Exam Flashcards
Porous Processing Sequence
Visual examination
Indanedione
DFO
Ninhydrin
(Oil Red O if wetted)
Physical developer
Porous Surfaces
Absorbent, permeable to gases or liquids, water will be absorbed
Examples of porous surfaces
Paper, cardboard, unfinished woods
Non-Porous Surfaces
Non-absorbent, not permeable to liquid or gas, water will pour off
Examples of non-porous surfaces
Glass, plastic, metal
What kind of chemicals need to be used to examine porous surfaces?
Chemicals that react to amino acids or chemicals that are sensitive to lipids and oils from fingerprint residues
Amino Acid
Organic compounds that combine to form proteins
Urea
An organic compound essential for waste production by the body after metabolizing protein
Sodium Chloride
Natural occurring salt in the body
Lipids
Organic compounds not soluble in water but soluble in fat solvents such as alcohol. Energy reserves that are also important components of cell membranes.
Drying Fingerprints
Most of the print is water, which evaporates and leaves lipids, amino acids, sodium chloride, and urea
Amino Acids on Porous Surfaces
Bind to fibres, making them stable even when deepened
What kind of chemical treatments react to amino acids?
Most of them
What are the factors affecting how deep a latent print will penetrate a porous surface?
Environmental conditions such as moisture/humidity, and the porosity of the surface
How are aqueous fingerprint reagents applied?
Dipping, spraying, or brushing
What does the choice of reagent depend on?
Colour, has the substrate ever been wet, porosity of the substrate
What happens with latent prints on non-porous surfaces?
Latent print resides on the surface
Semi-Porous Surfaces
Allow certain liquids or gases through, usually by diffusion
Examples of semi-porous surfaces
Magazines, waxy-coated paper products, carbon paper, photographs, glossy wall paints, wallpapers, latex gloves, varnished woods
Destruction of exposed prints on non-porous surfaces
Easily destroyed by rubbing when places in plastic bags, so use paper. Fragile against the environmental conditions.
Benefits of Indanedione
Reacts with different amino acids than ninhydrin and develops more latent prints than ninhydrin or DFO alone. Fingermarks are both visible and fluorescent, and more fluorescent than using DFO.
Indanedione Signature
Light pink colour under ambient light
Disadvantage of Indanedione
May be possible to degrade/destroy DNA so must test for DNA prior to using
Zinc Salts in Indanedione
Enhances colour and luminescence, with the only drawback being a reduced shelf life
Application of Indanedione
Liquid is applied to substrate and allowed to dry. Heat press at 165°C for 10 seconds, or incubated at 100°C for 20 mins at 60-80% humidity.
DFO
Amino acid-sensitive reagent best viewed with ALS
Benefits of DFO
Highly fluorescent, develops twice as many prints as ninhydrin
DFO Signature
Pale purple colour
Application of DFO
Liquid is applied to substrate. Heat in incubator at 100°C for 20 mins.
Disadvantages of DFO
Must be completed in a dry environment
Ninhydrin
Water and alcohol soluble. Reacts with proteins and non-specific amino acids, proteins, and peptides
Ninhydrin Signature
Ruhemann’s purple colour
Application of Ninhydrin
Apply liquid to substrate. Moisture and heat in ninhydrin cabinet.
Disadvantages of Ninhydrin
Requires a carrier solution or polar solvent
Benefits of Ninhydrin
Works well on older latent prints
What if you have multiple items from the same scene that need to be examined the same way?
They can be treated as a group (can all go in the cabinet together), but must be examined individually
Sequential Processing
A process used to examine an item in a methodical and systematic approach
First 3 steps of sequential processing
Same in each examination. Visual examination in ambient light, then white light, then a forensic light source.
What’s wrong with terms like “decision” and “likelihood”?
Uncertainty
Identification according to CanFRWG
Identification is the opinion by the examiner, based on training, knowledge, and experience, that the friction ridge impression originated from the same source
“Uniqueness”
Misleading or confusing in court
What should you say instead of “sufficient uniqueness to individualize”?
“Friction ridge identification is established through the agreement of sufficient friction ridge formations in sequence”
Filters
Can be used to enhance an image or eliminate other areas of the image. Allows specific wavelengths to be recorded.
2 Common Filters
Barrier filter and bypass filter
Barrier Filter
Suppress/block/absorb certain wavelengths and permit certain ones to help eliminate backgrounds. Blocks reflected light and transmits fluorescent light.
Bypass Filter
Allows a limited range of wavelengths to be recorded and blocks all other colour. Used with UV to allow only the UV range of wavelength.
Electromagnetic Radiation (ER) / Electromagnetic Spectrum
Energy moving in a wave-like motion. Includes x-rays, UV radiation, visible light, IR radiation, thermal radiation, radio waves, and microwaves.
Red ER
700 nm, lower frequency, less energy
Blue ER
400 nm, higher frequency, more energy
3 Primary Characteristics of Light
Wavelength, frequency, speed
How fast does ER travel in a vacuum?
Speed of light (299,792,458 m/s)
Short Wavelength
High frequency, towards UV
Long Wavelength
Low frequency, towards IR
How are wavelengths measured?
Nanometres (nm)
Visible Light Range
400-700 nm
Near UV Range
300-400 nm
Near IR Range
700-1100 nm
What happens to ER when contacting a surface?
Reflected, absorbed, transmitted
Types of Reflected Light
Specular or diffused
Specular Reflected Light
Light strikes a smooth surface and reflects at the same angle and parallel
Diffused Reflected Light
Light strikes a rough/textured surface and is scattered and not parallel
Absorbed Light
Converts to heat or luminescence
Luminescence
Molecules or atoms are in an excited higher energy state
2 Types of Luminescence
Fluorescence and phosphorescence
Transmitted Light
When light passes through an object without getting reflected or absorbed
What happens to light that is incident on a glass surface?
