Forensic Science: Key Concepts, Crime Scene Protocols, Evidence Types, and Investigation Techniques

Purpose of Forensic Science:

To use science to help resolve legal matters

Role of Forensic Investigator:

1. Collects and examines physical evidence

2. Reports to law enforcement

3. Possibly testifies in court

Tools of the Forensic Investigator:

1. Ability to observe, interpret, and report findings

2. Ability to identify the evidence, document it, and determine its significance

Role and Responsibilities of Forensic Scientists:

- Observation and application

- Communication

- Deductive Reasoning

Observation and application of Forensic scientists

1. Find evidence

2. Collect data

a. Qualitative data

b. Quantitative data

3. Analyze data

Communication of forensic scientists

1. Convince a jury that evidence is:

A. Scientific

B. Reliable

C. Valid

D. Sufficient

Deductive reasoning of forensic scientists

Using the scientific method and the claim-evidence-reasoning model

Scientific method:

1. State the problem or question

2. Propose a hypothesis

3. Conduct an experiment

4. Collect data

5. Analyze data

6. Draw a conclusion

Claim-Evidence-Reasoning Model:

1. Make observations

2. Determine what question you want to answer

3. Make a claim and an assertion

4. Provide evidence

5. Provide reasoning or justification

Observation

1. Gathering information through the senses

a. Sight, taste, hearing, smell, touch

2. Done largely without thinking

Perception

1. Interpreting sensory observations

Not always accurate

a. Does not always reflect reality

2. Understanding limitations

Helps improve observation skills

Observations made by witnesses:

1. Perception of witnesses can be faulty

2. Emotional states influence perceptions

3. Eyewitness accounts can be valuable evidence

4. Eyewitness accounts can be valuable evidence

5. Many factors affect accuracy

Eyewitness Accounts

1. Vary considerably from person to person

2. Require discrimination between fact and opinion

3. Used to sequence the events

4. The Innocence Project

5. Found that eyewitness identification contributed to up to 70 percent of wrongful convictions

Ways to improve observation skills:

1. Systematically examine the environment

2. Turn off filters; act like data-gathering robots

3. Avoid looking for patterns

4. Concentrate on gathering information

5. Leave interpretation until later

6. Write down and photograph as much as possible

Conducting Interviews

- Separate witnesses as soon as possible

- Help witnesses reconstruct what happened

- Provide minimal guidance

- Avoid interjecting biases

- Write down observations

- Ask questions to draw out details

Identifying a truth or a lie

- A true account is consistent each time it's told

- Lies are difficult to repeat exactly the same

- Methods to identify truths or lies

- Have witness repeat story several times

- Ask witness to recount story in reverse order

- Distract interviewee with questions

The Innocence Project

An organization staffed by lawyers and law students who reexamine cases and provide legal assistance to convicts when there is a probability that serious errors occurred in their prosecution.

Goals of a Crime-scene Investigation

- To recognize, document, photograph, and collect evidence at the crime scene

- Solving the crime depends on piecing together the evidence to form a picture of what happened at the crime scene

- Evidence must remain valid and reliable; in response to the 2009 National Academy of Sciences report calling for more scientific evidence testing, Scientific Working Groups (SWGs) were formed and later evolved into the Organization of Scientific Area Committees (OSACs) to standardize and improve protocols.

Professionals included on a crime scene

Police officers, district attorney, crime scene investigators (CSIs), medical examiners (coroners) detectives, and specialists

Police Officers

Typically the first responders who secure the area and ensure public and officer safety.

District Attorneys

Determine legal requirements, such as obtaining search warrants.

Crime Scene Investigators (CSIs)

Document the scene, take photographs, sketch layouts, and systematically collect evidence.

Medical Examiners (Coroners)

Examine the deceased to establish the cause and manner of death.

Detectives

Interview witnesses, pursue leads, and reconcile evidence findings with witness statements.

Specialists

Experts (such as entomologists, toxicologists, or botanists) brought in when specific evidence requires specialized analysis.

