Lesson 1.1: Investigating the Scene

Decedent

legal term for a person who has died

Link Method

used to find linked associations between evidence

• investigators form logical links between crime scene activity and the likely places additional evidence could be found at the scene

based on the notion that one piece of evidence leads to another

works with large and small, indoor and outdoor crime scenes

Line (Strip) Method

search team members are arranged parallel to one another

• proceed in straight paths

used in large, outdoor scenes

Grid Method

searchers first follow a straight line path (similar to line method)

once the pattern is complete, investigators configure a path perpendicular to the original direction

used in large, outdoor scenes

Zone Method

teams are assigned small zones for searching

other search methods are paired with the zone method

used on crime scenes with readily definable zones (ex: houses/buildings)

Spiral Method

used on scenes with no physical barriers (ex: open water)

• Outward Spiral: members begin at critical point of scene

• Inward Spiral: members begin at the outer edge of the scene

Wheel/Ray Method

investigators start from a critical point and travel outward along many straight lines

used on small, circular scenes

Point of Origin

an item/location from which a forensic scientist takes all their measurements in order to make an accurate crime scene sketch

the measurements typically start from the point of origin to a critical piece of evidence

Persons of Interest

someone who law enforcement thinks may have information related to a possible crime

Physiological Responses

involuntary reactions to stimuli that can be felt, detected, and/or measured

Polygraph Tests

commonly known as lie detector tests

sometimes used in forensic cases to help determine the truthfulness of someone who may be connected to a possible crime

• also used in employment screenings

use multiple sensors and computer software to record and display data

seniors record physiological changes in;

• heart rate

• respiration rate

• blood pressure

• skin conductivity

• perspiration/sweat

Heart Rate

a measure of cardiac activity usually expressed in numbers of beats per minute (bpm)

one of the key vital signs used to assess overall health

each heartbeat sends blood though our vessels to our tissues, delivering oxygen and taking away carbon dioxide

• high bpm: body working hard to meet oxygen demands

• low bpm: body may not get enough oxygen to function

Blood Pressure

the pressure exerted by the blood upon the walls of the blood vessels

• arteries: a type of blood vessel - will bulge up and expand its walls in reaction to a surge of blood

Pulse

the rhythmic expansion and recoil of arteries resulting from heart contraction

Respiration Rate

the number of breaths an organism takes per minute

key vital sign

1 breath = inhalation + exhalation

our respiratory system works with the cardiovascular system to take in oxygen, deliver it to cells, and remove carbon dioxide

Skin Conductivity

how the amount of sweat produced impacts the ability to conduct electricity

“What are some activities that can affect your heart rate and respiratory rate?”

Exercise —> increases bpm

Stress —> increases bpm

Illness —> increases heart rate

Meditation —> slows respiratory rate

Vital Signs

measurements that indicate the state of a patient’s essential body functions

• pulse rate

• temperature

• respiration rate

• blood pressure

Baseline/Control

data that serves as a reference on how the subject responds without the independent variable

polygrapher establishes baseline by asking the subject a series of yes/no questions with known answers

Independent Variable

the variable that the researcher intentionally changes to determine its influence on the dependent variable

Dependent Variable

the variable being measured and whose value is influenced by another variable

Experimental Design

1. identify the question

2. make a prediction

3. design an experiment

4. conduct the experiment

5. analyze the data

6. communicate findings

Locard’s Principle of Exchange

when a person comes in contact with an object or another person, a cross-transfer of physical material can occur

hypothesizes that it is impossible for a criminal to act without leaving traces

Trace Evidence

small but measurable amount of physical or biological material found at a crime scenes

Class Evidence

narrows an identity to a group of persons or things

Individual Evidence

narrows an identity to a single person or thing

Parts of Hair

Shaft

• contains keratin

• keratin is a protein that provides hair its strength and shape

Follicle

• club shaped

• contains DNA

Sebaceous Gland

provides oil

Parts of the Shaft

Three Layers

• Medulla: inner layer

• Cortex: middle layer; contains melanin

• Cuticle: outer layer

Medulla Patterns

Continuous:

