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Forensic Science: Final Exam Review
Unit 1: Crime Scene Investigation
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Forensic Science: The study and application of science to matters of the law
Physical Evidence: An object or substance that is used to prove elements of a crime
Testimonial Evidence: A verbal account of events or details of a crime given by a witness and/or
expert
 Circumstantial Evidence: Evidence that is collected (either physical or testimonial) that is used
INDIRECTLY to prove elements of a crime. This type of evidence DOES NOT PROVE GUILT!
 Expert Witness: A person who is specially trained and certified in an area that allows him or her to
testify in court (i.e. Medical Examiner, Blood Spatter Expert)
 The Frye Standard: Expert opinion based on a scientific technique is admissible only where the
technique is generally accepted as reliable in the relevant scientific community (The “General
Acceptance Rule”)
 The Daubert Standard: Scientific technique admissible in court if it is:
o Testable
o Peer-Reviewed
o Rate of Error must be given (exception to rule #3: fingerprints)
 Miranda Rights: Rights that are guaranteed by the Constitution of the United States of America. An
individual MUST be read his or her rights prior to being arrested.
o Right to remain silent
o Anything you say can and will be used against you
o Right to an attorney
o If you cannot afford an attorney, one will be appointed to you
o If you answer questions without an attorney, you have the right to stop
 Probable Cause: The standard by which an officer has the grounds to obtain a warrant to search
and/or arrest an individual
 Individual Characteristics: Features or details that link a piece of evidence to one single source
(i.e. DNA, Fingerprints, Serial Numbers)
 Class Characteristics: Features or details that link a piece of evidence to a group of sources (i.e.
Tire Tracks, Shoe Prints)
 Crime Scene Reconstruction: To recreate the crime scene in order to determine the chain of events
that led up to a crime
 Motive: The reason a crime was committed
 Means: The weapon, tool, or strength used to commit the crime
 Opportunity: The window of time during which the crime was committed
 Chain-of-Custody: A written record of all people who have had possession of an item of evidence
(to ensure its validity and avoid contamination)
 Control Sample: A known evidentiary sample that is collected in order to compare unknown
evidence samples collected from the crime scene, victim, and/or suspect. (i.e. A suspect’s
fingerprints are collected as a control sample to compare it to the fingerprints found on a knife
near the victim)
Crime scene protocols:
 First Responder Responsibilities:
o Secure/Isolate the scene
o Safety of victims
o Witnesses/statements
o Safety precautions
 Crime Scene Investigator Responsibilities:
o Documentation: pictures, sketches, notes
o Search Method
o Collection/Packaging of evidence
o Deliver evidence to the lab (chain-of-custody)
Order of protocol:
 Secure and isolate the crime scene
 Help anyone who is injured
 Process the crime scene
 Documentation
o Photographs
 As many as possible!!
 Overall views, Medium views, Close-up views
o Sketches
 Floor plan (“Bird’s Eye View)
 Triangulation Measurements (for Reconstruction purposes)
o Notes
 Observations using ALL of your senses (except taste!!)
 Conduct a systematic Search
o Spiral
 Outdoors, wooded area
o Quadrant/Zone
 Car/Vehicle
o Line/Strip
 Open Field
o Grid
 Indoor room/warehouse
 Collect, package, and label evidence properly!
o Biological evidence
 Must be dried COMPLETELY and then packaged in a breathable bag or envelope.
o Trace evidence
 Tape-lifted, then packaged in breathable bag or envelope
o Arson and explosive evidence
 Contained in an air-tight canister (metal/plastic) IMMEDIATELY!
 Don’t forget to collect CONTROL SAMPLES!!
o sexual assault cases
 victim(s), suspect(s), sexual partner(s)
o homicides
 victim(s), suspect(s), others who have been in contact with CS
o hit-and-run accidents
 glass, paint, plastic, tire prints from suspect’s car
o braking-and-entering
 window glass, paint, tool marks from items within suspect’s possession
 Legal Considerations: Must have a warrant to arrest and/or search UNLESS:
 Emergency Circumstances
 Injury? Danger? Life-threatening circumstances?
