FORENSIC SCIENCE Notes

FORENSIC SCIENCE Notes
Chapter 1: Introduction
Sir Bernard Spilsbury is the 1st forensic science celebrity.

A legal system does the following process,
1. Collect evidence from experts, witnesses and police
2. Prosecution and defense lawyers present cases and arguments
3. Judge and Jury (abolished in some countries including Singapore) decides outcome
*Innocent until proven guilty beyond reasonable doubt.

Limits of Forensic Science
Actus Reus: A guilty action
Mens Rea: A guilty mind or intention
(The act does not make a person guilty unless the mind is also guilty)

What is ‘forensics’?
An application of Science to Law, Science to Criminal Justice
The analysis of physical, chemical and biological evidence
Forensic Medicine deals with crimes involving a human body (Murder, rape, assault)

Forensic science enables us to reconstruct the past sequence of events.
Forensic science can link a suspect to a crime scene. Examples of forensic evidences are:
Fibres (clothes, carpet)
Hair
Blood
Fingerprints
Shoe print
Paint

Forensic evidence can distinguish between murder and suicide.

Locard Exchange Principle by Prof. Edmond Locard
“Wherever he steps, whatever he touches, whatever he leaves, even unconsciously, will serve as a silent witness against him. Not only his fingerprints or footprints, but his hair, the fibers from his clothes, the glass he breaks, the tool mark he leaves, the paint he scratches, the blood or semen he deposits or collects. All of these and more, bear mute witness against him. This is evidence that does not forget. It is not confused by the excitement of the moment. It is not absent because human witnesses are. It is factual evidence. Physical evidence cannot be wrong, it cannot perjure itself, it cannot be wholly absent. Only human failure to find it, study and understand it, can diminish its value.”
Every Contact leaves a Trace

Case Study: Burglar severed a finger on razor wire while breaking into a builder’s yard was caught by police when he went to hospital for treatment.
Earliest forensics lab in US is in Austria, USA in LAPD.
Singapore’s forensic lab is set up in 1960 by Prof Chao Tzee Cheng, now part of HSA.

In a Forensic Science Lab, you can find:
1. Physical Science Unit
a. Identification and comparison of evidence
b. Chemical tests
c. Spectroscopy
d. Microscopy
e. Drugs, glass, paint, explosives, soil…

2. Biology Unit
a. Hair
b. Plants
3. DNA Lab
a. DNA analysis

4. Firearms Unit
a. Guns
b. Bullets
c. Cartridge cases
d. Firearm damage

5. Documents Unit
a. Handwriting
b. Printing
c. Paper
d. Ink

6. Photography Unit
a. Record of evidence
b. Presentation

Toxicology – drugs and poisons in body fluids and organs

Latent Fingerprints – using chemical means to making them visible

Polygraph – or lie detector

Voiceprint – analysis of voices

Psychiatric Profiling – What can we tell about the criminal from the way they commit the crime

Computer Forensics and Electronic Forensics – What can be learnt from deleted data? How can other electronic trails be followed?

Forensic Engineering – Examine the engineering aspects of a building or object

Forensic Entomology – Using insects to provide information

Forensic Geology – Soil Analysis on mineral content and chemistry. Soil in different countries have individualistic composition. This composition helps to narrow down to a region of the world.

Forensic Anthropology – Examination of skeletal remains

Facial Reconstrution – If you have the skull, can you tell what the face looks like?

Forensic Odontology – Using teeth to provide information such as identification of victims remains or criminal

Identification:
Physical objects
Biological properties
Chemical properties/constituents
We collect as many evidence as we can on scene.
These evidences have class characteristics that can put an object in a certain class or group like brand of shoe, type of fibre or type of bullet.

Individualization:
Narrowing the class to one,
Attaining more information from evidences from a crime scene.
Physical objects: Manufacturer, serial number, fingerprints
Chemicals: Trace elements and impurities
Biological samples: Blood type and DNA analysis

Then we do comparison and associate the evidence to the crime scene and the criminal.
After which, reconstruction to understand the sequence of past events and Re-enactment

Chapter 2: Spectroscopy and the Structure of Atoms
Elements are the basic materials consisting of 93 natural basics and many more artificial ones.
Elements can neither be created nor destroyed.