• one unbroken line or color

Interrupted/Intermittent:

• pigmented line broken at regular intervals

Fragmented/Segmented:

• pigmented line unevenly spaced

Solid:

• pigmented area filling both the medulla and the cortex

None:

• no separate pigmentation in the medulla

Hair Evidence Analysis

with follicle - nuclear DNA —> individual evidence

without follicle - microscopic pattern or mtDNA —> class evidence

can provide the persons’s characteristics (race, sex, age)

Fingerprints

an impression left on any surface that consists of patterns made by the ridges on a finger

imprint consists of excretions;

• water

• oils

• salt

• dirt

a piece of individual evidence

formed beginning at the 10th week of gestation (time since conception)

identical twins have different fingerprints

fingerprints are protected by the outer layer of epidermis (outermost layer of skin)

fingerprints cannot be altered or destroyed

Fingerprint Patterns

Loop - 65%

Whorl - 30%

Arch - 5%

Minutiae

def: very tiny fingerprint ridge details that can help compare/contrast a set of fingerprints

12-15 minutiae should match

1. ridge ending (including broken ridge)

2. fork (bifurcation)

3. island ridge (short ridge)

4. dot (very short ridge)

5. bridge

6. spur (hook)

7. eye (enclosure)

8. double bifurcation

9. delta

10. triple fork (trifurcation)

Digital Footprint

an online form of evidence that can be used to examine an individual’s activities across multiple platforms, such as social media apps

can determine where and when an individual has been

Function of Blood

carries oxygen and nutrients to all parts of the body

carries carbon dioxide and other waste products back to the lungs, kidneys, and liver for disposal

fights against infections and helps heal wounds

Facts About Blood

adult has about 5 L of blood in their body

7-8% of a person’s body weight

1 billion red blood cells in 2-3 drops of blood

for every 600 red blood cells;

• 40 platelets

• 1 white cell

Components of Blood

1. red blood cells

2. white blood cells

3. platelets

4. plasma

Red Blood Cells

scientific name: erythrocytes

most abundant

contains hemoglobin (iron), which carries oxygen to our cells

White Blood Cells

scientific name: leukocytes

fight infections

• white blood cells increase in response

Platelets

scientific name: thrombocytes

responsible for clotting

• don’t want too little or too much clotting

Plasma

yellowish liquid portion

contains H₂O, electrolytes, nutrients, hormones, and antibodies

carries nutrients across the body

Presumptive Testing

the initial testing that suggests a sample may be blood

usually performed at the scene

identifies blood on its properties, such as hemoglobin

Leucocrystal Violet (LCV)

type of presumptive testing

turns a violet color when it reacts with hemoglobin

used on porous/permeable surfaces

not the best test to use in lab environments

Luminol

type of presumptive testing

glows bright blue in the dark when it comes in contact with blood (presumably)

reacts with other substances, not just blood

not the best test to use in the lab

Kastle-Meyer Test

most common type of presumptive testing

uses phenolphthalein

• reacts with the iron carried by hemoglobin

can be used in the lab

positive result = pink color

RSID Test

designed to identify glycophorin A

• a human-specific protein

• found on the surface of human erythrocytes

confirms if a sample is human blood

detects glycophorin A by using two monoclonal antibodies that are formatted in a lateral flow

test cassettes show a different amount of red lines

ABO Blood Type Testing

determines if the sample is type A, B, AB, or O blood

identifies ABO antigens on erythrocytes and corresponding antibodies in serum

results are displayed through clumps or a smooth mixture

Positive Control

a sample/group that the researcher expects to have a positive result

shows that the experimental setup was capable of producing results

Negative Control

a sample/group that is expected to produce a negative outcome

negative control groups help identify confounding variables

Antigen

anything that stimulates an immune response

the absence and/or presence of these structures on erythrocytes’ surfaces can determine what type of blood a person has

Antibodies

a protein produced by B cells (type of white blood cells) that works to impair pathogens

Agglutination

the clumping of particles

can occur when blood antigens and their corresponding opposite antibodies are exposed to each other