 Prevent loss or destruction of evidence
 “flushing drugs down toilet?”—VERY difficult to prove!!
 Search of person or property in connected to a lawful arrest
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DUI—once someone is placed under arrest they, their vehicle, and anyone in the vehicle may
be searched
 Search made with consent of person(s) involved
 Investigators are invited into someone’s home, office, etc…
Criminal Databases
 NCIC: National Crime Information Center
o General Crimes (burglary, larceny, etc…)
 VICAP: Violent Criminal Apprehension Program
o Sexual assault and homicides (serial crimes)
 AFIS: Automated Fingerprint Identification System
o Fingerprints
 CODIS: Combined DNA Identification System
o DNA
 GRCF: General Rifling Characteristics File
o Firearms
 IBIS: Integrated Ballistics Identification System
o Bulletproof: bullet analysis
o Brass Catcher: cartridge casing analysis
Unit 2: Physical Evidence
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Individual Evidence:
o Evidence that can be linked to ONE (1) individual source (i.e. person, animal, thing,…)
Class Evidence:
o Evidence that can be linked to a group of sources (i.e. persons, animals, things,…)
Biological Evidence:
o Physical evidence that IS/WAS/WAS FROM a living thing
Trace Evidence:
o Extremely small or “invisible” physical evidence
General Physical Evidence:
o A tangible item or substance that is used to prove any element/part of a crime
Deductions from observations include…
o Color, approximate size, texture, smell, shape, ….
Examinations/Forensic Analyses include…
o Mass, volume, density, thickness, temperature, microscopic, refractive index,
chromatography, chemical analysis, ….
Examples of Equipment….
o Balance, graduated cylinder, microscope, thermometer, laser, super glue fuming chamber,
gas chromatograph/mass spectrometer, ….
Unit 3: Trace Evidence
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Locard’s Principle: “Every contact leaves a trace”
Transfer of Trace Evidence
o Primary: Direct Transfer (from Source to suspect/victim/crime scene)
o Secondary: Indirect Transfer (from source to intermediate carrier to S/V/CS)
Soil:
o Applications:
 On Shoes
 Tires
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 At the crime scene
 On victim and/or suspect
o Analysis:
 Color
 Texture
 Grain size
 Density
Hair: Appendage of the skin that grows out of the hair follicle (an organ)
o Parts of Hair:
 Bulb
 Root
 Cuticle
 Cortex
 Medulla
Fibers: The smallest unit of a textile material that has a length many times greater than its
diameter
o Types:
 Natural: Animal or Plant source
 Synthetic: “Man-Made”
o Analysis:
 Fiber Structure
 Comparison Microscope
 Scanning Electron Microscope (SEM)
 Cross-section of fiber (triangular, star-shaped)
 Fiber Colors
 Microspectrophotometer
 spectral patterns and Becke lines
 crystallinity?
 Thin Layer Chromatography: separate components (colors) in dyes
Fingerprints
 The Scientific Method
o Identify a Question
o Gather Information and Resources (Research the Problem)
o Form a Hypothesis/Suggest a Solution
o Test the Hypothesis/Solution
o Analyze Data
o Interpret Data/Draw Conclusions
 --Accept or Reject Hypothesis/Solution
o Re-test!!
o Report Results/Publish Results
 Why the Scientific Method?
o -To decrease bias
o -To provide a systematic, consistent procedure (PROTOCOL)
o -To validate results (3 or more trials resulting in the same/similar data)
 Fingerprints
o Who: All primates (including humans) have friction ridge patterns (fingerprints, palmprints,
footprints)
o What: Raised ridges and furrows that are designed to help grasp items
 At the top of the ridges are sweat pores that release:
 99% H2O
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 1% oils, fatty acids, esters, salts, urea, amino acids
Total volume of 1 adult fingerprint = a few microliters (µL)
o Where: On every surface that a person touches
 Three types:
 Latent (“invisible”)
 Patent/Visible
 Plastic (mold/cast of fingerprint)
o Why:
 Two Rules that allow us to use fingerprints for identification:
 Unique to every individual *including identical twins
 Permanent for an individual’s lifetime
o *friction ridge patterns are formed in the 12th-16th week of fetal
development
o *exceptions: scars and growth (size)
o When: More likely to leave a lasting print when fingers are warm and perspiring (oily)
Categorizing and Analyzing Fingerprints
 HENRY CLASSIFICATION!!!