Paper Cellulose consists of C, H, O  Carbon Dioxide CO2 and Water H2O

Human Body consists of C, H, O, N, P, S, Ca, Na, K, Fe… CO2, H2O, N oxides, P oxides, S oxides, Ca oxides or hydroxides… Teeth contains Au or Hg  Au or Hg oxides

Analysis: Which elements are present?
E.g. Suspected lead or mercury poisoning but are these metals present in the body regardless of their chemical form? Toxicology.
E.g. FUN analysis. How much of these elements were present in the Piltdown bones? Time of Death.

What is it made of? How can we identify the elements present in an object?
Bulk composition (what is it mostly made of?)e.g. bullets are mostly lead.
Trace impurities (what is a small part of it made of?) e.g. bullets have silver and antimony

Chemical tests can be done to identify these elements and chemical tests have the following characteristics:
Large amounts of sample is needed
Destructive
Subjected to interference
Fast process
Easy to do
Simple equipment

White light consists of all colours. In the early 19th century, black bands observed in the solar spectrum. Different spectroscopic techniques use different frequencies of light. The different frequencies of light interact differently with the molecules.

Structure of Atom: Tiny, dense, positively charged core called nucleus where nearly all mass is concentrated with electrons circulating at some distance. Founded by Ernest Rutherford.

Niels Bohr found that electrons are restricted to specific energy levels, therefore atoms don’t destroy themselves due to electrostatic attraction.

Electrons can jump to higher energy levels by absorbing energy.
Electrons can release energy when they drop to a lower level.
The frequency of the electromagnetic radiaton emitted or absorbed is proportional to ΔE
De Broglie equation: E = hv (Constant x frequency of electrons)

Absorption Spectroscopy is when electron jump to higher energy levels, energy is absorbed. A drop in graph for short interval of time.
Emission Spectroscopy is when electron drops to lower energy levels, energy is given out. A sharp spike in graph.

Flame tests for metals: if a metal salt is introduced to a flame, a characteristic colour is produced.
Energy of the flame excites electrons in the atoms and light is emitted as the atoms drop back to ground state.
Sodium: Orange
Barium & Copper: Green
Calcium & Lithium: Red
Potassium: Lilac
Atomic Absorption Spectrometer (AAS):
Advantages:
Fast
Specific
Sensitive
Small sample size
Disadvantages:
Destructive
Element by element

Neutron Activation Analysis (*NAA)
Non-destructive but needs a nuclear reactor
Changes the nature of element
Each emitted gamma ray is at diff. energy level.

Microscopy
Scanning Electron Microscope – Energy Dispersive X-ray fluorescence (SEM-EDX)*
Non-destructive analysis looking at core electrons
Use the electron beam of the microscope to eject core electrons
Ejecting a core electron creates a vacancy.
When a higher energy electron drops to fill vacancy, a characteristic X-ray is emitted

CASE STUDY: Napolean.
Analysis of hair samples by Neutron Activation Analysis shows arsenic. Paint used for one of Napolean’s wallpaper is Scheele’s Green which consists of copper arsenite. SEM-EDX shows presence of arsenic. When copper arsenite reacts with mold, arsenic gas is produced.

CASE STUDY: Kennedy Assassination 22nd Nov 1963
Analysis of bullets fragments by Neutron Activation Analysis (NAA) shows the content of Antimony and Silver.

You are What You Eat!
Bones consists of calcium phosphate in a protein matrix.
Calcium is derived from the diet..
Other metals may also be incorporated if they are present in diet.
Relative abundance of trace elements in bone can indicate geographical origin: Stronium, copper and lead.

Chapter 3: Time of Death
Algor Mortis:
After death, muscles relax, body is limp and starts to cool down. The rate at which body temperature cools depends on size of body, location, clothing, weather.
Different parts of the body cools at different rates. E.g. Brain cools faster than liver.
General rule is -1 to 1.5degrees Fahrenheit
However, note that the body may start to warm up after 2 days due to start of putrefaction

Rigor Mortis: Lactic acid in the muscles causes tension up to 36 hours after death E.g. Jaws (2hrs), arms (4-6hrs), legs(8-10hrs), whole body (10-12hrs)

