Last two lectures of criminalistics

Document examination

This applies scientific methods to analyze questioned documents. Examiners use visual inspection and instrumental techniques to authenticate documents, detect alterations, and compare handwriting.

Biomechanics, learned habits, neurological pathways

Handwriting is shaped by…

Letter formation

This handwriting character affects shape, slant, and size. Includes letter connections and stroke direction.

Writing dynamics

This handwriting character affects speed, spacing, pressure, and overall control/dexterity.

Document arrangement

This handwriting character affects margin alignment, line spacing, and page orientation.

Position, fatigue, stress, speed, writing instrument, and surface

Variation in handwriting is influenced by…

Collecting handwriting exemplars

Content requirements:

• Include same words/letter combinations

• Allows direct comparisons

Non-contamination protocol:

• Do NOT show questioned document

• Avoid giving spelling/punctuation help

• Prevents imitation

Material similarity:

• Match pen, ink, and paper

• Writing surface affects results

Sufficient quantity:

• Collect multiple samples/pages

• Captures natural variation

• One sample is not enough

Mechanical defects, toner distribution, registration marks

Label the characteristics of printing devices…

__________ _______:

• Worn/damaged components

• Scratches, spacing issues

• Repeatable patterns

_____ __________:

• Density variations

• Streaking or fading

• Cartridge-specific patterns

__________ _____:

• Alignment errors

• Repeated smudges

• Consistent positioning issues

Laser printing

This digital technology creates toner fusion patterns. heat-based printing with distinct microscopic features.

Digital photocopying

This digital technology creates compression artifacts and pixel patterns. Digital noise signatures.

Inkjet printing

This digital technology creates ink droplet patterns, nozzle defects, edge detail, and ink bleeding.

Alterations

(Questioned Documents)

Adding or changing information

Erasures

(Questioned Documents)

Removing writing (mechanical or chemical)

Obliterations

(Questioned Documents)

Covering or hiding original content

Infrared analysis

This technique helps reveal ink differences not visible to the naked eye. Some inks will become transparent while others remain visible. Reveals hidden or altered writing. Can reveal obliterations in questioned documents.

Identifying erasures

How to detect:

• Use microscopy

• Examine under direct and oblique light

What to look for:

• Disturbed or broken fibers

• Surface roughness

• Loss of original texture

• Indentations or irregularities

Damage remains even if writing is overwritten.

Indented writing

Impressions from previous pages. Revealed using electrostatic detection apparatus (ESDA)

Faded ink

Lost or weakened writing. Enhanced with multispectral imaging.

Charred documents

Fire damage materials recovered with careful handling and imaging.

Watermark analysis

Identifies paper source & age. Helps detect authenticity issues.

Image enhancement, multispectral imaging, automated comparison

Label the image processing applications…

_____ ________:

• Adjusts contrast & brightness

• Removes background noise

• Improves text clarity

__________ ______:

• Uses multiple wavelengths (UV → IR)

• Reveals hidden/altered writing

• Different inks respond differently

________ _________:

• Compares handwriting features

• Measures stroke characteristics

• Identifies pattern similarities

Visual spectrophotometry, thin-layer chromatography, raman spectroscopy, hyperspectral imaging, x-ray fluorescence, laser spectroscopy

Label the ink & paper comparative methods…

______ ____________:

• Non-destructive

• Measures light absorption

• Creates ink “spectral profiles”

____-_____ _____________:

• Separates ink components

• Reveals dye composition

• Requires small samples

_____ ________:

• Non-destructive

• Provides molecular “fingerprints”

• Identifies ink composition

_______ ______:

• Captures many narrow wavelength bands

• Detects ink differences

• Reveals subtle alterations

_-___ ___________:

• Identifies elemental composition

• Analyzes ink & paper

• Useful for dating & authenticity

_____ __________:

• Provides molecular information

• Non-destructive analysis

• Identifies material differences

Serology

What is the study of biological fluids such as blood, semen, and saliva? This can place someone at a scene, support or refute statements, and lead to DNA analysis.

