Forensic Science Unit 2

Forensic science

Application of science to both criminal and civil laws that are enforced by police agencies

Locard’s principle

when 2 objects come into contact with one another, there is an exchange of materials between them

Physical science unit

Examine physical evidence/trace evidence

Biology unit

DNA, profiling hair, fiber analysis, bodily fluids, plant/wood analysis

Firearms unit

Bullets, firearms, trajectory, direction, source, residue

Documentation unit

Handwriting, typewriting, ink, paper, erasures

Photography unit

Record and analyze evidence via special photographic techniques

Toxicology unit

Exam fluids and organs for presence of drugs or poisons

Latent fingerprint unit

Process/examine latent fingerprint evidence

Polygraph unit

Administer lie detector test and analyze results

Voiceprint analysis unit

Analyze telephone threats and recorded messages

Crime-scene investigation unit

Collects and preserves physical evidence

Psychiatry

Examine behavior, determine competency

Odontology

Dental records, bite marks

Engineering

Failure analysis, accident reconstruction, causes/origins of fires/explosions

Computer and digital analysis

Identification, collection, preservation, analysis of data from computers and digital devices

Entomology

Study of insects to determine time of death/location

Pathology

Determination of cause of death, autopsy

Anthropology

Analysis of bones

CSI Effect

Television shows provide individual with unrealistic expectations regarding the collection, processing and analysis of evidence and crime solving due to misinformation, quick results, all-knowing team members, etc.

First arriving officer

Who secures the crime scene?

Individual characteristics

Properties of evidence that can be attributed to a common source with an extremely high degree of certainty (fingerprints)

Class characteristics

Properties of evidence that can be associated only with a group and never with a single source (car paint for a specific make)

IAFIS

National fingerprint database

CODIS

DNA profiles

NIBIN

Firearms and bullet markings

PDQ

Automotive paint

SICAR

Shoe prints

NamUS

Missing persons

Identification

the process of determining a substances’s physical or chemical identity

Comparison

the process of ascertaining whether two or more objects have a common origin by testing a suspect specimen and a standard/reference sample

Manner of death

Determination made by a forensic pathologist of the cause of death and there five broad categories

Homicide

A nonaccidental death resulting from grossly negligent, reckless or intentional actions of a person

Suicide

A death caused by an individual taking his/her own life; lethal intentions

Accidental

A death that resulted without intent to cause harm through gross negligence on the part of the perpetrator or victims 

Natural

Deaths resulting from disease or continual environmental abuse (drug abuse, exposure to chemicals over long periods of time)

Undetermined

Is only used in cases where a rational classification cannot be made based on the physical finds of an autopsy or the absence of anything meaningful in toxicological and microscopic examinations

Periodic table

Table/chart with all the known elements

Melting

Solid to liquid

Sublimation

Solid to gas

Freezing

Liquid to solid

Desposition

Gas to solid

Condensation

Gas to liquid

Vaporization

Liquid to gas

Solid - Most dense, particles close and vibrate

Liquids - Indefinite shape, definite volume, flows

Gases - Indefinite shape and volume, chaotic, random, rapid

What are the main properties of solids, liquids, and gases?

d = m/v

Substances that are less dense will float

Substances that are more dense will sink

What is density? What will float and what will sink?

Dispersion

Separation of light into colors

Refraction

The bending of light

Glass is hard, brittle, amorphous, solid made of sand mixed with metal oxides

The main component of glass is sand

What is glass and what is the main component of glass?

Soda-lime is used for windows and glass bottles

Borosilicates are used for headlights and Pyrex

Tempered is used for side and rear automobile windows

Laminated is used for windshields

What are the types of glass and examples for each?

Flotation

Method of changing the amounts of a liquid until the solid glass is suspended (density of liquid = density of the glass)

The hole is wider on the exit side

How can the bullet hole in glass be used to determine the direction of the bullet penetrated/exited?

Look at where each fracture ends or terminates

Ex: 1st none of the fractures will terminate at another fracture, 2nd will have fractures that end at the 1st

How can one determine the sequence of bullet holes made in glass?

Hair

Appendage of skin

Cuticle

Scale-like outermost layer of hair

Cortex

2nd layer with pigment of hair

Medulla

Cells like central canal of hair

Cuticle

What layer of hair is most often used to determine the species it came from?

Cortex

What layer of hair contains the pigments that give hair its color?

Anagen - 1st stage of growth up to 6 years

Catagen - 2nd stage, slower growth (2-3 weeks)

Telogen - 3rd stage, hair is pushed out / naturally shed

What are the 3 stages of hair growth

DNA

How can hair be used to determine the gender from which it came from?

Cotton

What is the most common plant fiber used to make clothing

Bagged separately

If loose, removed with forceps and placed in a small sheet of paper

How should fiber evidence be collected and stored?

Visible light microspectrophotometer

Small sample sizes and nondestructive

What instrument should be used to compare the color of fiber evidence and why?

Color and diameter

What properties are used to compare synthetic fibers?

Natural polymer

It is found in wood

What is cellulose and where is it frequently found in nature?

Protons (positive charged particle found in the nucleus)

Neutrons (neutral particles found in the nucleus)

Electrons (negative particles found outside of the nucleus)

What are the 3 subatomic particles of an atom and where are each located in the atom?

Isotope

An atom with the same number of protons (atomic number) but different number of neutrons (masses)

Neutron activation

A highly sensitive and nondestructive analysis method for identifying trace elements. Uses a nuclear reactor to provide a source of neutrons to bombard atoms producing radioactive isotopes. To identify the radioactive isotopes one must analyze/measure the energy of the gamma rays released

Hit-and-runs

What types of crimes often leave paint evidence?

Make, model, and year

What can be determined about a vehicle using the PDQ database?

Pyrolysis

Solid materials including paint are heated so they will decompose into numerous gaseous products to flow through the GC column that produces a pyrogram that can be used to identify and compare the binder makeup of paint samples

Gross appearance using low magnification

Regarding soil evidence, what is first looked for/at?

Any object with suspected soil samples should be collected and packaged separately in leak-proof containers

Reference samples should be collected from various points within a 100-foot radius of the scene and then packaged in a druggist fold or a solid container

How is soil evidence collected and preserved?