Criminalistics Exam 1

forensic science

any science used for law, solve civil disputes, protecting and informing public health

CSI effect

damaging to the field and public perception of forensic work

Crime Lab units

fingerprinting

toxicology

ballistics

toolmarks

DNA analysis

Trace

Controlled substance

Entemology

Pathology

anthropology

documents

cyber

Considerations when creating a standard

1. underlying theories inspire techniques and methods (chem, bio, geo etc)

2. Scientific method validate analysis techniques

3. Apply techniques/methods to evidence for criminal investigation

4. intemperate findings

5. May testify in court

Frye standard

-Admissibility of scientific evidence into a courtroom.

-Evidence must be generally accepted by scientific community

Daubert decision

Frye standard not a requirement for admissibility

Trial judge is the “gatekeeper”

Interobserver error

A high error rate means more variation in the lab when your research is compared to other findings

Intraobserver error

A low error rate means you get the same results consistently in the lab when you do your own research

Class Characteristics

associated with a group

Individual Characteristics

Associated to a common source

Physical Evidence

any and all objects that can establish a crime has or has not been committed or can provide a link between a crime and its victim or perpetrator

Physical evidence purpose (Identification)

Determine physical or chemical ID near absolute certainty.

Physical evidence purpose (comparison)

Determine whether a specimen and a control specimen have the same origin

Compound microscope

2D view & 25-1200 times magnification
Magnification = magnifying power of objective lens x magnifying power of the eyepiece lens.

Comparison Microscope

2 independent objective lenses
joined together by an optical
bridge to a common eye piece +
system of mirrors & lens
• Side-by-side view split evenly
• Left on left, right on right
• Great for ballistics
• Vertical/reflected illumination

Stereoscopic Microscope

• Stereo(binocular) or dissecting microscope
• 2 monocular compound microscopes
specifically spaced to create a 3D image
• Lower magnification than compound 10-125
times magnification
• Right-side up and non-reverse image
• “Gross”/preliminary evaluation
• Larger, bulky specimens

Polarizing Microscopy

Becke line: halo “white”
border around material with
higher RI
• Birefringent materials: split light beams in 2, each with a unique refractive index (RI)
• RI helps ID material + oil/liquid with known RI

Morphology of hair

Follicle

root/bulb

shaft

tip end

Morphology of hair shaft

Medulla

cortex

cortex cell

cuticle

cuticle

Exterior scale structure help with species ID

Coronal, Spinal, Imbricate

Cortex

Main part of shaft and houses pigment

Medulla

Cellular column running through center of the hair parallel to the shaft.

continuous

interrupted

fragmented

Medullary index

diameter 1/3-human 1/2-nonhuman

Hair

not possible to individualize human hair to a specific head or body

Root

hair roots may contain DNA, Mitochondrial=maternal line, Nuclear DNA is best.

Natural fiber

wool, cashmere, fur cotton

Manufactured Fiber

Regenerated: rayon, acetate
Synthetic: nylon, polyester, acrylic, spandex

Synthetic fiber

polymers

Fiber analysis

To ID or narrow down possible organ of fiber.

The best case scenario is a fiber with torn edges. need to match morphology, dye, chemicals

Glass

Hard. Silicone oxide(sand)+various metal oxides

Kinds of glass

Soda lime (windows and bottles)

Float (flat windows)

Tempered (cars side windows)

Laminated (cars windshields)

Soda lime

sodium carbonate and calcium carbonate

float

molten tin

tempered

Rapid heating and cooling cycle, dice shatter

Laminated

3 layers - glass plastic glass

Intensive property

the same regardless of sample size

Light

moves in a continuous wave, stream of energy particles

Classification of glass

1. FBI database densities and RI

2. LIBS Laser induced breakdown spectroscopy elemental analysis

Broken glass analysis

Radial factures

concentric fractures

3R rule

Radial cracks form a Right angle on the reverse side of the force