Livor Mortis (Colour of the body):
Also known as Postmortem lividity: the black and blue discoloration of the skin of a cadaver, resulting from an accumulation of deoxygenated blood in subcutaneous vessels.
Hypostasis: poor or stagnant circulation in a dependent part of the body or an organ.
Settling of red blood cells due to gravity (post mortem lividity, hypostasis 0-12hours)
Discolouration in lower parts. Parts on the ground not affected due to compression of capillaries (contact flattening)
*Has the body been moved? If a body has been moved, the colouration of the body may not give the correct approximation of the time of death.
*Take note that CO poisoning has similar symptoms as Livor Mortis, CO poisoning results in cherry pink colouration due to the carbon monoxide-haemoglobin complex

Physiological Changes in the body after Death.
The average core temperature of a body is 9.6degree Fahrenheit. Postmortem interval = 99.6/1.5 (general rule).

Other indicators that can estimate the time of death are:
K+ levels in ocular fluid (vitreous humor) which increase after death
Stomach and intestine contents (time of last meal). A stomach empties its contents in about 2 hours.
Look at other objects such as watches or mobile phone records and CCTV.

Putrefaction
This is the process when your micro-organisms start to eat you after death. This produces gases and characteristic smells. The rate of putrefaction depends heavily on local factors such as temperature and also drug use.

Forensic Entomology (Using insects)
Insects can arrive and lay eggs as early as 20mins after death.
In order to estimate the time of death, the species, life cycle, local conditions of that particular insect must be known. Live maggots are collected from the corpse and rear until adulthood. After which, back calculate age and determine species.

Skeletal Remains
A forensic pathologist or anthropologist will use osteology, the study of bones, to find out as much as possible about the identity of a skeleton or collection of bones. Sometimes they rely on skeletal radiology, the study of bones through x rays or fluorescence (light-emission) to help make the identification.
No fluorescence indicates that the skeletal remains is 100 years old or more.

FUN analysis As time passes, the organic components of bone (mostly fats and proteins) are lost primarily through bacterial action. Since these components contain nitrogen, there is a progressive loss of that element. At the same time, percolating ground water deposits trace amounts of fluorine and other elements, such as uranium, into the bone. Bone nitrogen content decreases with age (proteins breakdown). Bone fluoride and uranium increases with age. Fresh bones should contain 4% of nitrogen and 0% fluoride and uranium.
Therefore, FUN analysis is useful for comparing samples from the same burial grounds/sites.

Carbon-14 Dating
The natural amount of 14C, a radioactive isotope formed in atmosphere by cosmic rays, is constant and living things have this proportion of 14C. Radioactive atoms decay at a preditable rate and only half of the atoms will have decayed in 5568years. Hence measuring the amount of 14C allows estimation of time of death through back calculation. This method is not accurate for <400years because amount of decay is too small. Moss (vegetation) accelerates the decay of 14C.

Algor mortis, Rigor mortis, Livor mortis, state of putrefaction, entomology, FUN analysis, fluorescence, 14C dating are all techniques to estimate time of death but they are subjected to errors.

Analysis of Compounds
Different compounds move at different speeds through an absorbent (stationary phase). Components can be detected as they get to the end. Movement is due to the flow of a liquid or gas (mobile phase).

Thin Layer Chromatography (TLC)
Coloured compounds are visible to the eye while others can be made visible through chemical staining or UV light. TLC is a presumptive test, it is unable to distinguish all the different compounds in the sample and only provides 2 answers: NO or MAYBE.

Gas Chromatography (GC)
GC can only be used if the unknown sample passes TLC. GC depends on the rate of which the compound moves at different temperatures. GC is still not accurate enough.

High Performance Liquid Chromatography (HPLC)
HPLC is similar to GC, but uses a liquid mobile phase. The graph result of HPLC has very sharp and narrow peaks which are highly distinguishable to determine the different compounds in an unknown sample accurately.

