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UTD - BIOL 3318 Spring 2011: Forensic Biology - Instructor: Anwu Zhou, PhD


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Forensic Science

The application of science to the criminal and civil laws that are enforced by police agencies in a criminal justice system.


Services of a crime laboratory.

3 Major Categories of Forensics


Physical Forensics

Branch of science that deals with matter (anything that has mass, takes up space or energy, or involves the ability of a machine or other object to do work)

Crime scene technicians/investigators

collect many different types of evidence at a crime scene

Forensic engineers

reconstruct motor vehicle accidents, analyze mechanical systems (e.g. airbags), structural analysis

Ballistics experts

study firearms evidence

Latent fingerprint examiners

find, develop, and match fingerprints

Forensic imaging

digitally "age" photos of missing persons, suspects

Document examiners

study the authenticity of different types of documents (wills, ransom notes, money)

Chemical Forensics

Deals with chemical substances, drugs, or poisons found at crime scene or in a body, Unlikely to visit the crime scene

Forensic toxicologists

test body fluids/tissues/organs for the presence of alcohols/drugs/poisons (specialized form of chemist)

Arson/explosive specialist

determines origins of fires and mass disasters

Biological Forensics

Pertaining to anything that is, or once was, living, Unlikely to visit the crime scene


test for the presence of biological material, bodily fluid

DNA analysts

uses DNA to identify individuals, compares suspects to evidence

Medical examiners/coroners

(forensic pathologists): perform autopsies and identify cause of death

Trace evidence analyst

hair, fibers, paint

Forensic entomologists

study insects and their role in occupying the body after death

Forensic anthropologist

studies the origin of humans, skeletal reconstructions, lifestyle determination

Forensic odontologists

identify persons based on dental records, bite mark imprints

Computer/internet forensics

follows computer crime trail

Forensic accounting

financial fraud detection, auditing


personality profiling

Oldest forensic laboratory

LAPD in 1923


Formed by J. Edgar Hoover, 1932, Largest Forensic Lab in World

What's the need for Forensics Labs

Supreme Court requested police give greater emphasis to securing scientifically evaluated evidence
Lack of confessions/protecting criminals constitutional rights
Increase in crime rates
Advent of DNA profiling

FBI (Dept of Justice)

Federal Bureau of Investigation - broad investigative powers

DEA (Dept of Justice)

Drug Enforcement Administration - analysis of seized drugs

Bureau of Alcohol, Tobacco, and Firearms (Dept of Justice)

analyze alcohol, documents of tax law, examining weapons, explosives

US Postal Inspection Service

criminal investigations related to postal service

Basic Services of crime lab

Physical science unit (chemistry, physics, geology)
Biological science unit
Firearms unit
Document examination unit
Photography unit

Optional Services of crime lab

Toxicology unit
Latent fingerprint unit
Polygraph unit
Voiceprint analysis unit
CSI unit

The Frye standard (set in 1923)

The Frye v. United States decision set guidelines for determining the admissibility of scientific evidence into the courtroom.
The evidence in question must be "generally accepted" by the scientific community.
Frye Not Absolute

The Daubert Criteria (set in 1993)

Trial judges are ultimately responsible as "gatekeepers"

Expert Testimony

Presenting in a court of law findings and conclusions about a case
Must be qualified by a judge
May give opinion
Job is not to convict

Functions of a Forensic Scientist

Analysis of physical evidence
Expert Testimony
Training in the proper recognition, collection, and preservation of physical evidence

Basic CSI Procedure

Physical evidence recognition
Proper collection & packaging & preservation
Scene reconstruction

Types of Physical Evidence

Tool marks
Almost anything!