Semen

These three tests are presumptive for which biological fluid?

1. Acid Phosphatase (AP)

• Fast, sensitive

• Purple color = positive

2. PSA (p30)

• More specific than AP

• Still considered screening in forensics

3. Microscopy (sperm cells)

• Can visually identify sperm

• Not always present (vasectomy, degradation, etc)

Blood

These four tests contain peroxidase-like activity of hemoglobin and are presumptive for which biological fluid?

1. Kastle-meyer (phenolphthalein)

• Pink color = positive

2. Luminol

• Blue glow in the dark

• Great for hidden/cleaned blood

3. Leucomalachite Green

• Green color change

4. Hemastix

• Quick tests trips

Individualizing bloodstains

Step 1:

• Is it human? Use species-specific tests (antibodies)

• Confirms: Human vs animal

Step 2:

• DNA analysis (STR profiling)

• Creates a genetic profile

Why DNA is powerful:

• Can match blood to one individual

• Extremely high accuracy (often 1 in billions)

DNA

This is your genetic blueprint and is found in almost every cell in your body. It carries instructions for growth, development, body function, and reproduction. It is unique to each person (except identical twins) and can identify individuals, link people to evidence, and exclude suspects.

Nuclear DNA

This type of DNA is shaped like a twisted ladder (two strands twisted together). It is made of repeating units (building blocks) of sugar, phosphate, and a base (A, T, C, G). Base pairs in a specific way: A — T and C — G. The order of base pairs is what makes DNA different between people.

Gene

A small section of DNA that contains instructions and codes for a protein or functional RNA.

Think: a single recipe in the instructions manual.

Chromosome

A package of DNA inside the nucleus that holds many genes. Humans have 23 pairs (46 total).

Locus

The specific location/marker of a gene on a chromosome. Like an address for a gene.

Allele

What is the specific value at a locus? We have two at each locus one from mother and one from father. Reported as numbers.

DNA tandem repeats

Short DNA sequences that repeat back-to-back (ex. GATA GATA GATA). The number of repeats varies between people which is useful for DNA identification. We analyze these repeats at specific locations (STR loci). The combination of repeats = a person’s DNA profile.

Short Tandem Repeats (STRs)

These are specific locations on DNA (loci) that contain short repeating sequences (2-6 base pairs). Gold standard for forensic DNA profiling.

Advantages include…

1. High sensitivity (works well with small or degraded samples)

2. High discrimination

3. Rapid analysis

4. Database compatible

Extraction, quantitation, amplification, separation, and data analysis

What are the steps in forensic DNA analysis?

DNA extraction (purification)

The goal of this step of DNA analysis is to get clean DNA out of cells for analysis.

Step 1: Cell lysis

• Breaks open cells

• Releases DNA from the nucleus

Step 2: Protein removal

• Removes proteins and debris

• DNA sticks to a silica membrane

Step 3: DNA precipitation

• Washes away impurities

• DNA stays attached

Step 4: Elution

• Release (collect) purified DNA

• DNA is now ready to analyze

DNA Quantitation

This step of DNA analysis measures how much DNA is in a sample. It ensures the right amount of DNA goes into PCR. Too little DNA will cause weak results and too much DNA will cause messy/overloaded data.

Real-time PCR (qPCR)

This DNA quantitation technique measures DNA during amplification in real time. It uses fluorescent probes to track DNA amount. Tells us DNA concentration, human-specific DNA, male DNA (Y-target), degradation level, and presence of inhibitors. Works well with trace samples.

DNA amplification

This step of DNA analysis utilizes the polymerase chain reaction (PCR), an elegant molecular biology technique that produces millions of copies of specific DNA regions.

