Fingerprints

Question 1

Definition of criminalistics

Answer 1

Definition o Forensic Science
- Application of various scientific and technological methods to the investigation and resolution of legal matters
Criminalistics
- the largest subdivision of forensic science
- Involves the collection, preservation, and analysis of physical evidence generated by criminal activityby applying the laws of physical sciences and natural sciences

Based on Locard’s exchange principle

A person committing a crime will bring something into the crime scene and leave with something from it

Question 2

Differences between Direct evidence and Circumstantial evidence

Answer 2

Evidence
1) Direct: firsthand observations eyewitness account, video camera, confessions.

2) Circumstantial:indirect evidence ;implies a fact, but not directly prove it; more reliable than testimonial evidence
- Physical – bullets, weapons, shoeprint impressions, fibers
- Reduce the number of suspects to a specific, smaller group of individuals

• Biological – body fluids (blood, saliva, sweat, tears), hair, bone, tissues, urine, feces, animal material, insects, bacteria, fungi
• Make the group of suspects very small, or reduce it to a likely individual

Question 3

Examples of Trace evidence

Answer 3

Small but measurable amounts of physical or biological material found at a crime scene
Examples:
Hair
- Fire and explosive residues
- Plastics
Fibers
- Fingerprints
- Glass fragments
Soil
- Paint chips
-Chemical residues

Question 4

List and describe the THREE types of fingerprints that may be found at a crime scene.(6 marks)

Answer 4

1. Plastic prints are raised friction ridges physically pushed into the substrate, creating a mold of the friction skin ridge structure. Substate are soft material such as soap, soft wax, wet paint, clay, heavy grease. They are three-dimensional.
2. Visible prints are made when a finger or thumb touches a surface after in contact with a colored material such as blood, ink, dirt, paint, grease, chalk, mud. These prints are visible.
3. Latent or invisible prints are impressions caused by the transfer of body perspiration or oils present on finger ridges to the surface of an object. They are not readily visible, thus requires optical enhancements, physical methods or chemical reagents to be developed.

Question 5

What is the THREE principles of fingerprint causing it to have a role in the criminal justice system?

Answer 5

1st principle: Uniqueness

No two people have the same fingerprints, including identical twins
An individual characteristic

2nd principle: Persistence (permanence)
- A person’s fingerprints remain unchanged throughout their lifetime
- Friction ridges (hills) and furrows (valleys) appear on palms, soles, and the ends of the fingers and toes

3rd principle: General ridge patterns
- Can systematically classify into 3 patterns
- Loops, whorls and arches
8 subcategories

Question 6

Discuss the role of fingerprints in the criminal justice system.

Answer 6

Compare unknown prints collected from a crime scene to the known prints of victims, witnesses and potential suspects
Connect the crime to a person who may have been present at the scene
Murder: suspected weapon Bank robbery: a robbery note Burglary: broken window
May link suspects to other unsolved crimes

Question 7

Discuss how fingerprints on the following surfaces should best be visualized, documented, and preserved.
a) Visible fingerprint on the white wall of a house
b) Latent fingerprint on the white wall of a house
c) Latent fingerprint on a piece of paper
d) Latent fingerprint on a pair of scissors
e) Latent fingerprint on a phone which has been dropped into the
water (i.e., wet)

Answer 7

a) The visible fingerprint should be photographed. The wall cannot be
removed and transported, so the photograph will be the document
and record of the fingerprint. To preserve it, tape lifting, or silicone (mikrosil) casting should be performed depending on the surface
which is flat or textured/irregular.

b) Develop the latent fingerprint with dark-colored fingerprint powder (i.e., dusting). The visible fingerprint are then be photographed. The wall cannot be removed and transported, so the photograph will be
the document and record of the fingerprint. To preserve it, tape
lifting, or silicone (mikrosil) casting should be performed depending
on the surface which is flat or textured/irregular.

c) The piece of paper should be collected from the scene, packaged, and transported to the crime laboratory. At the laboratory, the
latent fingerprint should be visualized with ninhydrin. The fingerprint should be photographed after the latent fingerprint
turns to purple color. The paper with the visualized fingerprint should then be secured for storage.