Info on the Corpus delicti

Latin meaning "body of evidence"—is the proof that a crime has taken place. When applied to a criminal case, proof of a crime must be shown in order to convict a person of the crime (fact finding)

Info on the Modus Operandi

Latin meaning "Method of operations"— criminals may repeat their behavior and/or techniques providing a signature

Linking persons, scenes, objects

linking suspect and victim is the most crucial information; Locard Exchange Principle at work

Locard Exchange Principle

States that whenever two objects
come into contact, a mutual
exchange of matter will take place
between them


The Integrated Automated Fingerprint Identification System


The Combined DNA Index System


The National Integrated Ballistics Information Network


The International Forensic Automotive Paint Data Query


Shoeprint image capture and retrieval

Primary crime scene

site of first criminal activity

Secondary crime scene

any subsequent crime scenes

Macroscopic crime scene

composed of many crime scenes

Microscopic crime scene

refers to the specific types of physical evidence found at macroscopic crime scenes

preliminary walk-through must be
done to note the following items

1. Mentally prepare a reconstruction theory
2. Any evidence that requires immediate protection or processing
3. Entry and exit points
4. Record initial observations of who, what, when, where, and how
5. Assess scene for need of additional personnel and agencies as required

Crime Scene Documentation

1. Notes taking
2. Videography
3. Photography
4. Sketching

What is biological evidence?

Seminal fluid
Tissue (muscle & organs)
Umbilical cord
Personal items: tooth brushes, hair combs, underware, eyeglasses, cigarette butts...

Most common biological evidence



Study of bodily fluids

Blood Components

Blood is composed of erythrocytes (red blood cells), leucocytes (white blood cells), thrombocytes (platelets), and plasma
We are interested in white blood cells (source of DNA)

White blood Cells

500,000 per drop, life span of 2-3 days


15-150 million per milliliter; heads are the source of DNA (contains a nucleus)

Blood Visual Examination

wet or dry, red to orange, brown to black

Semen Visual Examination

clear or yellow, dry and crusty

Chemiluminescent assays


Colorimetric Assays


Fluorescence assays


Presumptive testing

Providing a reasonable basis for belief or acceptance
Termed 'presumptive' due to possibility of false positives
Answers the question "Is it biological?"


Presumptive for blood, reacts with hemoglobin in RBC
Light is emitted as a product of the chemical reaction
Results in production of blue-white light
Photograph immediately
Works very well on odd stains
Reacts with metals and bleach (cause false positive)
Used mainly at the crime scene


Presumptive for blood, reacting with hemoglobin in presence of hydrogen peroxide
Color change to pink --- Colorimetric Assay
Result must be read immediately (60 seconds)
Reacts with potatoes and horseradish


Presumptive for blood, reacts with hemoglobin
Color change to blue-green after addition of hydrogen peroxide
Reacts with plant extracts, inorganic compounds


Presumptive for blood
Thin white strips with a chemical on tip that reacts with hemoglobin
Positive color change indicated by green or blue
Bleach may cause a false positive
Easy to use at crime scene


Presumptive for blood, reacts with hemoglobin
Must be exposed to a particular wavelength of light 425-485 nm from alternate light sources (ALS)
Emits yellowish-green color

Acid Phosphatase

Presumptive for seminal fluid
Can be detected in all males, vasectomized or not
Seminal fluid contains a higher level of AP than any other body fluid
Cauliflower produces false positive

Detection of Saliva

Not routinely performed
Amylase: enzyme present in saliva to aid in digestion; found in humans, animals, and plants
Detected by application of starch-iodine

Experimental Controls

Proper controls tell us that our experiments are working as expected and that we can trust the results

Positive Control

Tests the reagents/chemicals to ensure that they are working, produces a positive result in presence of a known sample

Negative Control

Tests the reagents/chemicals to ensure erroneous positives do not result
Controls for contamination

Challenges to biological samples

Environmental: temperature, humidity, cleanliness
Contamination: inadvertent addition of an individual's biological material /DNA
Mixtures: victim/suspect


Using the microscope to observe and analyze evidence not clearly seen with the naked eye (trace evidence)


something that comes from an animal source (mammals)


can be of plant origin, like cotton, linen, or made synthetically

Hair 3 anatomical regions


Stereo binocular microscope

Renders objects as 3D
Utilizes reflected light
2 eyepieces
Preliminary characteristics
are examined

Compound binocular microscope

Utilizes transmitted, bright light
Sample becomes transparent as light travels through it
Magnification up to 1200X the object's size
Morphological characteristics are examined

Comparison Microscope

Allows for simultaneous viewing of 2 samples
2 microscopes connected by an optical bridge
Can allow for superimposing images


