Lesson 6 - Latent Print Development

Deposition Factors

Pre-transfer conditions
Transfer conditions
Post-transfer conditions (environmental factors)

Pre-transfer conditions

condition/health of donor’s friction ridge skin
amount and type of residue on skin

Transfer conditions

surface conditions (texture, surface area, curvature or shape, temperature, condensation, contaminants, residues)
pressure applied during contact, including lateral force

Post-transfer conditions

physical contact from another surface
water, humidity, temperature

Things to consider

residue (matrix)
surface (substrate)

sequential processing
co-assignments

Type of Print

Plastic
Patent
Latent

Plastic print

impression deposited in material that retains the shape of the ridge detail

Patent print

impression caused by transfer of foreign material on the finger to the surface and is visible to the human eye

Latent print

chance impression caused by friction ridge skin coming into contact with a surface

often natural sweat/oil
usually not visible to human eye
most common type of print evidence
requires optical, chemical, or physical treatment for visualization

Latent print residue

mixture of eccrine & sebaceous material
water soluble- amino acids
water insoluble-proteins and fatty acids

Substrate/surface

type (porous, non-porous, semi-porous)
texture (rough, smooth, curved)
condition (clean, dry, wet, tacky, sticky)

Correct order for sequential processing

liquid free processes used first
organic solvent-based processes used before water-based processes
water based processes should be used last

Types of examinations

Visual (optical)
physical
chemical

Visual examination

process where principal interaction results in the visualization of ridge detail is influenced by optical properties f ridge detail and the surface (white light, IR, UV, fluorescent)

Physical examination

process where principal interaction results in visualization of ridge detail is physical in nature (adhesion powder)

Chemical Examination

process where principal interaction results in visualization of ridge detail is chemical in nature (chemical reaction or staining)

Non-porous processes

cyanoacrylate
powder
dye stains

Equipment needed for CA fuming

secure fuming chamber/vacuum chamber
heating element
aluminum dish
humidity
cyanoacrylate ester

3 stage process to produce polymer growth for CA fuming

fumes of CA ester monomers are introduced to latent prints & quickly bond with residue
monomer on the residue reacts with another CA monomer to form a dimer and reaction continues forming a polymer chain of CA molecules
polymer chain reaction is terminated

Powders

considered physical process

essential elements
1) pigment: visualization, contrast to background
2) binder: adhesion to residue
photograph prior to lifting
label lift with location

Dye stains

considered chemical process
fluorescent process used after CA fuming
applied by dipping or spraying
dye molecules stick to CA polymer
developed impressions must be photographed using proper wavelength & filter
test prior to use

Porous processing

Indanedione
Ninhydrin

Indanedione

considered chemical process
close analog of ninhydrin
reacts with amino acids
results in faint pink color that fluoresces
100 degrees C and 60% humidity
fluoresces 520nm green illumination
590nm red filter

Ninhydrin

considered chemical process
nonspecific amino acid reagent
crystalline solid (pale yellow)
reacts with amino acids to produce ammonium salt
80 degrees C and 65% humidity
applied by dipping or spraying

Adhesive surfaces

Wet powder
Dye stains
Gentian violet
Fluorescent gentian violet

Wet Powder (sticky side powder)

considered physical process
powder suspension

adheres to and discolors ridge detail
can be used on adhesive and non-adhesive sides
applied by brushing onto surface using camel hair brushing and rinsing off after 15-30 seconds
not glued prior to use

Dye Stains

can be used on adhesive & non-adhesive sides
requires gluing first
dye stain on adhesive side can cause adhesive to dissolve or become sticky

Gentian violet

considered chemical process
aka crystal violet
stain that reacts with epithelial cells
highly sensitive
can be used on both adhesive and non-adhesive sides
works well on light colored substrates
applied by brushing onto surface or immersing item in stain for 30 seconds and then rinse

Fluorescent gentian violet

considered chemical process
gentian violet with fluorescent dye
stains epithelial cells
works well on dark colored surfaces
viewed under 525-570nm light source with red filter or 450-485nm using orange filter
applied 30 secs by brushing or immersing then rinsing off

Blood reagents

Acid yellow
Amdio black
Leucocrystal violet
Ninhydrin

Acid yellow

considered chemical process
blood processing technique for non-porous surfaces
binds to proteins in blood
works well on dark colored substrates
stains blood yellow
fluoresces 400-490nm wavelength & yellow/orange filter
fixing, staining, rinsing

Amido black

considered chemical process
aka naphthalene black 10B or acid black
reacts with proteins in blood
stains impressions blue color
works well on light colored surfaces
fixing, staining, rinsing

Leucocrystal violet

considered chemical process
catalytic test for blood
reacts with heme group in blood which produces violet color
requires hydrogen peroxide
presumptive test for blood
reduced colorless form of crystal violet
no fixative needed
spray on surface for best results
on porous and non-porous surfaces

Ninhydrin for blood

reacts with amino acids that make up proteins
works really well on blood

Untreated latent prints

blood
ALS (420nm): blood will appear darker
UV (365nm): blood will appear darker
IR (740-940nm): blood on dark colored fabric- blood will appear dark and fabric will appear light

Visible Light

light falls onto surface, light is absorbed and reflected
using fluorescence to view print- viewing or barrier filter blocks reflected wavelengths of light from light source while allowing fluorescent wavelengths to pass through

Small particle reagent (SPR)

considered chemical process
molybdenum disulfide suspension (fine powder suspended in a detergent solution)
effective on wet surfaces
works on non-porous surfaces that were wet at time of or after deposition
LP residue often lipid based when water is involved (SPR) adheres to lipids
sprayed onto surface for 1 minute then washed

Sudan black

considered chemical process
lipid dye; stains fatty components of sebaceous secretions, greases & oils
impression stained dark blue color
works well on surfaces contaminated with greasy/sticky substances
best on non-porous surfaces
used on waxy surfaces (candles, wax paper) can be used after CA fuming
soak for 2-3 minutes then rinse

Thermal paper

contains thermally activated layer
ninhydrin or indanedione blotter method
(soak blotter sheets/filter paper in reagent & place item between papers, place in zip lock bag & seal, cover with heavy items like books, leave for at least 48 hours)
include test strip to monitor or development
can remove thermal coating layer prior to/after processing (wash with acetone)

Adhesive removal

Un-du
label remover
used to remove labels/stamps from paper
Freezer spray/liquid nitrogen
used to separate layers of tape (adhesive stuck to non-adhesive)

Controls

Reagent prep:
stock & work solutions tested
include date, initials, & result(+)
log reviewed by different individual-date & initial

Reagent use:
working solutions tested at least once/day when used
CA must be tested concurrently
documentation of testing appears in case notes with +, date & lot #
expired reagent can be used if passes acceptable criteria during performance check prior to use in casework