Locard's Principle of Exchange

- Whenever two people come into contact with each other or with an object, a physical transfer occurs

- The second part of this principle states that the intensity, duration, and nature of the entities in contact determine the extent of the transfer (e.g., more transfer occurs during a physical fight than from a brief brush-by).

Trace Evidence

Transferred materials (e.g., pet hair, fibers, fingerprints, blood drops, soil, paint chips, broken glass)

Direct Evidence

Firsthand observations such as eyewitness accounts or police dashboard video cameras

Examples of direct evidence

- A witness states that she saw a defendant pointing a gun at a victim during a robbery

- In court, this involves testimony by a witness about what that witness personally saw, heard, or did

- Confessions

Circumstantial Evidence

Evidence that implies a fact but does not prove it. No one other than the suspect and/or victim actually knows when this term is produced

Two types of circumstantial evidence

Physical and biological

Physical Evidence

Includes fingerprints, footprints, shoe prints, tire impressions, and tool marks

Biological Evidence

Includes DNA in tissue, bodily fluids, hair, plants, pollen, and natural fibers

Class Evidence

Narrows an identity to a group of persons or things

Example of class evidence

ABO blood type of a sample of blood from a crime scene tells us that one of many persons with that blood type may have been there

Individual Evidence

Includes a unique combination of characteristics that it could only belong to one person or thing, such as a fingerprint or DNA

The Seven S's of Crime Scene Investigation

1. Securing the scene

2. Separating the witnesses

3. Scanning the scene

4. Seeing the scene

5. Sketching the scene

6. Searching for evidence

7. Securing and collecting evidence

Securing the scene

- Is the responsibility of the first responding law-enforcement officer

- The safety of all individuals in the area is the first priority

- Preservation of evidence is the second priority

- The first officer on the scene keeps a security log of all those who visit the crime scene

Separating the witnesses

- Witnesses must not be allowed to talk to each other

- Crime-scene investigators will compare the witnesses' accounts of the events

- Witnesses are separated so that they do not work together to create a story (collusion)

- Interviewing the witnesses and asking specific questions

Questions to ask the witnesses when separating them

- When did the crime occur?

- Who notified law enforcement?

- Who is the victim?

- Can the perpetrator be identified?

- What did you see happen?

- Where were you when you observed the crime scene?

Scanning the scene

- Forensic CSIs determine where photos should be taken

- A determination may be made of a primary crime scene and a secondary crime scene, and priorities assigned regarding examination

Seeing the scene

- CSIs capture overall and close-up photos with and without a measuring ruler.

- Triangulation should be included in the photos

Triangulation

A technique used to record the location of evidence from two fixed reference points. Close-ups and photos of any evidence and remains from varying distances should be taken

Sketching the scene

- All objects should be measured from two immovable landmarks

- On the sketch, north should be labeled, and a distance scale should be provided

- Any other objects in the vicinity of the crime scene, such as doors, windows, and furniture, should be included in the sketch

Searching for evidence

- Types of search patterns are used depending on the size of the area to be searched and the number of investigators

- Single investigators might use a gridded, linear, or spiral pattern

- A group of investigators might use a linear, zone, or quadrant pattern

Securing and collecting evidence

- All evidence needs to be properly packaged, sealed, and labeled

- Specific procedures and techniques for evidence collection and storage must be followed

- Liquids and arson remains are stored in airtight, unbreakable containers

- Moist biological evidence is stored in breathable containers so that the evidence can dry out, reducing the chance of mold contamination

- After the evidence is allowed to air dry, it is packaged in a paper bindle, a folded paper used to contain trace evidence

- The bindle (also called a druggist's fold) can then be placed in a plastic or paper container

- This outer container is then sealed with tape and labeled with the signature of the collector written across the tape

- The size of the paper bindle depends on the size of the evidence

- If the evidence is small, the paper bindle can be constructed from a sheet of paper

- If the evidence is large, the bindle might be constructed from a large sheet of wrapping paper

