Forensics Flashcards
Locard exchange principle?
Every contact leaves a trace
The ultimate limit is a single atom
First step in analysing a crime scene?
Alternate light source in the blue range, most effective in producing fluorescence in many substances
What’s chemiluminescence?
Production of light from a chemical reaction
two chemicals form an excited high energy intermediate which breaks down releasing some of it’s energy
Example is luminal - only used as last resort when think have missed everything
How to test for drugs?
Presumptive colour test for drugs
Quick and simple doesn’t require lots of training
Colour tests for drugs?
Marquis colour - amphetamine/methamphetamine
Cobalt thiocyanate - cocaine
Dillie - Koppanyl - Barbiturates
Eriich test - LSD
Duquenois-Levine Test - Cannabis
Colour test for bodily fluids?
Blood - TMB + hydrogen peroxide = green
Also Phenolpthalein = pink
Semen - SAP and Brentamine fast blue = purple
Saliva - starch iodine test - loss of blue colour
Sweat - Ninhydrin = pink
Colour test for gunshot residue?
Modified Greiss test - nitrite compounds = orange
Dithiooxamide test - metal elements, grey-green = copper, Blue pink = nickel
Sodium rhodizonate test - test for lead, = violet
Why reconstruct a crime scene?
It’s lost or destroyed
Depicting events
Explore hypotheses
Present findings
Precautions to take when looking at a reconstruction?
Because it’s on a computer doesn’t mean its right
Colour
Language
Assumptions
Don’t make it up
It is not `always what you see?
It’s what you don’t see
Good method in scaling a reconstruction scene?
Google furniture dimensions
Most important point about presenting to a jury?
Make it very easy to understand
Process of working out a crime scene?
Gather information and intelligence
Asses threat and risk and develop a working strategy
Consider powers and policy
Identify options and contingencies
Take action and review what happened
What happens to the DNA if a body is in the water for too long?
Degrades
Good thing to look out when looking at a body?
If they have had surgery, DNA, taking finger prints, teeth
What hinders investigations?
Investigator pareiodolia
Cognitive bias
Witness imperfect memory
Criminals unwillingness to be caught
Challenges of analytical techniques at a crime scene?
Very small samples = highly sensitive analytical techniques
Evidence is not usually a pure substance (contaminants)
Destructive techniques
Whats qualitative analysis?
Identifying and characterising matter
What is its chemical composition?
Where has it come from? (How did it get there?)
What’s quantitive analysis?
Quantifying the amount of a compound or element present
in a sample
What is the concentration of the chemical?
Is the concentration significant?
What’s preliminary analysis?
- Simple, rapid, inform subsequent tests
Luminol, chemical analysis for biological fluids, gunshot residue, drugs
Types of microscopic analysis?
Optical (diatoms in aspirated water, pollen transfer when concealing a body) and electron (looking at surfaces)
What is separation of molecular spectroscopy?
Assesses electromagnetic properties of molecules and atoms undergoing transitions between energy levels.
Types of chemical analysis?
Molecular Spectroscopy
Elemental analysis
Mass Spectrometry
Chromatography
features of gun shot residue?
When a GSR population is found (at least one three-component particle is identified), a gunshot residue expert can say that it landed there in one of three ways:
The subject/object was in close proximity to a discharged firearm.
The subject/object came into contact with an object that already had GSR on it.
Size of particles depends on firing distance
BUT THIS CANNOT DETERMINE WHO MIGHT HAVE BEEN THE SHOOTER
Looked at with SEM-EDX Scanning electron microscopy used with energy dispersive x-ray (EDX) analysis
Pin impression can help link bullet to a gun
2 Types of useful chromatography?
Liquid and gas
Is mass spectrometry a destructive technique?
yes
Breaking down larger compound into characteristic fragments
Isotope ratio mass spectrometry can be used for?
Identifying fish/meat intake from hair and finger nails
So can identify geographic location
Good non destructive techniques?
UV-vis spectroscopy (paint, dyes on fibres, drugs analysis)
Infrared spectroscopy (looking at electric dipole moment) so looking at which bonds vibrate
What sort of relationship is abosrbanec and concentration?
Linear
What’s used for analysis of individual elements?
Atomic spectroscopy
The Birmingham six case?
Griess test detected nitrite ions and nitro groups
Positive identification on the hands of IRA members
Was found that nitrites could be found in lots of other stuff so they were released
The Jill Dando murder
Killed by close range shot in the side of her head
Found particles of gun shot residue on her head and coat
Similar particles found inside right hand pocket of Barry George seen in the location of the murderer
Then looked at elemental analysis
2008 was found that the evidence was not reliable
Holly Wells and Jessica chapman case study?
girls went missing
Ian Huntley was caretaker at the school
Attempt to burn the bodies and clothes
Analysed fibres
Used comparison microscope and polarising microscopy - distinguish between made made and natural fibres
Showed there had been transferred of fibres between them enough for physical contact
Looked at the soil and pollen from the crime scene
Glenn Turner and Randy Thompson?
She killed her husband and boyfriend
Died from flu then heart failure
It was antifreeze - ethylene glycol - not got rid of by the kidney - found in blood
Stephen Lawrence?
Killed waiting for the bus
Blood stain found in suspects jacket
Nathan Aleen 1979?
