Forensic Science Notes

Chapter 7: General Classifications

A. Key Terms

1. Three Classifications of Substances

  • Organic Substances: Contain carbon-hydrogen (CH) bonds (e.g., sugar).
  • Inorganic Substances: Lack CH bonds (e.g., metals, salts).
  • Bonding Formats:
    • Solid: Fixed shape and volume.
    • Liquid: Fixed volume, shape adapts to the container.
    • Gas: No fixed shape or volume, expands freely.
  • Key Difference: Organic substances are carbon-based, while inorganic substances are not.

2. Inner Structure of Substances

  • Protons (P): Positively charged particles in the nucleus.
  • Neutrons (N): Neutral particles in the nucleus.
  • Electrons (E): Negatively charged particles orbiting the nucleus.
  • Key Difference: Protons and neutrons define atomic mass, while electrons determine chemical behavior.

3. Modified Griess Test

  • Purpose: Detects nitrites from gunshot residue (GPR).
  • Process:
    • Uses sulfanilic acid + alpha-naphthol + methanol.
    • Forms nitrous acid, producing a pink color reaction.
  • Key Difference: It’s a chemical test for gunpowder residue, not primer residue.

4. Four Types of Gunpowder

  • Flakes: Used in shotguns and low-pressure handguns.
  • Discs: Smokeless powder (can be amber, yellow, green, or black).
  • Balls: Spherical grains for progressive burning.
  • Cylinders: High-pressure gunpowder.
  • Key Difference: Shape affects burn rate and ballistic performance.

5. SEM Examination (Scanning Electron Microscopy)

  • Purpose: Detects gunshot residue (GSR) at a microscopic level.
  • Process:
    • Uses electron beams to analyze particles.
    • Identifies lead (Pb), antimony (Sb), and barium (Ba).
  • Key Difference: SEM provides high-resolution imaging for forensic analysis.

B. Confusing Pairs

1. GSR vs. GPR

  • Gunshot Residue (GSR): Consists of lead (\text{Pb}), antimony (\text{Sb}), and barium (\text{Ba}) from the primer of the cartridge.
  • Gunpowder Residue (GPR): Comes from unburned or burned smokeless powder (nitrocellulose or nitroglycerin).
  • Key Difference: GSR is primer-based, while GPR consists of gunpowder particles.

2. Organic vs. Inorganic Materials

  • Organic Materials: Contain carbon-hydrogen (CH) structures, e.g., sugar.
  • Inorganic Materials: Lack CH structures, e.g., metals, salts.
  • Key Difference: Carbon presence determines classification.

3. Element vs. Compound vs. Molecular vs. Mixture vs. Alloy

  • Element: Pure substance with identical atoms (e.g., Oxygen, Gold).
  • Compound: Chemically bonded atoms in a fixed ratio (NaCl - Table Salt).
  • Molecule: A group of bonded atoms (\text{O}2, \text{H}2\text{O}).
  • Mixture: A blend of substances without chemical bonding (Air, Soil).
  • Alloy: A mixture of metals (Brass = Copper + Zinc).
  • Key Difference: Elements and compounds are pure substances; mixtures and alloys are physically combined.

4. Protons vs. Electrons vs. Neutrons

  • Protons: Positive charge found in the nucleus.
  • Electrons: Negative charge orbiting the nucleus.
  • Neutrons: Neutral charge found in the nucleus.
  • Key Difference: Charge and location in the atomic structure.

5. Atomic Number vs. Atomic Mass vs. Atomic Weight

  • Atomic Number: Number of protons in an atom.
  • Atomic Mass: Protons + Neutrons (whole number value).
  • Atomic Weight: Weighted average of all isotopes.
  • Key Difference: Atomic number is fixed, while mass and weight vary by isotope.

6. Combustion Ring vs. Abrasion Ring

  • Combustion Ring: Soot/debris caused by close-range gunfire.
  • Abrasion Ring: Skin damage from bullet entry wounds.
  • Key Difference: Combustion ring results from chemical reaction, while abrasion ring is mechanical trauma.

