Forensic Science Flashcards
Define a crime scene.
The scene of an incident irrespective of whether a criminal or illegal action has been established at that time.
Describe the role of a First Attending Officer (FOA)
An FOA must: Evaluate the Scene.
Ensure the safety of any witnesses to the incident.
If they think a crime has been commited, decide on the level of backup/force to bring in to help with the investigation.
Establish the 6 Ws Why What Who When Where How.
Describe the importance of Control at a crime scene.
Control is essentially controlling the access to a crime scene in order to prevent contamination of the area. A common approach path is set up in order to prevent contamination of the scene and the route should avoid areas where the criminal is suspected to have ben. as much as possible.
Describe the role and importance of preservation at a crime scene.
Preservation at a crime scene essentially means keeping the crime scene as close to the same condition as it was found. Protective suits will be worn by all investigating officers in order to prevent contamination from DNA or any fibres from their clothing. A tent may be used to prevent environmental degradation if the scene is outside.
How is physical evidence preserved.
to help preserve physical evidence secure packaging is used i.e. sealed bags or containers in order to prevent anything else coming into contact with the item which could damage finger prints or DNA evidence present on the item.
How would tire tracks or footprints at a crime scene be preserved?
Photographs or Casts.
Describe a chain of custody.
Begins with the evidence being logged into a secure location, the name of the person who collected the evidence and subsequently logged it in is recorded and signed for. The location the evidence was collected is recorded as is any other place it has previously been stored. Anyone who wants to access the evidence after it has been securely stored must sign for the evidence when they access it, the date and time will also be recorded.
Describe the importance of record and recover in reference to crime scene evidence.
Records are extremely important for legal reasons, mishandling of evidence could result on a criminal walking free due to a clerical error. They are also important for the reconstruction of a crime scene at a later date if this could be helpful to the investigation. Thorough records of witness statements, crime scene photos and initial notes on the scene may all be important evidence in a trial so keeping detailed accounts of this information is of high importance.
Describe some methods of recording fingerprints.
Finely ground aluminium powders are commonly used to locate fingerprints, the powder will stick to the residue of the print enhancing the visibility, an impression of the print is then recorded. Black lights may also be used to locate fingerprints and photographs may also be used to record them.
What is the difference between fingerprints and finger marks.
A fingerprint would be the ideal or perfect scenario in which the full fingerprint is transferred perfectly onto a surface. at a crime scene this is very rarely the case however and a finger mark is what would actually be found, finger marks are often smudged, partial or unclear.
Describe how powder suspension is used to enhance finger marks.
Powder suspension technique can be used to enhance finger marks on non-porous surfaces. it is the suspension of a finely ground coloured metal suspended in a detergent solution. Firstly a brush is dipped in the powder suspension solution and then applied to the surface in a similar motion to applying paint Once the surface has been coated the solution is washed off leaving it only in the place of the finger mark.
Describe how powders are used to enhance finger marks.
Powders ae used to enhance finger marks on non-porous surfaces, they are simply metallic dust which are applied using a brush or magnetic brush. different powders are used on difference on surfaces, aluminium is more effective on glass and black magnetic powder is best for use on upvc. Once enhanced the finger marks can be recorded by photography or lifted off using finger mark tape which is subsequently attached to clear acetate.
Describe the ninhydrin method of recording finger marks.
ninhydrin is a chemical solution used to enhance finger marks on a porous surface such as paper or cardboard. the surface is washed with the solution and left to dry before being placed in a 70 degree humid oven, the solution reacts with amino acids in the finger mark to produce a purple coloured mark which can be photographed using appropriate filters.
Describe how cyanoacrylate can be used to enhance and record finger marks.
Cyanoacrylate (superglue) fuming can be used for non-porous surfaces, the vapour given off may react with some finger marks. The object is placed in an oven which controls temperature and humidity and allows a vapour of the cyanoacrylate to attach to the finger mark ridges forming a white crystalline substance. this can be dyed using fluorescent dyes or powders to enhance the finger mark.
What are the two types of finger marks?
Visible: no enhancement needed can be easily photographed comaninly a contaminant e.g. blood. Latent: Enhancement needed Invisible.
What are the three main glands responsible for perspiration associated with finger marks.
Eccrine Glands - most common in extremities i.e. hands and feet.
Apocrine Glands - found in hair follicals.
