Forensics Second Midterm

Toxicology

the identification and quantification of toxins and illicit or prescription medications present in a person’s blood or bodily tissues

Although dealing with blood and bodily tissues, as well as the

physiological and psychological effects on humans, the work of

toxicology is primarily _________

Chemistry

Some cases involve deliberate poisoning, but most cases seen in a

crime lab will be drug overdoses, drug-facilitated sexual assaults, and

impaired driving cases.

Postmortem versus antemortem Toxicology

• involves testing blood, other bodily fluids, as

  well as tissue samples obtained from autopsy

Most crime lab cases are antemortem toxicology using blood (most

common*), urine, and oral fluid (saliva). Of which, impaired driving

cases represent, by far, the greatest number of cases.

Postmortem Toxicology

• Various fluids and tissues may be collected during autopsy.

Blood is usually collected from a femoral vein (in the leg) because

drugs can diffuse from organs like the liver back into blood after

death and central blood (such as from the heart) can contain higher

concentrations because they’re nearer the organ sources.

• Peripheral blood generally better reflects antemortem concentrations.

Ocular fluid (from the eyeball) is also frequently sampled. For

example, alcohol freely exchanges during life but stops immediately at

death so ocular fluid can be a good indicator of alcohol level at the

time of death*.

Postmortem Tissue Toxicology

• tissue samples taken from autopsy to test for drugs and toxins

Lab process the same as for fluid samples except the tissues need to be homogenized for extraction of analytes.

• Tissue samples can be especially important in cases of suspected

toxins as different substances accumulate to different degrees in

different organs.

Antemortem Toxicology

• involves testing fluid samples from living subjects.

• The most common is blood, followed by urine*, followed by oral fluid

(saliva)**.

• Occasionally, hair is tested because drugs and toxins can accumulate

in the keratin in hair and testing hair samples at various lengths can

provide a time profile of exposure.

Reasons for Antemortem Testing

• impaired driving is the most common reason for toxicological testing of the living.

• Blood and urine testing in sexual assaults is routine.

What is Biometrics?

identification of individuals using some anatomical characteristic

• friction ridge patterns (fingerprints)

• iris patterns

• retinal patterns

• all involve pattern comparison between evidence and reference pattern

• if the same = infer evidence comes from source

When did forensics start using fingerprints?

the 1800s

• Alphonse Bertillon introduced system of anthropometry for identification of criminals

• involved many precise measurements of physical features → identifying individuals

• was not practical for crime scenes

• Two people with identical measures were found (may have been twins)

• Replaced by fingerprints at the end of the 1800s.

Friction Ridge Impressions

• found on fingers, palms, toes, soles of feet, etc.

• ridges provide friction to help grip and for texture detection

• patterns of pores can be used for identification

Adermatoglyphia

absence of friction ridges/ fingerprints (rare)

We do not have definitively proof that_________ exist but exact duplicates have not be found

Duplicate Fingerprints

Fingerprint Class Characteristics: What are the three categories of ridge patterns?

• loops

• arches

• whorls

what percent of people have loops?

60-65%

What percent of people have arches?

about 5%

What percent of people have whorls?

30-35%

Fingerprint Sub-Class Characteristics

• Loops, whorls and arches can be sub-categorized to further refine

  searches.

  • Loops can be radial or ulnar

  • Arches can be plain or tented

  • Whorls can be plain, central pocket loops, double loops, or “accidental.”

Class characteristics have what?

Sub-class characteristics

Fingerprint analysts now generally use a method called ______

• ACE-V

• Developed by Royal Canadian Mounted Police

• Four Step process

What is the four step process of ACE-V?

1. Analyze- assess the quality and suitability of the impression

2. Compare- compare the unknown with a known for similarity/difference

3. Evaluate- determine sufficiency for inclusion, exclusion, or inconclusive

4. Verify- independent (preferably blind) review by second analyst.

What is the critical step in ACE-V?

verification

Iris recognition and Forensic Science

From computerized iris recognition, mathematical and statistical

concepts for pattern comparisons like fingerprint analysis have been

developed.