7. Isotopic vs. Ions

  • Isotopes: Same element, different neutron count (Carbon-14 vs Carbon-12).
  • Ions: Charged atoms due to electron loss/gain (Cation (+) / Anion (-)).
  • Key Difference: Isotopes affect atomic mass, while ions change electrical charge.

8. Burned vs. Unburned Powder vs. Soot vs. Stippling

  • Burned Powder: Fully combusted gunpowder.
  • Unburned Powder: Partially combusted powder particles.
  • Soot: Fine black residue from incomplete combustion.
  • Stippling: Powder embedded in skin, causing tiny burns.
  • Key Difference: Soot is airborne, stippling penetrates the skin.

9. Particles vs. Micrometer

  • Particles: Small fragments of matter (GSR residues, dust).
  • Micrometer (μm): A unit of measurement (1 \mu \text{m} = \frac{1}{1000} \text{mm}).
  • Key Difference: Particles describe physical objects, while micrometers measure their size.

10. Quality vs. Quantity Analysis

  • Quality Analysis: Identifies what a substance is (e.g., SEM for GSR).
  • Quantity Analysis: Measures how much of a substance is present (e.g., AAS for metal concentration).
  • Key Difference: Quality tells the type, quantity tells the amount.

YouTube Videos: Gunshot Residue (Ch. 7)

  1. Key Question for Investigator: Ask the potential suspect if they recently shot a firearm to check for GSR left over in their clothing or hands (recently = 3 to 4 hours).
  2. Location of GSR: Most likely located between the thumb and pointer finger.
  3. Distinguishing Suicide vs. Homicide: If GPR is located on the victim's hand, it supports suicide rather than homicide.
  4. Limitations of GSR Test:
    • Needs to be done as soon as possible (washing hands removes GSR).
    • Putting hands in pockets can affect results.
    • The longer the time passes, the less likely a positive GPR test.
  5. Photo Produced: Indiana University of Pennsylvania/Department of Chemistry.

SERATEC Body Fluid (Ch. 8)

  1. PSA: Semi-quantitative test for the detection of human seminal fluid via prostate-specific antigen (found in men).
  2. HemDirect: Highly sensitive qualitative test for the detection of human blood via human hemoglobin.
  3. PMB: Unique duplex test for menstrual blood or peripheral blood; detection of human hemoglobin and d-dimer.
  4. Amylase: Qualitative tests for the detection of human saliva via alpha-amylase.
  5. Amylase Paper:
    • A filter paper kit for the localization of latent saliva stains
    • Application of amylase paper can be combined with semen mapping and other specific human biomarker tests as well as DNA analysis

ALS (Light Spectrum) (Ch. 8)

  • UV: 365-395 nm
  • Blue: 450-495 nm
  • Green: 500-570 nm
  • Infrared: 700-980 nm

DNA Scan Rapid DNA Analysis (Ch. 9-10)

  1. Rapid DNA devices take about 85 minutes to test up to 5 samples simultaneously.
  2. Swab inner cheeks 5 times, 6 times up and down and Cheek should protrude slightly
  3. A second swab should be taken as a reference sample and store it
    • Allows the user to archive and store DNA samples for later use
    • To send the sample to central forensic laboratory for additional analysis
    • To use as a backup in court cases to prove your case
  4. Three steps/measures to guarantee the COC in the rapid DNA process: ?
  5. Three limitations: ?