HPLC vs. GC
For both methods:
Efficient, highly selective and widely applicable
Only a small amount of sample is needed
Non-destructive to the sample
Readily adapted to quantitative analysis
Has high resolution

Advantages of HPLC:
Can accommodate non-volatile and thermally unstable samples

Advantages of GC:
Simple and inexpensive equipment
Rapid process

How do we tell what compound is it?
By comparison of chromatography of authentic samples
By spectroscopy
By spectrometry

Infra-red Spectroscopy
Based on molecular vibrations (stretching and bending of chemical bonds)
Stretching frequency depends on masses involved and stiffness of the bond
The graph of infra-red spectroscopy has 2 parts, before 1500 wave number and after 1500 wave number
Before 1500-6000 wave number shows the characteristics of the class of compounds, but not of individual compound
After 1500 – 600 wave number shows Characteristic of individual compound like a molecular fingerprint

Mass Spectrometry
Measures the molecular weight of the sample.
1. Sample is introduced into a vacuum box
2. Sample is bombarded with electrons, leaving only positively-charged ions
3. Ions are accelerated by high voltages (100 – 10,000V), ions is deflected into magnetic field to detectors, measuring the mass of the molecule.
*Know how to calculate molecular weight
Some molecules will break up in the spectrometer known as Fragmentation.

Gas Chromatography – Mass Spectrometry (GC-MS)
Another hyphenated technique.
IN GS-MS, the MS acts as the detector.

Chapter 5: Blood: Forensic Serology

Blood Composition
Blood is about 8% of the body weight and contains:
Blood Plasma – The fluid portion of blood (55% by weight), mostly water, proteins, waste products of metabolism, nutrients on the way to the cells
Blood Cells – many different types (45% by weight)
Red blood cells (Erythrocytes) principally for oxygen transport
White blood cells (Lymphocytes, Phagocytes, etc.) responsible for the immune response
Platelets for blood clotting
Serum – the liquid that separates from blood when a clot is formed
Erythrocytes (Red Blood Cells)
Principle function is oxygen transport on Haemoglobin protein. Each protein has 4 oxygen molecules.
Large quantities of carbonic anhydrase catalyse the reaction of CO2 to HCO3 for the transport of CO2 in the blood.

Blood Typing
Surface of red blood cells contains proteins called Antigens.
There are 30 commonly occurring antigens with >100 rarer ones identified.
The most common antigens are A-B-O system of blood typing.

ABO Blood Types
Four basic blood types
Type A: A-Antigen on surface of red blood cells
Type B: B-Antigen on surface of red blood cells
Type AB: both A and B Antigens on surface of red blood cells
Type O: neither A or B antigens on surface of red blood cell

Antibodies
Constitutes about 20% of the blood plasma volume.
Class of proteins called “Immunoglobins”.
Produced by plasma cells as part of the immune response.
Bind to objects in the blood that they regconize as “alien”.

Serum Antibodies
The blood serum contains antibodies to the surface antigens: Anti-A and Anti-B.
The antigen-antibody interaction is highly specific. It is the basis of the immune response.

Agglutination
Mixing blood Type A and Type B allows the Anti-A antibodies (from type B) to mix with A antigens (from Type A) causing Agglutination.
Agglutination results in blood clotting.
This is why blood transfusion has to match the blood type.
Anti-A antibodies from Type B blood only regconizes A antigens from Type A blood causing agglutination.

Rhesus Antigens

http://www.nobelprize.org/educational/medicine/landsteiner/readmore.html

*Blood type cannot prove guilt because it is not individualised
*Blood type can establish innocence to eliminate suspect

Presumptive Tests for Blood
Based on the peroxidase properties of blood
Benzidine Colour Test
Kastle-Meyer Colour Test
Phenolphthalein
Luminol Test

Chemical basis of the Kastle-Meyer Test
Swab the sample
Add reduced Phenolphthalein to swab
Add H2O2 to the swab
If blood is present, the reaction will cause the blood to turn pink due to oxidation.

Luminol Test
Method is used at the crime scene
Reacts with iron found in blood
Sensitivity: 30 parts per million

Precipitin
An antibody in blood that combines with an antigen to form a solid that separates from the rest of the blood.
Tests based on anti-sera produced in rabbits or rats
Inject human blood into a rabbit and the rabbit produces antibodies to human blood
Human anti-sera are available commercially. Other animal anti-sera are available to eliminate pets blood at the crime scene.
Antigen and antibody are added to their respective wells
Antigen and antibody are being moved toward each other
Antigen and antibody have formed a visible precipitin line in the gel between the wells.