Stick of dynamite blew him up in his truck
Atomic absorption spectroscopy
grins test for nitrites
Plastic fragments used to make it allows you to find the manufacture
Test for cocoaine?
Scotts test , Cobalt Thiocyanate
What’s an SIO?
Leader of the team
Principal decision maker in cases of murder, rape, abduction or other serious crime.
Sufficient rank, normally detective inspector, detective superintendent, appropriately trained and experienced.
Responsible for Policy File
What does a crime scene co ordinator do?
Directs the forensic investigation in
Complex major crimes
Major Crimes where there are multiple scenes
There maybe several Crime Scene Managers operating at the various scenes
What does a crime scene manager do?
Directs all aspects of the forensic investigation at the scene of major crimes
What does a Crime Scenes Investigator or SOCO do?
Carry out the tasks identified by the CSM at the scene of major crimes
Deals with all the forensic issues, examinations and recoveries at the scenes of volume or less serious crime
Three tier examination strategy
Photography
Forensic
Fingerprinting
Wound ballisitcs?
A missile has a kinetic energy of 1/2 mv^2
M = mass
v = speed
Missilesproduce a permanent cavity that equals the width of the object during its passage
Shock waves (need to finish this from slide)
tempory cavity?
Types of ballistics?
Internal Ballistics
What happens within the first 2 ms of the shot being fired
External Ballistics
Flight of the bullet or shot after leaving the barrel
Terminal Ballistics
Inside the target or body
Dr Alisdair Dow
Primer composition?
Lead Styphnate Barium Nitrate Antimony Trisulphide Calcium Silicide Zirconium Tetrazine
Primer can be shaped and located in different positions at the base of the round
Describe rifling in the barrel?
Rifling in the barrel
Imparts left or right handed spin to the bullet
Up to 300 000 rpm for military assault rifles
Smooth Barrel
Shotgun
Choke
Gun shot residue analysis?
Scanning Electron Microscopy
Energy Dispersive X-ray Analysis (EDAX)
Atomic Absorption
Inductively Coupled Plasma Spectroscopy
High Performance Liquid Chromatography (HPLC)
Gas Chromatography Mass Spectrometry (GCMS)
Gun shot residue visualisation?
Crime Scene Reagents React with the Nitrates and Nitrites in the GSR – colour change Diphenylamine (DPA) Cotton Swab, DPA and Sulphuric acid Dark Blue Griess Test Photographic paper and glacial acetic acid Orange
What do you need if you find DNA at the scene?
Known suspects for comparison or the database
What are FTA cards?
Contain chemicals that lyse cells, denature proteins and protect nucleic acids from nucleases, oxidative, and UV damage (samples are stable for several years)
Used for offender DNA databases
Blood
Buccal swabs
Saliva
Features of human chromosome set?
23 pairs (46 total) (maternal/paternal) described as homologous as they have the same size and contain the same genetic structure.
Different size and shape, largest denoted 1 etc.
Contain different genes
When chromosomes are stained with fluorescent dyes they develop distinctive patterns of bright and dark bands
What are Short Tandem repeats?
Also called ‘microsatellites’
Forensics uses those that are 2 to 6 bases in length
Less susceptible to degradation so may be recovered after decomposition
Number of repeats is highly variable among individuals (5-20% will share the STR)
100s of different STRs in the human genome
Describe STRs?
Locus = genetic location Allele = versions of the gene at the same location on the chromosome
Each individual will have two copies of each STR therefore increases discrimination
What’s multiplexing?
Primers for many different loci (with STR regions) can all be used in the same reaction mix, will amplify both allele 1 and 2.
Primers are fluorescently labelled to aid detection.
Multiple products will be generated to obtain lots of information with only one DNA template
What does capillary electrophoresis provide?
Each STR product will have a specific label
Different size STR products will be separated from each other by capillary electrophoresis
DNA-17 STR profiling –The National DNA Database (NDNAD) of England and Wales
Established on April 10th 1995 representing 9.6% of the UK population
DNA profile for STR locus and no. repeats?
2 numbers if one from your mother, one from your father
One number if they are the same length
1/2 share parent and sibling
half sibling 1/4
cousins 1/8
How to identify between twins?
Single nucleotide differences can occur every 1:10,00 bp throughout the genome after the blastocyst has split in two.
Hard to detect without full genome sequencing i.e. expensive.
What to do if there is no DNA match?
Predict hair colour, eye colour, skin colour and ancestry
Reduce pool of candidates
What’s irisPlex?
A multiplex genotyping assay and a prediction model based on genotype and phenotype data.
Can predict blue and brown eye colour
What is HIresPlex?
22 SNP’s for hair colour prediction
Four overlap with eye colour
What is skin colour determined by?
Skin colour is determined by concentration of epidermal melanin and therefore number of melanocytes/melanosomes
Reflectance can measure the skin pigmentation
Reflectance M-index (melanin index) is normally distributed amongst the population
How to combine the phenotype measures?
Database enables input of alleles and calculated a predicted phenotype.
Certain SNPs are an absolute requirement due to their key role in determining
Major effectors of facial shape?
Sex: affected the masculinity/femininity of many facial segments
BMI: affected large regions with underlying adipose tissues
Age: affected facial structure due to degrading of skin elasticity.
