5%,
 Floor dust from seven offices had an organic fraction of
33%.
 Variances vastly different in different regions –
 North, south, east, midwest, southwest, west.
 Rural or urban.
Enhancing 2D Impressions - Overview
The Logic of Enhancing Impression Evidence
 Understand the likely content of
dust at scene
 Archive – Photography
 Determine type of Impression


Dry Residue Impressions



Electrostatic Lifter
Gel Lifter (Gellifter)
On paper
o
Chemistry (iron)
Wet Residue Impressions




Gel Lifter
Chemistry
o
o
o
Fe: Ammonium Thiocyanate
Fe/Mg: 8-hydroxyquinoline
Oils: Iodine/benzoflavone or starch
Dusting
o
Black magnetic dusting powder
Superglue fuming
The current paradigm for enhancing
dust impressions at crime scenes is
single dimensional … typically involves
lifting or chemical tests to visualize the
mineral content of the dust.
Sort of a crap shoot.
Electrostatic Lifting
 Apparatus that creates static electricity between dust
particles in the impression and a foil-backed Mylar film placed
over the impression. If the print lifts, it is a dry residue print.
That is, it was made from dust.
Foil (silver)
Side of Film
(up)
Electrodes
Footprint
in Dust
Electrostatic Lifter
Stun Gun
Foil-backed
Mylar Film
Black Side
of Mylar
Film (down)
Black Mylar Side
on Dust Print:
Foil Side Up.
Electrode touching
foil side
+
Ground Electrode
Arrows to Positive
& Negative
Electrodes
Mylar Sheet
Foil Side up
The set up
Fingerprint roller
To Flatten Mylar
Lifted Footwear Impression
Electrostatic Procedure
 Place the metalized lifting
film over the dust print. (dark
side down)
 Place the grounding plate
about 8” next to the film.
 Turn lifter so that the two
metal probes on the back
are resting on the grounding
plate and the single probe is
resting on the film.
 Turn on the device and the
film will be sucked down
onto the print.
 Gently brush over the film to
remove any air bubbles.
 Lift and you have your dust
print.
Effects of Humidity and Temperature
 The issue of humidity studied by investigators employing a similar technique ESDA
for the detection of indented writing.
 Studies show >>> humidity necessary … becomes detrimental when the relative
humidity goes above 98% at room temperature … quality drops off.
 At cold temperatures, even lower humidity causes a decrease in the quality of the
highlighted indented printing.
 ESDA is not an electrostatic lifter, but the principle is the same, and one might expect
similar deterioration of the quality of prints using an electrostatic lifter.
 Generally, normal use of electrostatic lifter under normal conditions of temperature
and humidity should provide reliable results.
 HOWEVER … absence of humidity … ESDA process requires humidity … opens the
possibility that the absence or near absence of humidity may also affect the quality of
electrostatic lifts.
Electrostatic detection apparatus (ESDA)
ESDA stands for Electrostatic Detection Apparatus. Used to produce a permanent 'lift'
from paper which provides a visual map of indented impressions
 Non-destructive. The paper under examination remains in exactly the same state,
still available for other examinations.
 Extremely sensitive - indentations found up to seven sheets below the page where
the original writing was made.
 ESDA works by stretching a Mylar film (like Clingfilm) over the document being
examined.
 Mylar film is electrostaticaly charged.
 Where the paper is smooth, charging is generally uniform, however where
the fibers of the paper have been disturbed by paper-paper contact caused by
indentations, the electrostatic charge is different versus the background.
 Creates latent image. In order to visualize this latent image, Black toner
similar to that used in laser printers is applied to the surface of the Mylar.
 Toner preferentially sticks where the electrostatic charge congregates
 Areas of the indentations … an image with a grey toner background and
darker toner traces in the areas where there are indented impressions.
 Image is made permanent as a 'lift' by placing clear 'sticky backed plastic'
over
 Variables: Type of paper, the type of pen or stylus used, the number
of sheets of paper between the writing and the sheet holding the
impressions, the humidity at the time the impressions were made, the
humidity at the time the ESDA lift was made, the method by which the
toner is put onto the Mylar film*, and the amount and direction of the
electrostatic charge put onto the Mylar film.
 Not suitable for the examination of loose fibred paper such as newspaper or very
glossy paper such as magazine covers.
 Liquid will completely destroy the ESDA impression. … fingerprint treatment
should be done AFTER any ESDA examination.