 ACE-V
o Analysis: Qualitative and Quantitative Assessment
o Comparison: Agreement or Discrepancies between 2 fingerprints
o Evaluation: Consistent? Inconsistent? Inconclusive?
o Verification: A second independent analysis, comparison, and evaluation by another
qualified examiner.
 Categorization
o Level 1: General ridge-flow
 *Pattern
 Arch
 Loop
 Whorl
o Level 2: Formations and combinations
 *Minutiae Points
o Level 3: Details within the formations
 *dimensional attributes of a ridge
Unit 4: Biological Evidence
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Sources of Biological Material:
o Blood
o Semen**
o Saliva
o Urine
o Hair, Teeth, Bone, Tissue
Types of Crimes Involving Body Fluids
o Sexual Assaults**
o Assaults
o Homicides**
o Burglaries
o Desecrations
Process of Forensic Examination of Evidence
o Recognition
 “What is important?” SCREENING/PRESUMPTIVE TESTS
o Identification
 “What is it?” (class category) CONFIRMATORY TESTS
o Individualization
 “Who or What did it come from?” (uniqueness)
Serology: The study of bodily fluids using specific antigen and serum antibody reactions
Secretors: 80% of population have blood antigens (A & B) in other bodily fluids
Types of Bodily Fluids: Urine, Saliva, Semen, Blood
Urine: Waste secreted by the Kidneys
o Water, salts, inorganic ions, and organic compounds (urea & creatinine)
o Tests:
 Azostix: detects Urease
 *false (+) for sweat, semen, vaginal secretion
 Jaffe Test: detects Creatinine *also in sweat, bile, gastrointestinal fluids
o AT LEAST 5-20 mL necessary for possible DNA testing
Saliva: 99.5% water, and 0.5% mixture of mucous, inorganic ions, proteins, epithelial cells
o Tests:
 Phadebas Test, Procion Red Amylopectin Test
 Both tests detect α-Amylase (digestive enzyme) activity (β-Amylase is found in
plants and bacteria)
 Also found in: semen, vaginal secretion, serum, feces, perspiration, breast milk
Semen: Seminal Fluid/Plasma + Spermatozoa
o Screening Tests:
 UV/Alternate Light Source Visualization
 Fluorescence properties of 4-methyl umbelliferyl phosphate (MUP) with
APase
 Seminal Acid Phosphatase (APase) Test:
 Fast Blue B dye +α-naphthyl-phosphate
 APase is a Very stable enzyme (tested after 20 years in dried stains)
 Positive result:: insoluble pink/purple colored product
o Confirmatory Tests:
 “Christmas Tree” Staining (using microscope)
 Spermatozoa is stained red (head), green (middle), and yellow (tail)
 Abacus One Step ABA card p30 Test
Prostate Specific Antigen (PSA or P30) = human seminal fluid protein that is
secreted by prostate gland
 Positive result: dye-colored insoluble band on card
o Individualization: DNA Tests
o Sexual Assault Crimes: Statistics and Information
 78 rapes/hr in USA and 9/10 victims are female
 80% victims are under 30 years old (high risk: 12-34 years old)
 76% of female victims knew their assailant
o What to collect?
 -Clothing
 -Bedding
 -Fingernail/toenail scrapings,
 -Combings (head and pubic hair)
 -Blood: within 12-24 hours after assault
 -Urine: within 36-72 hours after assault
 -Semen: within 24-48 hours after assault
 **4 swabs from each orifice
 DON’T FORGET CONTROLS!!