Can the pattern of blood spatter be used to reconstruct the events?
Blood spatter analysis can identify if the blood spatter is arterial spurting or blood dripping (depends on surface).
A falling blood drop is spherical and will give a circular mark on the floor if falling at 90°
If the blood drop hits the wall or floor at an angle, the width and length of the mark will be different. The angle can be calculated by comparing the width and length.
If we know the angle at which the blood drop hit the surface, we can project back. The point where the lines converge is the source of the blood spatter.

*Kastle-Meyer and Luminol tests for blood.
*Precipitin tests whether it is human blood.
*Blood typing tells whose blood is it but not individualised.
*Blood spatter analysis to find the source of blood spatter at crime scene.

Chapter 6: DNA
Human body contains about 60 trillion cells. Each cell contains your genetic material in its nucleus: 23 pairs of chromosomes, weighing 7pg (pico grams)
Out of the 23 pairs of chromosomes, 22 pairs are autosomal (non-sexual). There are 2 sex determining chromosomes male XY and female XX (Y is smaller and different shape).
Different size and shape, largest denoted 1 onwards.
Different chromosomes contain different genes.
Pairs of chromosomes are described as homologous as they have the same size and contain the same genetic structure. One is inherited from the mother and the other from father.
When chromosomes are stained with fluorescent dyes they develop distinctive patterns of bright and dark bands.

Chromosomes
Chromosomes are nuclear DNA packaged in specific structural units in nucleated cells.
Within each chromosome, the DNS is wound around small proteins called histones.

Genes
The DNA material in chromosomes is composed of ‘coding; and ‘non-coding’ regions. The coding regions are known as genes.
The number of genes in the genome varies, more complex organisms tend to have more genes.
Genes range from 1000 – 10,000 base pairs in size.
Non-protein coding regions of DNA (approx 95%) – junk DNA. (Not used for anything)
Only 5% is used for coding in human body.

The Human Genome
A genome is all the genetic material. It is the entire set of gereditary instructions for building, running and maintaining an organism, and passing life on to the next generation.
Genome is divided into chromosomes, chromosomes contain genes, and genes are made of DNA

What is DNA made of?
A sugar, a phosphate, a base = a nucleotide
DNA is a polymer of nucleotides
The sugar is 2-deoxyribose
There are 4 types of nucleotides with bases Adenine, Guanine, Cytosine, Thymine. (A,G,C,T).
DNA is made of the gour nucleotides in polymer chains and the phosphate links the sugars. DNA is one big polymer molecule.

What is a double helix?
DNA consists of two chains wound together, held in place by hydrogen bonds. The bases in DNA hydrogen bond to each other.
But pairing of A and T or C and G is favoured (complementary base pairing)
A and T pair is combined using 2 hydrogen bonds
C and G pair is combined using 3 hydrogen bonds

The Genetic Code
We can write the code using 4 letters A,T,C and G.
A group of three letters (3 nucleotides) codes for an amino acid in a protein. (-C-C-T-G-A-G-G-A-G-)
-C-C-T  Proline
-G-A-G  Glutamate
One amino acid can have multiple amino acid codes. That means to say Proline can be –C-C-T and also some other 3 letter codes.

DNA Fingerprinting
Restriction Fragment Length Polymorphism (RFLP)
Needs blood or semen sample about the size of a dollar coin.
Uses Junk DNA.
Polymerase Chain Reaction (PCR)
Allows a specific region of DNA to be repeatedly duplicated.
25-30 cycles of PCR will give 1,000,000 copies
Can analyse very small amounts: 36 cells such as saliva from cigarette ends, backs of stamps, barely visible blood stains.

Short Tandem Repeats (STR)
STRs are repeating lengths of base pairs (3-7) in blocks up to 400 in total.
Comes in pairs.
Used for paternity and maternity testing: The STRs of child must match both parents.
Your DNA: half from mother, half from father randomly. Therefore brothers and sisters have different DNA except identical twins.