• Computerized iris and retina pattern analysis have shown how math

  and statistics can be used in all forensic pattern analysis.

• Important mathematical concepts describing uniqueness have been

  borrowed from thermodynamics (chemistry and physics).

• Iris scanning has been added as a component in the FBI’s Next

  Generation Identification system.

Degrees of freedom

DF= number of ways a system (pattern) can vary

• The more DF, the more possibilities for randomness. The more

  randomness, the more opportunities for uniqueness (individualization)

AFIS (Automated Fingerprint Identification System)

• a biometric technology used for scanning, storing, and analyzing digital fingerprint data against a computerized database.

• enables law enforcement to quickly compare latent prints from crime scenes against millions of known records to identify suspects and confirm identities.

• more advanced system has replaced it (from 92% to 99.6% accuracy)

• palms are searchable now

What is a tool mark?

a mark made by one object (the tool) coming into contact with another (the substrate) with sufficient force to make a permanent mark int he substrate

• can happen through plastic deformation → pressure from tool causes material in the substrate to move, imprinting a new shape to the substrate

• also caused by scoring

plastic deformation

the permanent, irreversible change in a material's shape or size that occurs when an applied load exceeds its elastic limit

scoring

tool mark analysis refers to a type of striated mark—a scratch or abrasion produced when a tool is placed against a surface and moved parallel to it under pressure

For tool mark to be of forensic value, they must:

1. Have some degree of uniqueness

2. be permanent, or at least sufficiently stable to analyze

3. be reproducible and reliably transferrable to other substrates

• The (often unknown) degree of uniqueness is a key source of criticism

  of tool mark analysis

Class characteristics

Features unique to a group, but not specific sources

Individual characteristics

Have a very high probability of unique association with an individual

The _____ only refers to the projectile. The ENTIRE “bullet” is called a _________

Bullet

cartridge

• powder stored in cartridge casing, bottom is primer while tip is bullet

Barrel

the tube through which the bullet passes to accelerate and be guided toward the target

Muzzle

the end of the barrel from which the fired bullet emerges

Breech

the rear part of the barrel where the bullet enters.

Chamber

The part of the firearm that holds the cartridge at the entry end of the barrel during firing. The chamber may or may not be fixed to the barrel. If so, the breech refers to the opening into which

the cartridge assembly is loaded.

Firing pin

a narrow pin-like component that strikes the primer to set off the explosive and ignite the propellant.

Hammer

a device that is held back under spring tension that is released by the pull of the trigger.

• hammer travels forward quickly and hits the firing pin causing it to strike the primer.

• Some hammers have an integral firing pin and strike the primer directly.

Striker

a spring-loaded firing pin that is directly released by the trigger instead of being struck by a hammer.

Trigger

an external piece that, when pulled rearward, releases the

hammer or the striker.

Rifling

The inside of the barrel has groves and ridges all around in a spiral. This allows the bullet to spin as it passes through the barrel. It allows it to be more stable and more accurate

Most modern firearms, other than shotguns but including most handguns have______

rifled barrels

• the high point in the barrel (called lands) create grooves in the fired bullet and the groves in the barrel create lands on the fired bullet

• manufacturing creates tool marks in the barrel which in turn, creates tool marks on the fired bullet

Comparing _____ is like comparing barcodes

Striae

• take straie, line them up, see if there the same

The number of lands and grooves in a barrel (and on a bullet) and the direction of their spiral twist (left or right) are both what? This allows forensic scientists to narrow down the potential type of fire arm.

Class characteristics

Because the manufcaturing tools change slightly with each use, the tools mark their impact to a barrel can be highly ________

Individualized

• even bullets fired through sequentially manufactured barrels can be identified,

• fired bullets can confidently be linked to a specific firearm

Cartridge Case Marks

Marks left on a fired bullet from the barrel

• marks left on cartridge case during loading, firing, and extraction from chamber as well as ejection from firearm

The most common area for examination is the _____ since features of the end of the firing pun can be impressed into the soft metal of the primer.

primer

Drag Marks

• distinct, striated tool marks found on the primer or base of a fired cartridge case.