Thermal cycling process:

1. Denature (94-96 degrees C) - Heat separates double-stranded DNA into single strands

2. Anneal (50-65 degrees C) - Primers bind to complementary target sequences

3. Extend (72 degrees C) - DNA polymerase synthesizes new DNA strands

The cycle repeats 28-32 times, doubling DNA with each cycle.

Primer, template DNA, dNTPs, DNA polymerase, and fluorescent dyes

List the essential PCR components

DNA separation

This DNA analysis technique is the process of sorting amplified DNA fragments by size so they can be identified and used to generate a DNA profile. This is typically done using capillary electrophoresis, where an electric field pulls negatively charged DNA through a polymer-filled capillary, allowing fragments to be separated with high precision based on size.

1. Injection - DNA is loaded into a thin capillary tube

2. Separation - Electric field pulls DNA through polymer. Smaller fragments travel faster than larger ones.

3. Detection - Laser detects fluorescent labels and produces a graph (electropherogram)

STR typing

This process combines DNA extraction, PCR amplification of specific loci, and capillary electrophoresis to separate DNA fragments by size. The resulting pattern of peaks represents the individual’s unique genetic profile at each STR locus examined.

Power of STRs

The true strength of STR analysis lies in multiplexing — simultaneously analyzing multiple STR loci to create highly discriminating DNA profiles that can individualize evidence with extraordinary statistical certainty.

New STR kits

What’s improved?

• Analyze more STR loci (15-24+) at once

• Use multiple dye colors to detect many fragments simultaneously

Why does this matter?

• Higher discrimination

• Better mixture interpretation

• Works better with degraded DNA

• Compatible with national databases (CODIS)

More loci = more power to distinguish between individuals.

Product rule

We combine multiple STR loci to calculate how rare a DNA profile is. STR loci are independent of each other → one locus does not affect another.

Multiply the frequency of each allele/genotype

Ex…

• Locus 1: 1 in 10

• Locus 2: 1 in 20

• Combined: 1 in 200

Combined DNA index system (CODIS)

This is the FBI’s national DNA database system and is used to compare DNA profiles across labs. Convicted offenders, arrestees, crime scene evidence, missing persons, and unidentified remains will all be found in this database.

Amelogenin marker

This is present on both X and Y chromosomes. Included in most STR kits and allows sex determination during DNA profiling.

Sex identification:

• Female (XX): 1 peak

• Male (XY): 2 peaks

Y-STRs

These STRs are located only on the Y chromosome. They are passed from father to son and target male DNA in mixtures. They are useful when female DNA overwhelms male DNA and can detect small amounts of male DNA. Inherited is unchanged along the paternal line. Males in same family share similar ____ profiles. Useful for kinship and genealogy.

Mitochondrial DNA

This type of DNA is useful when nuclear DNA is degraded or absent. Examples include hair shafts, bones, and teeth. This DNA is not located in the nucleus but contains many copies per cell (easier to recover). It has a circular DNA structure. It is inherited solely from the mother which meals all maternal relatives share the same ____ profile.

Collection of DNA evidence

Clothing collection:

• Collect from victim and suspect

• Package each item in a separate paper bag

Dried stains:

• Use slightly moistened swab (distilled water)

• Air dry completely before packaging

Individual packaging:

• Package items separately

• Paper, NOT plastic

• Plastic traps moisture → DNA degradation

Reference samples:

• Collect reference samples from known individuals

• Buccal swabs or blood samples

• Used for comparison

Packaging biological evidence

1. Air dry first - prevents mold and bacterial growth

2. Use paper, NOT plastic - plastic traps moisture -→ DNA degradation

3. Package separately - prevents cross contamination

4. Seal & label properly - case info, initials, date/time

5. Maintain chain of custody

6. Store properly - keep cool, dry, and refrigerate/freeze if needed

Sexual Assault evidence

Common evidence collected:

Swabs:

• External genital, vaginal/cervical, rectal

• Oral swabs

• Bite marks & contact areas

Reference samples:

• Buccal swab

• Blood sample

• Head & pubic hair

Trace evidence:

• Fingernail scrapings/clippings

• Pubic hair combings

Clothing/items:

• All clothing (outer + undergarments)

• Bedding or objects from the scene

Toxicology

• Urine sample (drug/alcohol testing)

4-6, 48, 72, 3-6

1. Intact sperm with tails can be detected for _-_ hours.

2. Seminal acid phosphatase enzyme can persist for <__ hours.

3. Prostate-specific antigen (PSA) are detectible for <__ hours.

4. Sperm heads without tails can remain detectable for _-_ days.

Paint

This evidence is a powerful forensic tool, especially in forensic hit-and-run evidence.

• Layered structure → unique to each source

• Chemical composition → helps identify origin

• Can link suspects, vehicles, and crime scenes

• Each tiny fragment can provide strong associative evidence

Binder

Holds paint together and helps it stick to surface

Pigment

Provides the color and opacity of paint. Adds durability (e.g. corrosion resistance.

Solvent

Keeps paint liquid for application. Evaporates as paint dries.

Additives

Improves performance (control drying, flow, and UV stability) for paint.

Brushing

A manual paint application for small areas and detail work.

Rollers

A paint application for large, flat surfaces. Has fast coverage.

Spraying

A paint application for smooth, even coating. Good for complex shapes.

Dipping

A full immersion paint application for complete, uniform coverage.

Electrodeposition

A paint application that uses an electrical current for a durable, uniform coating (automotive).

True

True or false

Each paint layer serves a specific function and together they create a unique fingerprint.

Paint collection

Document:

• Photograph evidence in place

• Record location & context

Use proper tools:

• Clean tweezers or scalpel

• Avoid contamination

• Preserve layer structure

Collection sufficient sample:

• Gather enough material

• Keep layers intact

Package seperately:

• Use rigid containers

• Prevent damage or mixing

Color, texture, layer sequence, thickness, decorative elements, pigment analysis, defects

Label the paint parameters:

_____: Visual & instrumental comparison

_______: Surface finish & application patterns

_____ ________: Order of layers (substrate → topcoat)

_________: Individual & total layer thickness

________ ________: Metallic flakes, special pigments

______ _______: Particle size, shape, distribution

_______: Unique imperfections (individualizing features)

Pyrolysis GC

This analysis method is useful for determining binder composition in paint.

IR spectroscopy

This analysis method is useful for determining chemical identification of paint.

Microscopy

This analysis method is a visual screening which examines color, texture, and layer structure of paint.

SEM-EDS

This analysis method is useful for determining elemental composition and analyzes pigments & additives in paint.

Ford Model Pyrogram

This pyrogram shows characteristic peak patterns unique to Ford’s acrylic enamel formulation, with distinct thermal decomposition products.

Chrysler Model Pyrogram

This pyrogram displays peak distribution, demonstrating how manufacturers use proprietary binder formulations that can be distinguished forensically.

Paint collection

Documentation:

• Photograph in place (with scale)

• Record location & context

Rigid packaging:

• Use pillboxes or vials

• Prevent crushing, smearing, or contamination

• Keep questioned vs known apart

Precise labeling:

• Include case #, date, and location

• Add collector & description

Cross section

What is this type of paint cut?

Thin peel

What is this type of paint cut?

Wedge Cut

What is this type of paint cut?

Stair step

What is this type of paint cut?

Electrocoat, primer, basecoat, clearcoat

Label the different type of automotive paint types…

__________:

• Applied directly to metal

• Provides corrosion resistance

______:

• Smooths surface imperfections

• Prepared for color layers

________:

• Provides color & special effects

• Contains pigments (metallic flakes)

_________:

• Transparent top layer

• Adds gloss, UV protection, and scratch resistance

Alkyd resins, acrylic polymers, epoxy resins, polyurethanes

Label the different type of paint binders…

_____ ______:

• Common in household paints

• Traditional oil-based polymers

_______ ________:

• Common in modern automotive paints

• Good color retention & weather resistance

_____ ______:

• Used in industrial/marine coatings

• Strong adhesion & chemical resistance

_____________:

• High-performance coatings

• Durable, abrasion-resistant (often clearcoats_

Inorganic pigments

These pigments provide opacity & stability. Examples include titanium dioxide (white), iron oxides (yellow, brown), and chromium oxides (green).