Sebaceous Glands - armpits
What is the name of the fingerprint database in A. The UK
B. The US
A. Ident1
B. APHIS
ACEV method of fingerprint identification.
A - Analysis: Analysis of all variables to the fingerprint e.g. the deposition surface, enhancement process, pressure and distortion, quantity and quality of the latent print ridges affects the next stage.
C - Comparison: comparing the fingerprint to another set of fingerprints which are already recorded e.g. that of a suspect, compares the varios features present within the overall patterns
E - Evaluation: 3 options, Firstly the examiner may conclude that yes the finger mark matches the fingerprints in the database and they were made by the same finger on the same person. Second the examiner may conclude that the fingerprint does not match the one the database gave out. third the examiner could conclude that the results were inconclusive due to lack of clarity.
V - Verification: all examinations must be verified by a second experienced examiner.
Describe 1st level detail of a fingerprint.
Overall fingerprint pattern
Loop patterns are most common
may be genetically determined.
Describe 2nd level detail of a fingerprint.
Specific ridge characteristics (minutiae) and their location, there are over 100 minutiae in a single fingerprint.
describe 3rd level detail of a fingerprint.
Examination of pores and ridges.
How many genes are there in the human genome?
20-25,000
8% of the genome consists of repetitive DNA sequences or tandem repeats of nucleotide sequences, around 10,000 have been identified. they are characterised by the identity and number of nucleotides in the base sequence. some have alleles that code for the number of variations in that sequence.
what are the most important gene sequences used in forensic DNA analysis?
STRs (Short tandem repeats) are the genes used for DNA analysis, they are most commonly repeating sequences of 4 nucleotides.
how is the angle of impact of blood dropping onto a surface calculated?
Dividing the width of the stain by its length to give the sine of the angle.
Who developed the PCR technique used for DNA replication .
Kary Mullis
What type of stain will drops of blood falling vertically produce?
A round stain.
What type of stain will blood striking a surface at an angle produce.
An elliptical stain with a tail.
The blood and tail shape will show the direction the blood was travelling, the ellipse narrows as the angle of impact becomes more acute.
How can you estimate the point of impact from blood stains?
Connecting blood spots with string will show the strings to converge at a single point, this is the point of impact.
Wounds gained from a high force impact such as a bullet will produce what kind of blood spatter?
smaller and freely dropping blood, the more force the smaller the spots of blood.
Describe a positive and a negative bloody footwear mark.
A negative footwear mark is obtained when someone steps into blood leaving an imprint from their shoes in the blood pool. a positive footwear mark is obtained if this person then steps out of the blood and leaves an imprint of their shoe on the floor.
What can bloody footprints help tell us about a crime scene?
WHO - Whose shoe was it that left the mark?
Where - Where do the footprints lead i.e. where did the potential suspect go
WHEN - the blood must have been liquid at the time so this person was present near the time of the incident.
What can cast offs tell us?
They can show the direction that a blade was swung, vertical or lateral strikes.
What are voids?
Voids are gaps in blood spatter that are created by the attacker shielding the wall or surface from the blood, i.e. the blood hit the attacker instead suggesting that there is evidence on the attackers clothes somewhere.
What gives blood its red colour?
Red blood cells (erythrocytes).
What are the three main cells that blood is composed of.
Red Blood Cells (Erythrocytes)
White Blood Cells (Leukocytes)
Platelets (Thrombocytes)
How many erythrocytes are there in blood per microliter and what is unique about them?
5 million erythrocytes per microliter of blood
They have no nucleus.
How many leukocytes are there per microliter of blood? What do they do? How can they be further defined?
9000 they produce antibodies they are larger than erythrocytes. granulocytes lymphocytes and monocytes they are the source of the DNA used for DNA profiling.
How does the body form clots.
fibrinogen converts to fibrin which traps platelets to form a clot and stop bleeding
How would you initially test for blood if you suspect it may be present on a surface?
Swap with dry filter paper and then add casomere presumptive test reagent and hydrogen peroxide, if a strong pink colour rapidly presents this is a positive test for blood. some vegetable material will also display this.
What are the basic steps to follow when generating a DNA profile.
Screening Test
DNA extraction
STR amplification
Amplicon separation alleles are identified
Profile generation, profile contains the alleles.
Describe the amplification step.
Firstly the quantity of DNA present is recorded as the amplification is sensitive to the quantity of DNA present. quantitative PCR is used to replicate the DNA, the extract is diluted and introduced to an instrument called a thermal cycler along with the required reagants for the STR amplification step, the amplified product is introduced to an instrument called a genetic analyser fro separation of the STRs by a procedure known as capillary electrophoresis . the genetic analyser also identify the STRs present.