Outside covering of the hair shaft
Formed by overlapping scales that always point toward the end of the hair
Scales are made of kerain
Provides two important features that make hair a good piece of physical evidence (attributed to the cuticle)
1. Resistance to chemical decomposition
2. Ability to retain structural features over a long period of time


The "meat" of the hair strand
Contains pigment granules
Examined using a 'wet mount'


Appears as a central canal running through the hair
Can be a dominant feature in animals
Not all hairs have a medulla, even within the same individual
Described as continuous, fragmented, or absent
Shape of medulla is important to distinguish between human and animal

Life Cycle of Hair

3 phases
Anagen = active growth
Catagen = transition
Telogen = resting


Growing stage
May last up to six years
85% of hair in anagen phase
Must forcibly pull hair to see anagen root, usually will have follicle around the root
Excellent source of DNA

Catagen Root

Transition phase
1% of hair in catagen phase

Telogen Root

Resting phase, ready to fall out
Loose 50 hairs per day
End is swollen like a cotton swab
14% of hair in telogen phase
No nuclear DNA


Natural hair color depends on the presence , amount, and distribution of melanin, a natural pigment found in the cortex
Melanin is housed inside granules which are scattered throughout the cortex with no set pattern or amount
Provides for hair color variation
Mixtures of these 2 create hair color via the type of melanin and size of granule


a black pigment


red/yellow pigment

Coronal or crown scales

resemble stacks of paper cups; found on rodents, bats

Spinous or petal

triangular; found on cats, seals, minks

Imbricate or flattened

overlap like roof shingles; found on humans and some animals

Caucasoid (European) Hair

fine to medium coarseness
straight or wavy
fine to medium sized granules
Granules evenly distributed

Negroid (African) Hair

Regularly curly or coiled
Larger pigment granules
High density of granules

Mongoloid (Asian) Hair

Coarse, straight
Wider in diameter than other groups
Medulla is continuous and wide
Can have a characteristic reddish color

Head hair

Most alterations (coloring, cuts, environmental insults)
Head hairs obtained years after a crime are generally not suitable for meaningful comparisons
Obtain 50 full length reference hairs from various sections of head

Pubic Hair

Not subject to as much variation
Obtain 25 reference hairs

Facial Hair

Beard and mustache hair are helpful

Limb Hairs (arm or leg)

Generally not meaningful

When conducting a hair comparison, look for the following

Body Area
Color and shape
Tips (broken, split, singed, cut)
Pigment density
Artificial treatment (dying, bleaching)

Nuclear DNA

found in nucleus of cell (only in hair roots)
can only be obtained from anagen hair roots
Must be pulled and have the follicle on them to be useful
Hair shaft can be used for mitochondrial DNA analysis
Especially important since it is most likely to find telogen hairs at crime scene

Mitochondiral DNA

found in mitochondria (hair shaft)
are organelles involved in energy production
They contain their own DNA
Maternally inherited

Coroner System

Originated in England around 1194
Had to be a Knight with a particular income
Appointed or elected
Judicial responsibilities
Investigated sudden deaths
English law is basis for US law
No provision for a coroner in US Constitution
Federal government had no death investigation operations (except DC) until 1990
Each state enacted coroner's law
Elected county official


Began to work in hospitals in 19th century using microscopes to examine tissue
Doctors became known as "pathologists":
Greek "pathos" = suffering or disease
"logos" = word or writing
Pathologists studies disease, its cause, and its diagnosis

Anatomic pathologists

autopsies, tissue examination; later utilized by police and ME

Clinical pathologists

body fluids

Medical Examiner

Educational requirements:
MD or DO degree
4 years post-grad training (residency)
Additional year of training in clinical and/or anatomic pathology in ME's office
Must pass a 2 or 3 day exam to be board certified

Forensic Pathologist's Role

Investigate the deaths of persons who die suddenly and unexpectantly or as a result of injury

Goals of Autopsy

Determine identity if possible
Determine cause of death (what directly led to the death?)
Determine manner of death (how the cause of death came to be)
Determine mechanism of death (biochemical or physiologic abnormality produced by the cause of death that is incompatible with life)