Mitochondrial DNA (mtDNA)
A circular genome located in the mitochondria.
Has 16,569 bases and 37genes
Non-coding region known as ‘D-loop’ exhibits variation between unrelated individuals of about 1-3%
Higher copy number per cell and so more resistant to sample degradation than nuclear DNA mtDNA is inherited strictly from mother and not unique to an individual
Has faster mutation than nuclear DNA

*9 cells can be a trace

Chapter 7: Fibres and Polymers
Polymer is a long chain molecule made of many repeating units

Fibre Examination
1. Microscopic to determine type (e.g. wool, nylon)
2. Colour
3. Physical features such as shape
4. Width
5. Delustrant (chemicals added for shininess)
6. UV light: Different fibre has different colour under UV light
7. Spectroscopic analysis of fibre and chemical analysis of dye (identify origin of fabric)

Identification of Synthetic Polymers
Synthetic polymers fibres are melted or dissolved then made by passing through dye
The shape of opening is the shape of the fibre and can be used to identify origin and when fibre was manufactured.
Infra-Red spectrum by Microspectrophotometry
Colour – Analysis of dye by chromatography
Manufacturer – Shape of fibre
Cannot be individualised, but can be traced to one manufacturer, at one period of time.
A sample from criminal and a sample from victim’s clothes can be used for IR comparison and if both fingerprints of the fibres are the same, then criminal is identified.
Natural Polymers
Starch and Cellulose are polymers of glucose
Starch: Can be digested by us
Cellulose: Structural material for plants. Cannot be digested by us (Cotton)

Natural Polymers – Proteins
Structural Material:
Tissue
Cells,
Hair
Nails
Part of bone (with calcium phosphate)
Enzymes:Proteins that do all the body’s chemistry (highly specialised)
Antibodies: Binding to alien intruders (highly specialized)

Hair
Anagen phase: Growth phase, up to six years
Hair pulled out will contain DNA in the root.
Catagen phase: Transitional phase as growth slows and stops (2-3weeks)
Telogen phase: Root has shrivelled and hair can fall out (2-6months). Not enough DNA.
Hair consists of 3 layers:
1. Cuticle: scales, useful for species identification
2. Cortex: Contains pigment granules (Colour, size, distribution, density)
3. Medulla: Width and pattern is characteric of species
If hair is exposed to chemicals such as drugs and toxins, cut off hair near the scalp for analysis.
Length of hair can determine period before victim’s death as hair grows 1.25cm/month
Hair can then be cut into segments for analysis of levels of drug/toxins.

Natural Fibres (cotton, silk,wool) are hardest to individualise.

Chapter 8: Drugs
Natural
Used since ancient times
Semi-Synthetic
Modified natural compounds
Synthetic
Misuse of pharmaceutical results
Abuse of solvents

Active ingredient in samples can be detected by HPLC.
Plant samples can be compared by DNA.

Detection and Identification
Presumptive tests
Chemical colour change: Marquis test
Heroin – red purple
Amphetmines – orange brown
Scott test for cocaine
Cobalt thiocyanate turns blue

Quantitative Tests:
GC and HPLC
Spectroscopic identification
IR fingerprint region
Hyphenated methods:
GC-MS

Immunoassay
Identification of a drug in a body fluid (blood , urine)
Generate antibodies to drug
Binding of substrate to antibody triggers colour change
Highly sensitive.

Chapter 9: Toxicology
Corrosives
Acids and alkalis (e.g. Sulfuric acid)
Irritants
Lead, mercury, arsenic
In gut can cause nausea, diarrhoea
Can have other effects after absorption

Systemic Poisons
Attack biochemical systems
E.g. Cyanide (mitochondria), carbon monoxide (haemoglobin), strychnine (nervous system)

Carbon Monoxide (CO)
Prevents haemoglobin from transporting oxygen from lungs to cells

Carbon Dioxide (CO2)
Less toxic – danger of asphyxiation

Accidental Poisoning
Meadow saffron contains colchicines, looks like wild garlic
Potato fruits and rhubarb leaves contain oxalic acid.

Toxins
Natural substances from various species. Also attack biochemical systems
Biological toxins are botulism and anthrax.

POISON: All substance are poisons, there is none which is not a poison. The right dose differentiates a poison form a remedy.

Measurement of toxicity (LD50)
Amount to kill half of a given population of test animals.