 Toner can be put onto the Mylar film using three methods: cascading tiny glass
beads coated with toner over the surface, puffing an aerosol of toner powder over the
surface or using a device similar to a powder puff to apply the toner.
Storing Electrostatic lifts
 Electrostatic lifts - fragile and must be protected.
 Storing in flat boxes preserves better than other methods:
 Do not roll in tubes.
 A problem with flat storage is that dust is attracted to surface because the
lift retains a residual static charge – it stops the dust from falling off the
Mylar film.
 Problem exacerbated when lifts exposed to open air or in low-grade
cardboard.
 Even lifts stored in a high quality cardboard will lose residual charge over
time resulting in the complete loss of the impression.
 Storage conditions:
 High humidity increases rate of residual charge degradation
 Store with a desiccant (silica gel) taped to inside of box.
 Recommended to store the lifts so that the humidity does not exceed
50%.
Differentiating Dry
& Wet Residue 2D Impressions
Impression at Scene
Photograph
Electrostatic Lift
Dry Residue Impression
 If the print does not lift, it is a
wet residue print.
 Advantage of
electrostatic lifting is
preservation of the
impression detail onto a
black, Mylar surface.
 What if, however, the
impression does not lift? Is that
proof that the impression was
formed from a wet shoe?
Wet Residue Impression
Photograph
Enhance
Preserve
Impression
Protect in Lift Box
Protect with Gel Lifter
Magnetic
Powder
Chemical
Enhancement
Photograph
Powder
Suspension
Gelatin Lifters (gellifters)
For preservation purposes, they serve a
similar function as electrostatic lifters
 Effective multi-tasking tools.
 Commercially available in two forms:
 Rubber-backed gelatin-based in black, white or
 Clear gelatin on a clear backing.
 Semi-sticky surface lifts dry residue impressions AND
wet residue impression.
 Not reliable for differentiating between dry and wet
residue impressions.
 Do not require static charge.
 “Sticky” surface “grabs” dust impression and sticks it
to the surface of lifter.
 Also pick up any surrounding, contaminating material
such as dust, which can mask the lifted impression.
Black Gellifter Lifting
Footwear Impression
Gelatin Lifters (gellifters)
 For dry residue prints, the light tan color of the impression is nicely off-set by the
black of the gellifter.
 Like electrostatic lifters, gellifters can lift impressions from hard surfaces, paper,
carpeting, clothing, etc.
 They are particularly useful on vertical surfaces.
 Storage:
 In uncovered high quality cardboard boxes works well.
 Generally recommended that low grade cardboard boxes not be used
because … tend to shed fibers onto the lifted image.
 Also, breathable boxes will keep condensation from forming on the lifts.
 Remove acetate sheet that comes with the lifter
 Removing it later can remove some of the image.
 Store the lifts in the same way as electrostatic lifts: high grade cardboard box
without the acetate cover.
 Over dusted or dense dust impressions can benefit from repeated removal of the
acetate cover because this tends to remove some of the excess dust and render the
lifted impression sharper.
Gellifter Type
Black
Characteristics
Possible Uses 20
Jet-black color and the high-gloss finish.
The high-gloss provides for a reflection of
light from the illumination source. Any light
not reflected by the gelatin layer will be
absorbed.
-Footwear impression lifts
-Fingerprint developed with:
Powders
Superglue
SPR
-Fingerprints on some adhesive sides
-Postmortem fingerprinting
-Fingerprints on latex gloves
-Improving old fingerprints
Traces picked up by the Gellifter, however,
will reflect the light in all directions. The
end result is a high contrast between the
lifted material and the gelatin layer. Black
fingerprint powders, lifted with a black
Gellifter yield images that are sharp and
rich in contrast.
The gelatin layer of the white Gellifter
absorbs blood and dyes from staining
solutions.
White
Clear
The extreme white color of this Gellifter
has a low fluorescence. Staining solutions
which fluoresce when excited with green
light (e.g., Hungarian Red) will therefore
show up in high contrast to the gelatin
layer.
The transparent Gellifters have a clear
polyester backing
-Fingerprints in traces of blood and
traces in blood after chemical
treatment
-Fingerprints in staining solutions
-Muddy shoeprints on nonporous
surfaces stained with safranine O
-Improving old fingerprints
-Fingerprints developed using
powders – forms a positive print
-Exemplar footwear impressions
Adapted from the BVDA gellifter brochure: http://www.bvda.com/EN/download/Gellifter_brochure.pdf,
Chemical Enhancements of 2D Impressions
Dry Residue Prints
Dust or Dirt?