Organic pigments

These pigments provide bright, vibrant colors. Examples include azo dyes, phthalocyanines (blue/green), quinacridones (red/violet).

Plasticizers, UV stabilizers, flow agents, anti-settling agents

Label the functional additives (paint)…

_________: flexibility

__ _________: prevent degradation

____ ______: smoother application

____-_______ _____: keep pigments mixed

Issues in paint interpretation

Environmental weathering:

• Sunlight, moisture, pollutants alter paint

• Causes fading, chalking, oxidation

• Must compare aged vs fresh samples carefully

Repair and repaint complexity:

• Adds non-original layers

• May not match factory finish

• Can complication or help comparison

Contamination concerns:

• Dirt, oil, rust can obscure color/layers

• May interfere with analysis

• Cleaning must preserve original structure

Paint data query (PDQ)

This database contains over 70,000 automotive paint samples, helping investigators narrow vehicle possibilites based on layer structure and composition.

Soil

This evidence is common at crime scenes and easily transferred between people, objects, and locations. It can be distinguished by color, texture, and composition. Even simple side-by-side comparison can differentiate from different locations. Provides valuable trace evidence linking suspects to scenes.

Points of comparison for soil

• Minerals (type and abundance)

• Organic material (plant remains, microbes)

• Grain size and texture

• Color & layering

• Artificial debris (glass, fibers, pollutants)

Sandy, clay, silt, loam

Label the soil types…

_____ soil:

• Large particles, gritty texture

• High drainage, low nutrient retention

____ soil:

• Very fine particles, smooth texture

• Poor drainage, high nutrient retention

____ soil:

• Medium particles, smooth feel

• Moderate drainage, fertile

____ soils:

• Mix of sand, silt, and clay

• Balanced properties (ideal soil)

Granular

This soil structure…

• Small rounded pieces

• Common at surface

• Good for plant growth

• High permeability

Blocky

This soil structure…

• Irregular blocks

• Found in subsoil

• Moderate drainage

Prismatic

This soil structure…

• Vertical columns

• Clay-rich soils

• Water moves slowly

• Moderate permeability

Platy

This soil structure…

• Thin, flat layers

• Compacted soils

• Poor water movement

NIST guidelines for soil analysis

Documentation:

• Record how & where soil was collected

• Maintain chain of custody

Analysis protocols:

• Use standardized methods & instruments

• Examples: microscopy, chemical tests

Comparison standards:

• Compare to known/reference samples

• Use statistics to support conclusions

Inorganic minerals

This part of soil gives it its structure. Ex… sand, quartz, feldspar

Organic matter

This part of soil affects colors & nutrients. Ex… decaying plants & animals

Microorganisms

This part of soil can link it to a location. Ex… bacteria, fungi

Human (anthropogenic) debris

This part of soil contains strong forensic clues. Ex… glass, paint, fibers

Soil reference samples

• Collect from multiple locations

• Include the exact site + surrounding area (~100ft)

• Used for comparison late

• DO NOT remove soil from items

• Package items as is

Munsell Color System

This is a standardized way to describe soil color. It removes subjective descriptions “brownish”.

Hue:

• Red, yellow, brown

• EX: 10YR, 5R

Value:

• How light or dark?

• Scale: 0=black → 10=white

Chroma:

• How intense?

• Dull → bright color

• Low = grayish, high = vivid

Stereomicroscopy (soil)

• 10-50x magnification

• Examines color differences, particle size, and visible debris (glass, paint)