It will be reflects at an angle equal to the angle of incidence and transmitted according to Snell’s Law. ~4% is reflected determined by the refractive index of glass. May cause light to change speed and direction.
Refractive Index
Degree to which light bends. Frequency does not change but wavelength does.
What is the basis of light filtration?
Refractive index
Stokes Shift
Fluorescing light has a longer wavelength than incident radiation
How long does fluorescence emission last?
About 1 second after emitting radiation is discontinued
How long does phosphorescence emission last?
Several seconds after emitting radiation is discontinued
Incandescence
When light is emitted from an object that has been heated. Glows when it’s hot.
Chemiluminescence
Chemical reaction to cause heat and make it glow
Fluorescence
Emission of light caused by the absorption of radiant energy from an external source. Emission of light continues on if the stimulus continues.
Phosphorescence
Emission of light caused by the absorption of radiant energy from an external source or stimulus. Emission of light continues after the stimulus has stopped.
Barrier Filter Use
Used to block reflected light and transmit the fluorescent light. Coloured to a specific wavelength.
What does LASER stand for?
Light Amplification by Stimulated Emission of Radiation
LASER as a Fluorescent Light Source
Device that produces a coherent wavelength of light. Forensics uses coherent lasers.
LASER Wavelength
Works on a single wavelength between 525-550 nm, usually monochromatic 532 nm for fingerprint development in forensic labs
What does LED stand for?
Light-Emitting Diode
Use of LED-Based Light Sources
Intense light source, limited wavelengths for forensic use, fixed/non-tuneable wavelength, laser and ALS complement each other
How are ninhydrin prints enhanced?
With metal salt treatments. Silver nitrate turns prints orange. Cadmium nitrate turns prints red.
Analog
Chemical compound structurally similar to another but differs slightly in composition. Like the original with a light difference in atomically structure.
Ninhydrin Analogues
MN and MTN. Both are amino acid-specific reagents that are structurally like ninhydrin but with improved capabilities. Both luminesce and are visible without a light source. Cheaper to produce but not as accepted.
Physical Developer (PD)
Used when porous substrates have been wetted. Reacts to water-soluble sebaceous components of latent print residue.
PD Signature
Dark grey to black due to the silver metal along the latent print ridges
Benefits of PD
Can develop very old fingerprints. Can be used on wet/wetted items. Improves quality of fingermarks after DFO and ninhydrin.
Disadvantages of PD
Long and time consuming, acidity weakens paper, silver may deposit in marks/creases/indentations/scratches, short shelf life, permanently stains any surface
Oil Red O (ORO)
Lipophilic stain for developing prints on porous surfaces that have been wet. Better development than PD on some types of paper.
ORO Application
3 step process involving coloration, neutralization, and drying
ORO Signature
Red ridges against a pink background
Nile Red (NR)
Lipophilic stain seen with 555 nm barrier filter. Excellent results on heavily sebaceous fingermarks.
Disadvantages of NR
Expensive and dangerous. Nile blue is cheaper and safer.
Small Particle Reagent (SPR)
To treat nonporous surfaces exposed to or immersed in water (even over 30 days). Fine particles of powder mixed with a surfactant. Reacts with fatty residue of latent prints.
Surfactant of SPR Compositions
A weak detergent solution/surface agent. Key ingredient. Keeps fine particles suspended and evenly spreads the powder over a wet surface. Concentration can affect the quality of prints (higher concentration=weaker prints).
Which SPRs are used on which surfaces?
Black charcoal powder or molybdenum disulphide for grey prints on light surfaces. Titanium dioxide or zinc carbonate for white prints on dark surfaces.
Fingermark detection on fabric substrates
Ridge detail only possible with very fine weave patterns. Always test with similar fabrics first.
100% Cotton
Behaves as a porous surface. Amino acid reagents, indanedione, ninhydrin, and gel lifters.
Synthetic fabrics (like polyester and nylon)
Treat like non-porous. CA fuming followed by dye stain.
Adhesive Substrates
Process non-porous (CA), then adhesive side powder suspension, then CA dye stain.
Metallic Substrates
CA fuming with Rhodamine G6.
Fingerprints on Guns and Ammunition
Low success rate. Can only be developed on exterior, magazine, and cartridge/cartridge case. Perspiration is acidic and may cause latent prints to be visibly etched into the cartridge surface without development. CA fuming and then dye staining.
What affects recovery of fingerprints on guns and ammunition?
Heat from firing, ejection friction, falling on ground, fingerprint resistant coating on guns, textured surfaces for grip.
Amido Black
Stains the protein in blood fingerprints a bluish-black colour. Methanol based formula for nonporous. Ethanol formula for porous and non porous but lighter prints but cheaper and safer.
Acid Violet 17
Protein dye stain for porous items. Sprayed or dipped, stained, and then rinsed with water. Similar to amino black.
Disadvantages of Amido Black and Acid Violet 17
Purple and black/blue colours not easily seen on dark background
Acid Yellow 7
Used for bloody fingerprints and footprints on nonporous substrates. Fluoresces yellow-green under blue-green light. More effective on faint impressions but can be used on dark or patterned substrates.
Thick Powder Suspensions
“Sticky-side powder”. Black powder in a detergent solution. Must be brushed on (bc she thiccc), left for a short time, and then rinsed with water.
Benefits of Thick Powder Suspensions
Very effective on adhesive surfaces. Can be reapplied if weak prints are developed. White powder suspension will show prints on both sides of dark coloured tape.