 8-hydroxyquinoline
 Fluorescent reaction with iron, aluminum and
magnesium.
 Spraying the reagent in the dark (outside this is
difficult) gives yellow-white fluorescence that
must be photographed immediately.
 Testing the background before spraying the
impression is critical
 Testing a small part of the impression to see if
the reagent is going to react with the dust/dirt
present.
8-Hydroxyquinoline – UV Light
Chemical Enhancements
of 2D Impressions
Bromophenol Blue
and Bromocresol Green Chemical
Reagents
Before Enhancement
After Enhancement
After Water Vapor Treatment
Journal of Forensic Sciences, JFSCA, Vol.
41, No. 1, January 1996, pp. 23-26.
Oil or Fats
Iodine fuming
 Iodine fuming followed by development with 7,8-benzophenone gives
a blue/purple color.
 First test a small part of impression and surface to see if the iodine is
reacting.
 Not a chemical reaction that takes place but more of an incorporation
of the iodine into the matrix of the oil/fat.
Another way to visualize an iodine infused impression is to dust it with
cornstarch and then hold a steam iron over the impression. The iodine
will react with the starch to form a dark blue color.
Salt
In the winter, tires running over roads salted with NaCl (sodium
chloride) will have the salt on the tread.
 Transferred to a surface over which the vehicle travels. Spraying the
impression with Silver Nitrate (AgNO3) will form silver chloride (AgCl) in
those areas of the impression containing sodium chloride.
Shining a UV light or allowing sunlight to bake the impression will
convert the AgCl to metallic Silver (Ago), which will appear dark gray or
Using Photography to Enhance
 Photographic sequence
important
 Establishing (
 Midrange
 Close-ups (examination quality or
1:1)
 Record detail
 With & without scale – In the same
plane
 Need to make 1:1 enlargements
 Next to & parallel to print @ same
level as impression
 Made in plane of impression (vertical to
impression)
 Tripod is essential
 Appropriate lighting
 Oblique
 ALS
 RUVIS
Camera Setup
http://site.utah.gov/dps/impressions-fw-evidencecollection_000.htm
Photographing Footwear Impression Evidence
 Examination quality photographs should always be taken of both twodimensional and three-dimensional footwear impressions
 Photographs are taken for later comparison with known footwear
 A PROPER scale should ALWAYS be used when photographing
footwear impressions
 The scale should be on the same plane as the impression
 Objects with impressions should be removed from the scene if possible,
AFTER examination quality photograph taken
 Always use a tri-pod
 Fill the frame of photograph with your impression including your scale
 Shade impression in sunny conditions
 Use side lighting from different angles
take several shots
Proper Location of Light Source for 2-D Residue Prints
Light Source Should Be 4-5 Feet From Impression
From: Bodziak: Footwear Impression Evidence1
Existing Overhead
Lighting
Oblique Lighting
10 Degrees
Oblique Lighting
25Degrees
Ambient Light + External Source
From: Bodziak: Footwear Impression Evidence
Oblique Lighting
45 Degrees
High-Contrast
B/W Photography
Film cameras
 High-contrast B&W film
 Kodak Tech Pan
Digital Cameras
 Use B&W setting
 Use software to convert
color images
Filters
 Subtract out the
background
 Gray impression on red floor
 Use red filter on camera
 Use UV or IR light
 ALS
Cross Polarization
– Can Cut Glare
Polarizing filters can
enable impressions to be
photographed
 One filter in front of
oblique light source
 Other filter in front of
camera lens
 Rotate filters to achieve
max visibility of impression
 Important technique for
cutting glare
 UV wavelengths
 UV spectrum : 10-400nm
 Long-wave: 320-400
 Middle-range: 280-320
 Below 200: not useful
UV Light
 Use Reflected short-wave UV light - RUVIS
 18A filter over lens of camera
 Filters out visible entering camera but not UV
light
Unaided Eye
(Photos Rachel Leintz)
Long Wavelength UV Image
http://www.ultravioletcameras.com/pdf/ETM-LongwaveUV.pdf
IR Light
IR Spectrum
 Useful portion:
700-900nm
 Digital Camera
altered for IR
 Use tungsten light
source - strong IR
light
 Use #87 filter over
camera lens to
block all visible
light
Enhancement of Bloody Footwear Impressions Photography Using the ALS & Chemically
Bloody Print On Terracotta Tile
Photograph With Flashlight
Bloody Footprint Developed
with Amido Black Protein Stain
Some blood enhancement chemicals work on only nonpourous surfaces (amido black), pourous surfaces
(hungarian red), and some will work on both pourous and
non-pourous (LCV). Once impression photographed, it can
be collected.