Rigor Mortis

A stiffening of the muscles that occurs following death
Due to the glycogen supply normally found in muscles being exhausted
Observed about 4 hours after death
Disappears during 24-36 hours after death when decomposition of muscle is occurring

Livor mortis

The discoloration of the body due to settling of red blood cells after blood stops circulating
Can be seen within an hour or so after death
Becomes fixed in about 12 hours after death
Disappears with decomposition after 36 hours
Determine the position of body when die

Algor mortis

The cooling of the body that occurs after death, assuming ambient temp is lower than body temp
A body exposed to 18-20°C (64-68°F) drops 1.5°C (2.7°F) per hour for the first 8 hours
Normal body temp is 37°C (98.6°F), thus if a body has been dead for 4 hours, temperature will be 31°C (87.8°F)

Natural Cause of Death

caused solely by disease, without trauma

Accidental Cause of Death

due to trauma occurring from acts lacking a high probability of producing harm or death

Homicidal Cause of Death

death from acts with high probability of producing bodily harm

Suicidal Cause of Death

only difference from homicidal manner is the person who acted

Asphyxial death (due to lack of oxygen to the brain) overlaps causes

Strangulation (mechanical)
Poisioning (chemical)
Electrocution (electrical)

Mechanical Trauma

1. Sharp
2. Blunt
A. Non-firearm
B. Firearm
Low Velocity
High Velocity

Sharp Force Injury

Injuries received from sharp objects: knives, swords, axes
Occurs when applied force exceeds tensile strength of tissue to which the force is applied
Produces incised wounds (not lacerations) with sharp edges
Death occurs by exsanguination: a major artery or heart must be damaged to cause death

Non-firearm Blunt Trauma

Caused by collisions and anything that can be used as a weapon other than a firearm
Usually requires a head injury to produce death
Mechanism of death is often blood that had been aspirated into lungs
Produces lacerations

Firearm Blunt Trauma

Firearm injuries are the most common homicidal and suicidal wounds seen in US - know
Injuries can be classified based on:
1, Propellants (gunpowder or smokeless gp/nitrocellulose)
2. Rifled versus smooth bored weapon (rifles or handguns; shotguns are smooth)
Injuries can be classified based on:
3. High and low velocity (higher the
velocity, extent of injury increases)
- Cut-off point is 300 m/s (328 yards)
4. Penetrating versus perforating
Penetrating wound has entrance wound, but NO exit wound
Perforating, both an entry and exit wound
Distance of barrel from deceased at time weapon was discharged:
Gases and smoke from unburned carbon are projected only a few inches
The gas produces contact or near-contact wounds, produces blackening of the skin and tears the skin

Chemical Trauma

Most common drug is alcohol but rarely kills directly
Legal limit is 0.08% (80mg/100mL)
0.25% (250mg/100mL) can cause coma
0.30% (300mg/100mL) slows breathing enough to cause death
Cocaine overdoses
CO: cuts off oxygen to brain, binds to hemoglobin in blood 300X stronger than oxygen
Blood levels of CO as low as 20% can be fatal (in fires, often reaches 90%)
Cyanide: acts similar to CO, distinctive odor like almonds, 50% of population cannot smell cyanide, can be killed by the gases released from cyanide in intestines

Thermal Trauma

Exposure to excessive heat or cold can produce death
Hypothermia: excessive cold
Hyperthermia: excessive heat
Difficult to diagnose
Thermal burns: localized wounds caused by hyperthermia
Above 150°F will produce burn upon contact for a few minutes
Wide range of circumstances cause burns: hot liquids, explosions, fire
Persons who die at scene of fire, usually die from inhalation of CO rather than the fire
Levels of CO in blood can be used to determine death: a 1-2% CO level is evidence person was dead before fire
Gasoline fires kills before person has a chance to inhale excess CO


excessive cold


excessive heat

Electrical Trauma

Low voltage (less than 1000 volts) interferes with beating heart, can produce burns
High voltage causes heart to continually sustain contraction (tetany) that when broken, will allow heart to have normal rhythm, produces burns less than a second

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