• can be individualizing and indicates firearm mechanism

Shear Marks

• caused by the primer material being forced backward into the firing pin aperture and then sliced.

Drag and Shear marks are used to do what?

Identify a firearm

Extractor Marks

can be left on the rim of the cartridge case from the hook that pulls the fired case from the chamber.

Ejector Marks

can be left on the edge of the case head from the cartridge case striking the ejector.

Chamber Marks

can be left on the sides of the cartridge case from the firing process.

Magazine Marks

can be left on the sides of the cartridge case from being loaded into, or stripped from, the magazine

What are drugs?

anything that has a physiological or psychological effect

Many drugs occur in what?

Nature

• alcohol, caffeine, etc.

• many drugs are plant materials consumed for for their active ingredients (shrooms, THC)

• some drugs are federally illegel to possess or use

Cannabis is ________ but ______ in many states

• illegal federally; legal

• complicated because its the same plant as hemp (legal) difference is levels of THC

By definition, marijuana is cannabis with more than _____ THC

0.3%

Depressants

Slow CNS functions; calming, disinhibitory

Stimulants

excite CNS functions; energizing, but often euphoria

Narcotics

Deaden sensation (anesthesia), sleep-inducing, can be euphoric

Hallucinogens

alter thoguhts, mood, or perceptions; may be dissociative (outside of the body)

Marijuana is sometimes classified as a _____ due to its mood and thought alteration but also has a calming effect

hallucinogem

Drugs are often categorized by their ____

effect

Drug scheduling

categories of drug based on their medical use and abuse potential, not on effects

The Controlled Substances Act of 1970 created what?

Drug scheduling scale (5 categories)

Schedule 1

High potential for abuse, no accepted medical use

Schedule 2

High potential for abuse, restricted medical use

Schedule 3

Less potential for abuse, common medical use

Schedule 4

Low potential for abuse, common medical use

Schedule 5

Less potential for abuse than schedule four drugs, harmless

Presumptive Tests

simple and quick methods for testing for the presence of drugs in the fields

-cross reactivity or sensitivity changes in conditions

ex. color tests for solid drugs and preliminary breath testers for alcohol

presumptive tests not always accurate → wrongful conviction

Mass Spectrometry (MS)

• used for confirming drug tests (like immunoassay)

• ionizes molecules in a vacuum and measures the mass of the ions. The ionized molecules fragment in consistent ways, forming a fragmentation pattern that is unique to the substance

• sample broken into mini charged particle → ions sorted based on their mass-to-charge ratio → each drug creates a unique fingerprint pattern = compares the sample fingerprints to known drug patterns

Infrared Spectrometry (IR)

• most molecules absorb infrared light at specific wavelengths depending on the molecular structure. When plotted, the wavelengths and intensities of the absorptions form a unique pattern.

• Ir shines infrared light through a sample → different chemical bonds absorb specific wavelengths of ight → creates an IR spectrum (kind of molecular fingerprint) = identifies function groups (alcohols, amines, etc.)

Nuclear Magnetic Resonance (NMR)

• forms unique patterns from nuclei in the molecule absorbing radio frequencies when under a magnetic field.

• places a sample in a strong magnetic field → Certain atoms (especially hydrogen) respond to radio waves → the signals reveal how atoms are arranged in the molecule—basically the full structure = It gives very detailed structural information

Chromatography

Used to provide seperation into individual chemical components

• When a sample has a mixture of substances, the signals overlap, so you can’t tell what’s what. So first, the mixture is separated into individual parts.

• might separate based on properties (how they dissolve/react)

• chromatography then seperates mixture → It uses a moving fluid (gas or liquid) to carry chemicals through a system → Different substances move at different speeds, so they come out at different times (retention time) = helps identify what substance it is

Why is retention time important to chromatography?

if the solvent and other conditions are constant, the retention time shown by the chromatography demonstrates what drug it is

Category A is the most what?