 Blood:
o A complex mixture of cells, enzymes, proteins, and inorganic substances
o Components:
 -Plasma = 55% of blood
 90% water + 10% metabolites, waste, salts, ions, and proteins
 -Solid portion:
 Erythrocytes = Red Blood Cells (RBC) (no DNA)
o Contain Hemoglobin which transports O2 from lungs to cells and CO2
from cells to lungs
 Leukocytes = White Blood Cells (WBC)
o Primary cells of the immune system—they produce antibodies
 Thrombocytes = Platelets (no nuclei)
o Start the clotting process by initiating the production of fibrin
o If clotted material is removed, left with yellow liquid = serum
o Blood Type:
Antigens are found on RBCs and Antibodies are produced by WBCs
Blood Type
Antigens on RBC
Antibodies in Serum Donor For
Recipient For
A
A
B
A, AB
A, O
B
B
A
B, AB
B, O
AB
A and B
None
AB
All
O
None
A and B
All
O
Rh +
D
---Rh ---D
Universal Donor: OUniversal Acceptor: AB+
*Blood has 100 sub types to further identify victim or perpetrator
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Screening Tests: IS IT BLOOD??
o **All use an oxidizable colorless chemical + an oxidizing agent that is catalyzed by “heme”
(hemoglobin) to produce a visible product (color or light)
 Luminol = product fluoresces when in presence of heme
 Kastle-Meyer test = phenolphthalein (PHTH) that turns bright pink
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DNA
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 Hemastix (Benzidine test)
 Ortho-tolidine test
 Leucomalachte green test
Confirmatory Tests: IS IT HUMAN BLOOD??
o Teichmann Crystal Test
 forms brown visible crystals under the microscope
o Takayama Crystal Test
 forms pink needle-shaped crystals under the microscope
o Precipitin Test
 animal blood that has developed antibodies against human antigens when exposed
to human blood will form a coagulated band at intersection
o Hematrace
 immunological test—utilizes the antibody-antigen reaction
 dye changes color when antibody-antigen coagulation occurs
Individualization: DNA Tests
Physical properties of Blood:
o -A viscous liquid that has the potential to dry!!
o -Consider all of the following when recreating a crime scene based on blood spatter:
 surface texture
 direction the blood traveled
 degree of circular distortion (angle of impact): sin-1(width/length)
 stain convergence lines
 (point of origin = where all droplets originated from)
Uses for DNA/Human Identity Testing:
o Forensic Criminal Cases
o CODIS = Combined DNA Index System
o What type of forensic case is DNA mostly used for?
 Rape/Sexual Assault (more than 2 out of 3 cases)
 Paternity Testing
 Historical Investigations
 Missing Persons Investigations
 Mass Disasters
 Military DNA (“dog tag”)
o What part of a DNA is used for forensic purposes?
 NON-CODING DNA = Spacer DNA = “junk DNA”
 ≈ 0.1% (3 million bases) is unique to an individual person
 ≈ 99.9% same genome fore every person
DNA = Deoxyribonucleic Acid
o “The Blueprint for Life”
Structure of DNA:
o CELL → NUCLEUS → CHROMOSOME → GENE → BASE PAIR
o Double Helix structure composed of base pairs
o Base Pairs: Adenine-Thymine, Cytosine-Guanine
o Genes are what “code” for bodily structures and functions
o Mutations are changes within the genes from one generation to the next
Steps for DNA Processing:
o 1. DNA Extraction
o 2. DNA Quantification
o 3. PCR Amplification
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o 4. Analysis
Two Methods of Processing DNA:
o 1. Restriction Fragment Length Polymorphism (RFLP)
o 2. Polymerase Chain Reaction (PCR) + Short Tandem Repeat (STR)
Restriction Fragment Length Polymorphism (RFLP):
o Larger sample size necessary (dime-quarter sized drop/stain)
o Uses gel electrophoresis
o Restriction enzymes (“chemical scissors”) cut the DNA at specific recognition sites.