- Evidenced to be logged

Steps that describe how to prepare a paper bindle for evidence collection

1. Choose the appropriate size sheet of clean paper for the bindle

2. Crease the paper as shown

3. Place evidence in the location shown by the X

4. Fold the left and right sides in

5. Fold in the top and bottom

6. Insert the top flap into the bottom flap; then tape the bundle closed

7. Place the bindle inside a plastic or paper evidence bag. Fold the bag closed

8. Place a seal over the folded edge of the evidence bag

9. Have the collector write their name over the folded edge

What should be in the evidence log

- Case number

- Item inventory number

- Description of the evidence

- Name of the suspect

- Name of victim

- Date and time of recovery

- Signature of person recovering

- Signature of person recovering the evidence

- Signature of any witnesses present during collection

Steps to map the outdoor crime scene

1. Establish the collection site

2. Locate a datum point

3. Mark evidence collection limits

4. Measure and mark evidence positions

Datum Point

Identify a permanent, immovable landmark (e.g., a tree or the corner of a building)

Subdatum Point

Using a compass, set a northern boundary corner at least 1 meter away from any evidence, mark it with a rebar or stake, and calculate the distance and angle from the datum

Perimeter Corners

Establish the remaining corners of the rectangular collection site using the subdatum point as a reference

Traingulation/Perpendicular Measurements

Map each piece of evidence by measuring its perpendicular distance to the North-South and East-West baseline perimeter lines

Analyzing the evidence

- A forensic lab processes all of the evidence that was photographed, documented, and collected at the crime scene

- The laboratory results are sent to the lead detective

- The detective examines the evidence and compares it to eyewitnesses' statements to check on the reliability of their accounts

- Evidence is evaluated to be scientific, sufficient, reliable, and valid

- The Department of Justice provides guidelines for expert witness testimony

- Evidence should be based on quantitative and statistical references and databases and should avoid inferences and subjective personal experiences

Crime Scene Reconstruction

Forming a hypothesis of the sequence of events from before the crime was committed through its commission

Commonly staged crime scenes

- Arson to cover other crimes

- Murder staged to look like suicide

- Burglary to collect insurance money

Determining if a crime scene is staged

- Initially treat all death investigations as homicides

- Are the type(s) of wounds on the victim consistent with the suspected weapon employed?

- Could the wounds be easily self-inflicted?

- Establish a victim profile

- Evaluate behavior before the event

- Corroborate statements

- Reconstruct the event

Advances in crime scene investigations

- Surveillance cameras and facial recognition programs have been very helpful in reconstructing accidents and identifying who was present and when they were present

- The use of ground-penetrating radar is used to locate bodies and hidden evidence

- Three-dimensional stationary camera systems like the OSCR 360 allow investigators to record crime scenes in real time and document the location of evidence for later viewing by juries

Jon Benet Rasmey Case

Key forensic evidence was lost because the crime scene was not properly secured

Mammalian species have two types of hair

1. Long and stiff hair

2. Fine, fuzzy, or wooly hair

Value of hair as evidence

Trace transfer and durability

Trace Transfer in hair

Easily adheres to surfaces (clothes, blankets, carpets) and transfers readily to victims, suspects, or crime scenes

Durability in hair

A tough outer keratin structure resists decomposition, remaining viable long after soft tissues decay

Classification of class evidence of hair

Hair without root/follicle provides characteristics (color, shape, medulla pattern) consistent with groups rather than a specific individual

Classification of individual evidence of hair

Hair with an attached root/follicle yields nuclear DNA unique to an individual

Late 1800s on hair

Hair recognized as trace evidence in criminal investigations; Alfred Swaine Taylor and Thomas Stevenson included a chapter on forensic hair analysis in The Principles and Practice of Medicale Jurisprudence (1883)

1910 on hair

Victor Balthazard and Marcelle Lambert published Le Poil de l'Homme et des Animaux, detailing microscopic studies of human and animal hair

1934 on hair

Dr Sydney Smith first utilized the comparison microscope for side-by-side comparisons of crime-scene hairs with known reference standards