Discriminating

• definitively identifies a specific drug

• they give very detailed “fingerprints” of a substance (MS, NMR, FTIR)

Category B

• give supporting information but not full confirmation on their own.

• They help narrow down possibilities of what drug it might be

• Chromatography, etc.

Category C is the what?

Least discriminating

• basic tests that only give general clues.

• They can suggest a class of drug but not a specific one.

• color tests, spot tests, etc.

Toxicology

• uses a lot of same equipment/methods for seized drug analysis

• difference is toxicology looks for drugs in blood, urine, bodily tissues, etc

• Concentrations are important for toxicology (weight per unit of volume)

• Separation/extraction of the substances of interest from the blood or tissue is a critical step. Alcohol can be separated and analyzed relatively easily because it is volatile. Other drugs are more complicated

Toxicology uses _________ - Very often immunoassay

Presumptive testing

Measurement Uncertainty

• Any measurement has uncertainty as to whether the measured value is the true value of measurand

• Science uses standardized methods to estimate measurement uncertainty (MU). Reporting MU is now standard in forensic practice.

Each method has inherent uncertainty. Combining methods adds uncertainty. For example, measuring drug weights can have very loe uncertainty. Measuring alcohol in blood or breath can have a MU of about ± 5%. Drug concentrations in blood can be about ± 20%.

Measurand

The specific thing you are trying to measure.

Serology

study of serums

• stains at crimes can be identified using serology

• Kastle-Meyer/Hemastix may presumptively identify a stain as blood

• Luminol → blood stain visibility using fluorescence

• Identifying stains helps determine areas for DNA analysis

Semen stains may not be visible under normal light but may be using

ultraviolet light

Acid Phosphatase

test may presumptively identify a stain as semen

• semen may/may not have visible spermatozoa under a microscope

P30 aka Prostate specific antigen (PSA)

used to confidently identify a stain as semen

Forensic DNA Profiling…

• does not involve sequencing the entire genome.

Foresnic DNA does not involve what?

sequencing the entire genome

STRS

Forensic DNA profiling uses specific sites on chromosomes that vary significantly between individuals. These sites are known as micro satellites or short tandem repeats

• short DNA sequences that re repeated over and over in a row at certain spots in a genome

Heterozygous

A person with two different alleles (brown, blue)

Allele

the variations of the different versions of genes

example:

one allele = brown eyes

another allele = blue eyes

you inherent one allele from your mom and one from you dad

• An allele can mean a different number of repeats at a specific DNA location

Homozygoous

A person with two of the same alleles (brown, brown)

There are about ____ standard STR sites used in profiling

25

• STRs from small amounts of DNA can be quickly amplified millions of

  times using polymerase chain reaction (PCR).

• Population frequencies are known for each STR allele so probabilities

  of a specific combination can be determined.

Random Match Probability

• the chance that a random, unrelated person would have the same DNA profile as the one found in a sample.

• After analyzing DNA, scientists get a profile → what are the odds a random person chosen has the same DNA profile? →Only 1 out of 1,000,000 unrelated people would be expected to match that DNA profile.

• Shows how strong the DNA evidence is

• The smaller the probability, the more unique and reliable the match

Electropherograms

a plot of the STR alleles

• PCR process generates mixture of all STR alleles present

mixture is separated using gel electrophoresis which separates each allele by size

Mitochondiral (Mt) DNA

• the small amount of DNA found in the mitochondria, not the nucleus,

• Mitochondria are only inherited from the mother

• MT can be used to trace maternal lineage

Y STRs

• Y chromosomes are only present in genetic males. They are inherited

  exclusively from the biological father.

• can identify male lineage.

Genetic Phenotyping

• the process of using a person’s DNA to predict their physical traits (appearance or biological characteristics).

• Full DNA sequencing is now being used for predicting the source’s

  appearance using genetic phenotyping.

Genetic genealogy

• the use of DNA testing combined with family tree research to find relatives or trace ancestry.

single nucleotide polymorphism (SNP) sequencing can be used in genetic genealogy to identify unknown sources.