Photograph using ALS @ 535nm
This can be done by submitting the entire piece it was left
on, or a gel lift can be used.
http://site.utah.gov/dps/impressions-fw-evidencecollection_000.htm
Choosing a Method for Enhancing
Lots of Choices
 Need to understand the surface ,
 How the method works
 Method’s limitations
Static
Lift*
Gel
Lift*
VWD
SG/BY40
Mag.
Black
Aluminum
Black
Powder
Powder
Suspension**
----
+
++
----
----
----
++
++
Soil – Loam
+
+
++
----
----
----
----
++++
Soil – Chalk
+++
+++
++
----
----
----
++
++
Grass Stain
----
+
++
----
----
----
++
++++
Engine Oil
----
++
++++
++++
++++
++
----
++
WD40
----
++
++
++++
++++
++++
++++
++
Baby Oil
----
++
++
++++
++++
++
++
----
Kitchen Fat
----
++
++++
++++
++++
++++
++++
++++
Diesel Fuel
----
++
++
+++
++
++
++
----
Detergent
----
++
++++
++++
++++
++++
++++
++++
Dish Soap
----
++
++
++++
++++
++++
++++
++
Sprite
----
++
++
++
++
++
++++
++++
Diet Coke
----
++
++
++
----
----
++
++
Milk
----
++
++++
++++
++++
++
++++
++++
Beer
----
++
++
++
++
----
----
++++
Cider
----
++
++
++
++
++
++
++++
Dusty
++++
++++
++++
----
----
----
----
----
Soil - Clay
Wet Residue Prints
Made from wet shoes/boots
Enhancing depends on
 Chemistry of recipient surface
 Chemistry of the impression
 Preservation technique
Powder Dusting Wet Residue Footwear Impression
Fingerprint powder (magnetic powder), can be used for collecting footwear evidence of WET ORIGIN. A wet origin
impression is made when a wet shoe with dirt and debris walks across a solid surface such as tile or a wood
floor. After drying, the dried impression is left. Use oblique lighting to find impressions.
http://site.utah.gov/dps/impressions-fw-evidencecollection_000.htm
Lifting Dusted Impression With White Gellifter
http://site.utah.gov/dps/impressions-fw-evidencecollection_000.htm
Chemical Methods
Because of soil components, we can enhance
footwear Impressions chemically.
 Best and most logical approach
 Employ Chemistry in the laboratory instead of at scene.
 However, some scene circumstances may dictate chemical
enhancement @ scene.
 The result is either a colored or fluorescent impression, which can
be photographed easily.
Enhancing Wet Residue Prints
Technique
Ammonium or Potassium
Thiocyanate
8-hydroxyquinoline
DFO
Analyte
Tested
Procedure
Fe
Spray
Red-Brown
Fe, Ca, Al, others
Spray
Fluorescence under
UV light
Treat gel-lifted surface
@ 95oC
Fluorescence @ 515535nm
Amino
Acids/Protein
s
Result
Expected
Safranin O
Oils
Treat gel-lifted surface
Fluorescence @
535nm
Iodine
Oils
Fume in humidity
followed by a
benzophenone
soak
Blue/purple
pH of impression
CaCO3
Superglue fuming
Nucleophilic
species
Spray or soak
Fume after
humidifying
impression
Blue
Dust or stain
developed
impression
Chemical Checklist
 Checklist: Choosing method depends on following:
 Chemistry of the recipient surface.
 Chemistry of the impression
 Preservation technique
 The chemistry of the surface critical to successful enhancement.
 If impression lies on a linoleum floor and the only resource is 8hydroxyquinoline, always the possibility that the surface will react with the
reagent
 Will mask the fluorescence of the impression.
 Check chemistry of the surface first - ensure that it does not react with
reagent.
 The chemistry of the impression also critical
 Before treating impression determine whether the components in the
impression are going to react with the reagent and give the expected color or
fluorescence.
Preserving 2D Wet Residue Prints
 Print dusted with magnetic powder
 Gel Lifted with White Gellifter
Alternative techniques
 Powder Suspension (WetWop – Iron Oxide)
 Iodine + benzophenone
 Iodine/starch
 Magnetic Powder
Bloody Footwear Impressions
OJ Simpson Murder Case - 1994
http://www.members.tripod.com/~VanessaWest/nsimpson2.jpg