 This “cutting” process generates different sized pieces of DNA.
o The DNA fragments are placed in an electrophoresis gel and a charge is applied (+ at one
end and at the other end).
o The different sized fragments migrate towards the + end of the gel.
o The smaller pieces move the fastest and farthest.
o The different sized fragments produce bands along the gel.
o To visualize the bands, x-ray film is used.
PCR + Short tandem repeats (STR)
o PCR: makes many copies of a segment of DNA (DNA amplification)
o Short Tandem Repeats (STR)
 How it works: Restriction enzymes recognize a specific repeating pattern and cuts
the DNA fragment at the beginning and end. This generates different
sized fragments. Gel electrophoresis or capillary electrophoresis is then run to
separate the different fragments.
Mitochondrial DNA (mtDNA) Analysis:
o mtDNA comes from Mother
o If we cannot obtain nuclear DNA (nDNA) it can be used for
o identification purposes
Unit 5: Forensic Toxicology
Toxicology:
 Endogenous Substance: Naturally Occurring in the Body.
 Exogenous Substance: Foreign substance (drug or toxin) in the body
 Toxin: Any material exerting a life-threatening effect upon a living organism.
 A toxic response requires:
o Exposure
o Dose
o Mechanism (how it interferes with bodily functions)
 Toxicology: The science of adverse effects of chemicals on living organisms.
 Toxic effect depends on Depend on:
o Age
o Weight
o Health
o Dose
 Toxic effect can be:
o Hemolytic: Attacking the circulatory system and muscle tissue
o Neurotoxic: Attacking the central nervous system (CNS) causes heart failure and breathing
difficulties
 Receptor: A large molecule on the cell’s surface where neurotransmitters induce their normal
effects.
 Agonist: The drug or poison mimics the action of the transmitter.
 Antagonist: The drug or poison binds to a receptor and blocks the transmitter.
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Routes of entry:
o Orally
 Tablets, capsules, liquids
o Rectally
 Suppositories
o Intravenously
 Injected in liquid form through a needle
o Inhaled through lungs
 Gases, vapors, or particles
o Absorption through skin
 Patches on skin
o Absorption through mucous membranes
 Snorting, sniffing, or under the tongue
 In the body:
o Absorption: The drug/toxin enters the body
o Distribution: The drug/toxin moves throughout the body
o Metabolism: The breakdown or digestion of the drug/toxin into smaller molecules or
products
o Elimination: The removal or excretion of the metabolites
 ED50: The dose size that produces the desired effects of a drug/toxin in 50% of a population/test
group
 LD50: The dose size that produces a lethal effect of a drug/toxin in 50% of a population/test group
 Therapeutic Index = LD50/ED50
o toxic dose/therapeutic dose
Poisons:
 Venom is composed of many different Proteins
 Tissue damage (necrosis) caused by:
o Metalloproteinases
 Muscle damage (necrosis) caused by:
o Myotoxin-a (MA)
 Coagulopathy (Defibrination: loss of fibrin):
o Fibrin-like enzyme
 Platelet Deficiency caused by:
o Phospholipases
 Cardiotoxins: Myocardial depressant protein
 Neurotoxins: Causes weakness and paralysis
 Hemolysin: Loss of hemoglobin from RBCs
o Lecithinase A
 Hemolytic: Targets Circulatory/Muscle Systems
 Neurotoxic: Targets CNS/Heart
 12 Heavy Metals have the potential to be toxic at high levels
 High molecular weight
 Interfere with enzyme systems and the metabolism of the body
Drugs:
 Depressants
o Alcohol, barbiturates, tranquilizers, inhalants, GHB, rohypnol
 Hallucinogens
o THC, LSD, PCP, Mescaline, Psilocybin, Ketamine
 Stimulants
o Cocaine, Amphetamines, Meth, Caffeine
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Narcotics (Opiates, Opioids)
o Morphine, Codeine, Heroin, Darvon, Methadone
Steroids
o Corticosteroids, Anabolic Steroids
Antidepressants
o Tricyclics, MAOI’s, SSRI’s
Unit 6: Ballistics
Unit 7: Serial Killers