Late 20th Century to Present on hair

Adoption of chemical profiling, Neutron Activation Analysis (NAA), mitochondrial DNA (mtDNA), and nuclear DNA typing

2015 Review on hair

The FBI, DOJ, Innocence Project, and NACDL reported that at least 90% of reviewed cases involving microscopic hair comparison contained examiner testimony errors, spurring stricter reliance on objective DNA and instrumental methods

Three Stages of the development of Hair

Anagen stage, catagen stage, and telogen stage

Anagen Stage

A period of active growth where the cells around the follicle are rapidly dividing and depositing materials within the hair, lasting approximately 1000 days, making up 80-90% of all human hair

Catagen Stage

Follows as the hair stops growing and the follicle recedes as the blood supply is reduced, making up about 2% of all hair growth and development

Telogen Stage

During this stage, the hair follicle is dormant or resting, and hairs are easily lost. At the end of this stage, the blood supply reconnects to the follicle, and another anagen phase begins. This stage makes up approximately 10-18% of all hairs

Hair Function

Thermoregulation (keeping warm or cool), environmental hazard protection, tactile sensation, and animal camouflage

Biological structures of hair

Follicles and hair shafts

Follicle

A club-shaped epidermal indentation containing the dermal papilla, blood-supplying capillaries, and actively dividing matrix cells with nuclear DNA. Associated with a sebaceous gland (containing oils) and erector muscles

Hair Shaft

Non-growing dead strand composed of keratin chains linked in helices

Shaft Cross-Section (Outer to Inner)

Includes cuticle, cortex, and medulla

Cuticle

Protective, scaly outer layer made of overlapping transparent cells

Cortex

Thickest middle portion in humans; contains pigment granules (melanin) determining hair color

Medulla

Central canal running down the hair axis (can be continuous, interrupted, fragmented, solid, or absent)

Macroscopic & Microscopic Human Hair

Varies in cross-sectional shape (circular, oval, flat), texture, color, and medullary pattern (continuous, interrupted/intermittent, fragmented/segmented, solid, or absent

Continuous medulla pattern of hair

One unbroken line

Interrupted (intermittent) medulla pattern of hair

Pigmented line broken at regular intervals

Fragmented or segmented medulla pattern of hair

Pigmented line unevenly spaced

Solid medulla pattern of hair

Pigmented areas filling both the medulla and the cortex

No medulla pattern of hair

No separate pigmentation in the medulla

6 Types of hair on the human body

Head, eyebrows, eyelashes, beard, moustache, underarm, body, and pubic

Head Hair

Uniform diameter, circular to elliptical cross section

Eyebrows and Eyelashes

Circular cross section with distinct tapered tips

Beard and Moustache hair

Coarse, thick, often triangular in cross section, sometimes featuring a double medulla

Underarm Hair

Straight, less buckled, long, fine, and sharp

Body Hair

Can be elliptical or triangular

Pubic Hair

Oval to triangular cross section; commonly displays marked diameter variations and buckling

Cosmetic Treatments

Bleaching oxidizes melanin throughout the cortex and distorts cuticle scales, displaying a sharp line of demarcation. Artificial dyes deposit pigment across the cuticle and cortex, creating an unnatural, painted appearance. Peroxide in bleach can also damage mtDNA

Growth Rate & PMI

Human head hair grows at roughly 1.3cm per month (0.44mm per day), allowing analysts to estimate the time elapsed since the last cosmetic coloring treatment

mtDNA

mitochondrial DNA

European Characteristics of Hair

- Appearance: Generally straight or wavy

- Pigment Granules: Small and evenly distributed

- Cross section: Oval or round of moderate diameter with minimal variation

- Other: Color may be blond, red, brown, or black

Asian Characteristics of Hair

- Appearance: Straight

- Pigment granules: Densely distributed

- Cross section: Round with large diameter

- Other: Shaft tends to be coarse and straight; thick cuticle; continuous medulla; color black