Size – larger doses are for larger bodies
Age – Metabolism changes with age
State of health-especially condition of liver.
History-Build up of tolerance and loss of tolerance
Paradoxical reactions: Rare but known

What Paracelsus did not say
1. A poison must reach the target organ:
Absorption into body
2. Build up to target organ before excretion

Route of Adminstration
To be effective: Must reach target organ
Oral administration – absorbed through digestive tract
Intravenous – directly into blood stream, efficient
Inhalation – rapidly from lungs to blood
Through mucus membranes – often fast and efficient

Alcohol
Conviction of drink-driving
More than 35ug of alcohol per 100ml of breadth.
More than 80mg of alcohol per 100ml of blood.
Distribution of Alcohol
Absorbed by stomach (20%) and small intestine (80%)
Appears in blood in minutes: Complete in 30-60mins
Rate of absorption depends on kind of drink and stomach contents
Distributed via cardio-vascular system

Elimination of Alcohol
Ethanol  Liver, small intestine  Liver  Carbon Dioxide (95-98%)
2-5% absorbed by kidneys and lungs

Distribution of Alcohol
Uniformly throughout the body, except
-bones, fat, hair (low water content)
-Higher in arterial blood than veinous blood during absorption
Blood alcohol can be measured by GC
Measure breath alcohol
Post mortem – blood, urine, vitreous humor (Ocular fluid)

Henry’s Law states that for solutions at low concentrations the vapour pressure of the solute is proportional to its mole fraction. The amount of alcohol in blood is proportional to the amount of alcohol in breath.
35ug in 100ml of breath
80mg in 100ml of blood

Blood Alcohol Curve
Back calculate from time of test to time of incident

Inorganic Poisons
Elements may neither be created nor destroyed.
If you poison someone with arsenic, antimony, mercury, thallium, the element will still be detectable after death, after burial and even after cremation.

Thallium
Formerly widely available as rat poison.
Lethal dose 12mg/kg
Interferes with nervous system due to similarity with potassium.

Barium Meal
To take X-rays of digestive system.
Uses insoluble barium sulphate (BaSO4)
Cannot be absorped
Cannot reach the target organ

Sarin
Shuts down nervous system, nerve stimulation – twitching – convulsions – death.
Often starts with blindness due to effect on eye nerves and muscles.

Atropine
Antidote to Sarin, inhibits action of acetylcholine
Has been used in optometry

Chapter 10: Fingerprints
DNA can calculate statistically that no 2 people have same DNA (except identical twins)
Fingerprints: 100+ years of experience, no two people have same fingerprints including identical twins.
First Principle – No two fingers have the same prints including identical twins.
Second Principle – Fingerprints do not change during a lifetime (and remain after death for some time)
Third Principle – Patterns can be classified.

Latent Fingerprints – Requires chemical visualisation
Origin of Fingerprints – Secretions from the skin
Eccrine, Apocrine, Sebaceous glands, metal salts, amino acids, proteins, fats and water.

Dusting powder
Molybdenum Disuphide
Aluminium
Carbon black
According to background contrast.
Lift print on tape

Visualisation Reagents
Ninhydrin reacts with amino acids
Iodine spray
Silver Nitrate

Laser fluorescence
Alone or using a dye

Chapter 11L Firearms
Internal Ballistics
External Ballistics
Terminal Ballistics

Firing Pin: strikes end of cartridge, primer detonates and propellant explodes
Firing pin impression is characteristic
Rifling: Improved accuracy and stability

Striations
Characteristic scratch marks on the bullet created as it travels down the barrel
Fire another bullet from the gun and use comparison microscopy.

Gun Shot Residue (GSR)
-Residues from explosion of primer and charge
-Deposited near the discharged weapon:Hands and clothes of gunman clothes of tgarget depending on distance.
-Most GSR and GC go into wound. Gases exiting would characterios cross shape.

Griess Test
Nitrite (X NO2) residues from nitrate, nitrocellulose, nitro glycerine
Griess tests on hands may be positive due to fertilizer, urine, cosmetics, tabacoo.

Sodium Rhodizonate
Tests for lead, barim and antimony from primer
Colour changes according to the metal atom here.
Na: orange, Ba: Red, Pb: Purpule, SB: Antimony.

External Ballistics and Terminal Ballistics
Bullets don’t move in perfect straight lines
Yaw
Precession
Nutation

External Ballistics
Passage through air causes heating – lead softens
Military bullets are metal-jacketed (copper) to prevent deformation

Terminal Ballistics
Bullets cause injury and death by transferring their kinetic energy to target