Chapter 8: Blood

  1. Non-Human Blood vs. Non-Blood Samples
    • Non-Human: Chicken, pig, cow blood.
    • Non-Blood Samples: Marker, Paint, Ketchup.
  2. Erythrocytes vs. Leukocytes Cells
    • Erythrocytes: red blood cells
    • Leukocytes: White blood cells
  3. Presumptive vs. Confirmatory Tests
    • Presumptive: Used to indicate possible blood at the scene
    • Confirmatory: confirm the specific identification of blood
  4. Luminol vs. Seratec Tests
    • Luminol is a chemical compound used in forensic science to detect bloodstains.
    • Seratec offers a range of various rapid, qualitative tests for the forensic identification of various bodily fluids, including human blood, semen, saliva, and menstrual blood.
  5. Hemoglobin vs. Iron Element in Blood
    • Hemoglobin is an iron-rich protein in red blood cells that carries oxygen from the lungs to the rest of the body
    • Iron Element in blood is a component of hemoglobin, a protein that carries oxygen from the lungs to the body's tissues.
  6. Sine (\theta) vs. Co (\theta)
    • In blood spatter analysis, the sine function (\sin \theta) is used to calculate the angle of impact of a blood droplet.
    • In the context of blood, "Co (\theta)" likely refers to the carbon monoxide (CO) diffusing capacity (DlCO), or specifically, the rate of uptake of CO by hemoglobin
  7. False Positive vs. False Negative Tests ~Type I vs Type II Errors
    • False positive or type I errors results in forensic testing occur when a test incorrectly indicates the presence of a substance or characteristic when it is actually absent
    • A false negative or type II errors in forensic science is a test result that incorrectly indicates the absence of a condition or substance when it is actually present
  8. Type AB vs. Type O Blood Types
    • Type AB: (3%) has both A and B antigens called:
    • Type O: (43%): has neither A and B antigens called:
  9. Expiated vs. Cast-off bloodstains
    • Expiated: blood that is expelled from the mouth, nose, or lungs due to breathing, coughing, or other forceful exhalation
    • Cast-off blood stains a type of bloodstain pattern created when blood is projected from a bloody object due to its motion, often in an arc or swing
  10. Spatter/Splash vs. Mist Bloodstains
    • Spatter patterns are created by blood droplets propelled through the air, while non-spatter patterns are formed by blood transferred directly from a source
    • a type of bloodstain pattern that results from blood being reduced to a spray of tiny droplets due to a high force.

Chapter 9-10 DNA Analysis

  1. The Coded-Gene vs. Non-Coded Gene - ?
  2. Genome vs. Chromosome vs. Gene
    • Human Genome = The World
    • Chromosome = CA
    • Gene = a region of DNA that helps determine a characteristic
  3. Locus/Loci vs. Alleles - ?
    • Locus/Loci: Location of Genes
    • Alleles: Types of genes
  4. TA vs. GC Base Pair Rule
  5. The Letter (Sequential Order vs. The Alleles Method)
  6. PCR vs. STR
    • Polymerase Chain Reaction (PCR) can amplify a partial DNA by two steps: PCR amplification process (DNA is repeatedly heated and cooled known as thermocycling) and forensic values (minute quantities, partially degraded, missing parts)
    • STR (short tandem repeats) as Locations/Markers: the current STR’s are the 26 loci on 13 chromosomes on the spacers that contain a short segment (400 bases) with repeated sequences of bases up to 30 times/repeats (DNA sequences of two randomly selected individuals will differ at approx. 1 to 1 billion statistically)
  7. N- DNA vs. F-DNA; M-DNA vs. Y-DNA
    • Nuclear DNA (n-DNA)
    • Familial DNA (f-DNA)
    • Mitochondrial DNA (m-DNA)
    • Y- chromosome DNA (y-DNA)
  8. CODIS vs. NGI vs. Forensic Genealogy
    • CODIS: combined DNA index system (13mil offenders, 2.6mil arrestees, 0.7mil scenes DNA profiles unknown)
    • NGI: next generation information (palm, iris, facial)
    • Forensic Genealogy: where law enforcement uses DNA analysis and traditional genealogy research to solve crimes, often cold cases, by identifying potential suspects or victims
  9. Genotyping vs. Phenotyping
    • Genotype: Pairing Parents
    • Phenotype: Genetic + Environment
  10. Degradation vs. Cross-Contamination vs. Mutation
    • Degradation: the breakdown of organic matter by living organisms
    • Cross-Contamination: the unwanted transfer or material or foreign substances from one piece of evidence to another (ex. Crime scene technician sneezes on piece of evidence)
    • Mutation: a change in an organism’s genetic material DNA (exposure to external factors like radiation or chemicals, viral infections, or an error during DNA replication)