d) The pair of scissors should be collected from the scene, packaged,
and transported to the crime laboratory. At the laboratory, the pair
of scissors should undergo superglue fuming. The fingerprint should
be photographed after the latent fingerprint turns to white color.
Fluorescent fingerprint powder is applied afterwards. To preserve it, silicone (mikrosil) casting should be performed

e) The phone should be collected from the scene, packaged, and transported to the crime laboratory. At the laboratory, the phone
should be sprayed with small particle reagent (SPR). The fingerprint should be photographed after the latent fingerprint is developed.
To preserve it, tape lifting, or silicone (mikrosil) casting should be performed depending on the surface which is flat or textured/irregular

Question 8

What are the TWO components of latent fingerprints?
* Intrinsic components. Examples?
* Extrinsic components. Examples?

Answer 8

Intrinsic components: natural secretions of
the glands, in addition to metabolites and
traces of drugs.
- Water (98-99%), amino acids, proteins,
urea, uric acid, lactic acid, carbohydrates

Extrinsic components: substances that a
person may have contact with during the
day
- Examples: dust, cosmetics, blood, grease food

Question 9

List the techniques for developing and preserving latent fingerprints on porous
and nonporous objects.
Developing latent fingerprints:
* Physical method: Fingerprint powder (dusting); Small particles reagent
(SPR)
* Chemical method: Ninhydrin; Super glue fuming (Cyanoacrylate fuming)

Answer 9

Porous - Absorbent
Non-porous surface- Do not absorb

Physical method - based on the adherence or
solubility of their compounds to the
components present in latent prints
1) Fingerprint powder (dusting) (color contrasting with the background)
2) Small particles reagent (SPR)

Chemical method - some chemical reaction
occurs between the residue of the fingerprint
and the reagent
3) Ninhydrin
4) Superglue (cyanoacrylate) fuming

1. Color selection: use a colored powder to
   provide a visual contrast to the surface
   being processed
   Principle: Mechanical attraction between finely
   divided particles and the moisture and oily
   components in a latent print
   (Adhesion)

1) Regular (e.g., the Black Powder and the
White Powder)
2) Metallic (e.g., Aluminum Powder and
Magnetic Black Powder)
3) Fluorescent (e.g., the GREENescent and the
PINKescent Fluorescent Fingerprint Powder)

2) Metallic (e.g., Aluminum Powder and
Magnetic Black Powder)
Have metal in their composition, such as iron,
aluminum, copper, bronze…
Magnetic → application is done with a
magnetic dusting brush that picks up a
“fuzzy ball” of magnetic powder that is then
“brushed” over the print
Advantage: no brushing,→ much lower chances of fingerprint destruction
Principle: Magnetic powder selectively adheres to the latent prints due to its affinity for oils and moisture

1. Tape lifting
   -Place clear adhesive tape
   -Only for perfectly flat, smooth surfaces
   Attach the tape at the base of the print, gently press the tape down and press upward and beyond the print = eliminate air bubbles
   Preserving developed prints
   - Lift the tape from the object and place on
   a contrasting background card (i.e., with
   a contrasting color to the powder used)
2. Silicone casting (Mikrosil)
3. Gel lifter

2) Small particles reagent
A physical development technique in which
small black particles adhere to the fatty
substances left in print residue and is useful
on many different nonporous surfaces.
Wet surfaces and under water
Choose fingerprint developers which
interact with water-insoluble compounds
Choose fingerprint developers which must
not applied dry (i.e., powders)
Use SPR; since it adheres onto oily
fingerprint compounds (sebum)

1) Choose the black or white SPR prefilled
capsule based on background color of the
item being processed
2) Spray Method - spray SPR
solution onto surface
area and rinse with tap
water.
3) Allow completely to dry
4) Photograph and lift/cast

3) Ninhydrin
Porous surfaces, especially on paper.
Ninhydrin: pale-yellow substance
Reacts in contact with amino acids,
generating a non-fluorescent purple
product known as Ruhemann’s Purple
i. Dipping method: completely submerge the
item in the working solution for 5-10 secs
ii. Spray method: spray the item to
completely saturate the item
iii. Brush method: dip the brush into solution
and brush directly onto the item

i. Dipping method:
completely submerge the item in the working solution for 5-10 secs
ii. Spray method: spray the item to
completely saturate the item

A second treatment with metal salts (e.g.,zinc or cadmium)
Change the color of the developed fingerprint with luminescence properties