Blood Typing

4 Types;

• A

• B

• AB (universal recipient)

• O (universal donor)

A and B are codominant

O is recessive

determined by attached protein called antigens

• A = antigen A

• B = antigen B

• AB = both antigen A and B

• O = neither

plasma contains antibodies based on type

• A = anti-B bodies

• B = anti-A bodies

• AB = none

• O = anti-A, anti-B

blood type must match for transfusion

Transfers

type of blood spatter that is produced when a blood source comes into contact with a surface

• smudges

• smears

• hand prints

Spatters

type of blood spatter that is produced when a source of liquid blood travels through the air before landing on a target surface

Falling Droplets

type of blood spatter that is produced when a droplet of blood is dropped directly from above and strikes a horizontal surface at 90°

diameter of the circular stains can be used to predict the height the droplets fell from

Force and Direction

type of blood spatter that is produced when an external force was applied that provided horizontal velocity, speed in a given direction, to the droplet

the more elongated the droplet, the faster they were moving

the long tail of each droplet indicates the direction it was moving when it struck the surface

Radial Spatter

type of blood spatter that is produced when there was an impact (the larger pool), which sent blood droplets traveling away from the impact at high speed

the impact occurred with significant force.

Cells

basic unit of life

all organisms are made u of cells

all existing cells are produced by other living cells

DNA (deoxyribose nucleic acid)

stores, copies, and transmits genetic information

double helix

composed of nucleotides

Nucleotides

contains;

• deoxyribose - 5 Carbon sugar

• phosphate group

• nitrogenous base

4 Different Types of Nitrogenous Bases

1. adenine (A)

2. guanine (G)

3. cytosine (C)

4. thymine (T)

Chargaff’s Rule

noticed that the relative proportions of DNA bases were similar between A and T, G and C

• concluded that A=T, C=G

Gene

a specific sequence of DNA that codes for a specific trait

Genome

a complete set of genes in an organism

Chromosomes

tightly coiled DNA that is found in the nuclei of cells

healthy humans have 46 chromosomes in somatic cells (23 in sex cells)

Eukaryotic Cells

cells that have membrane-bound organelles

Prokaryotic Cells

cells that lack membrane-bound organelles

unicellular organisms are prokaryotic

Organelles

tiny structures that perform a function in a cell

examples;

• nucleus

• ribosomes

• cell membrane

• mitochondria

Why Might DNA Be Analyzed

1. Body ID

2. Genetic Testing - paternity, maternity, ancestry, medical reasons

3. Forensic Evidence

Steps in DNA Analysis

1. Extraction

2. Polymerase Chain Reaction (PCR)

3. Restriction Digestion

4. Gel Electrophoresis

DNA Extraction

get DNA out of cells

must lyse the cell

• break down the cell’s membrane

not usually a large sample

Polymerase Chain Reaction (PCR)

produce millions of copies of a specific DNA sequence

make enough to analyze

steps (repeated 30-40 times);

• denaturation - strands separate

• annealing - primers attach to a sequence’s ends

• extension - build new strands

Restriction Digestion

restriction enzymes cut DNA at specific sites (recognition sites)

• over 200

• some cut straight through - blunt ends

• some cut at angles - sticky ends

• produce RFLP’s (restriction fragment length polymorphism)

Restriction Enzymes

a specialized protein that recognizes specific nucleotide sequences and cuts DNA at these sequences called restriction sites

named after the bacteria from which they were discovered and typically follow a standard naming scheme: 

• Bacterial Source

• Strain (or genetic variant)

• Order of Discovery

Gel Electrophoresis

used to separate and compare DNA fragments

negatively charged DNA moves toward positive pole

gel filters DNA fragments by size

larger pieces move more slowly through gel than smaller ones

Sources of DNA

• bone

• hair

• preserved body parts

• clothing and fibers

• saliva/body fluids

DNA Ladder

the baseline for DNA analysis

composed of known sizes of DNA

Accuracy

how close a measurement is to the true or accepted value

Precision

the degree to which repeated measurements show the same result