What are Primers
Primers are short nucleotide sequences complementary to the nucleotides that lie either side of the target STR.
What is directionality?
3 prime and 5 prime are used to describe the end to end orientation of a DNA strand. these refer to the orientation of the hydroxyl groups in the sugar in the dna backbone. The new strand is synthesised in the 3 prime to 5 prime direction.
What is a thermal cycler?
A device that can rapidly heat and cool a sample to a precise temperature.
What is taq polymerase?
Taq polymerase is the dna polymerase used in the pcr reaction as it can resist high temperatures.
What is the amplicon?
Amplicon is the product of the PCR reaction.
What are the 3 steps of the replication?
- The DNA is heat denatured into separate strands
- The sample is cooled and the primers anneal to their complimentary sequences at the 5 prime ends
- The temperature is then raised and the taq polymerase extends the primers.
why are dyes used.
To allow multiple STRs to undergo the PCR reaction in a single run.
why can the PCR reaction not be repeated on the same STR more than 30 times?
The reliability of the process becomes to small to be valid hence there is a limit of 30, this should provide a large enough sample to allow accurate DNA profiling.
How many STRs would a standard DNA Profile be composed of?
20
At the end of a PCR there is a large mix of amplicons and reagants and which must be separated into the individual STRs. How is this done?
This is carried out by capillary electrophoresis which relies on the size of the STRs being identified snd being able to distinguish between the STRs by the use of dyes. An electric current is the driving force behind the separation process. Software as part of the equipment is able to identify the individual STRs and can identify the alleles for each STR.
What are the most important types of DNA relevant to forensic analysis.
Mitochondrial DNA
Y chromosome STRs
What is significant about mitochondrial DNA?
Mitochondria contain DNA which display structural variations which are inherited so it can be used as a genetic marker.
The main mole of mitochondrial DNA is coding for genes involved in energy metabolism.
What are the 3 types of firearms?
Long guns, Hand guns and machine guns.
What are the components of a cartridge?
Projectile, propellant, primer and case.
What is the definition of a firearm?
An object which is sealed at one ednand fires some form of projectile.
What questions would a forensics expert be expected to answer in a firearms case?
They could be expected to identify: what kind of firearm was used, the number of shots fired and their direction, the firing circumstances. also to determine if a specific firearm had been used and comment on who may have fired the weapon.
what is the common propellant smokeless powder made from
nitrocellulose, nitroglycerin and carbon powder.
what is the primer used for?
To ignite the propellant.
What happens at the moment of firing?
A firing pin strikes the bottom of the cartridge causing the primer to detonate and ignite the propellant the burning propellant forms hot gases at high pressure which expand the case to seal the breach the pressure forces the projectile and hot gases out of the gun.
how can the gas discharged form the gun help determine the firing circumstances.
When fired the gases are expelled in a cone like shape and can leave scorch marks and can leave residue from the propellant for handguns up to 60cm and for rifles up to 2m, at closer distances the diameter of the scorched area can be used to estimate the range.
Name the 4 classifications of tool marks and give an example of what instrument could cause each of them.
Impressed mark - screwdriver being used as a lever
Crushed mark - pliers cutting a wire
Striated mark - a screwdriver scraped across a car door
Multi-stroke mark - a saw being used to cut wood
How can tool marks be recorded?
Tool marks can be casted using a silicon based material known as copyright to take an accurate copy/impression of the tool mark.
What does the term rifled barrel mean?
A rifled barrel refers to a set of spiral grooves that run from the chamber to the muzzle that grip the projectile causing it to spin which helps increase the range and accuracy
What are rifling marks classed as?
impressed toolmarks, they can indicate a particular type or brand of firearm but not a specific firearm.
What are class characteristics?
Generic characteristics present from the design and manufacturing process, characteristics common to all tools of that type e.g. size of a screwdriver blade, size of a projectile, diameter of a barrel.
What are individual characteristics?
These ae characteristics specific to a particular tool, these are produced by damage in use of the tool e.g. wear on the jaws of pliers, the ejector on a cartridge case or the barrel on a projectile. they are caused accidentally during use. these can be used to identify if a particulasr tool caused a particular tool mark.
How can footwear marks and tire marks be recovered?
photography is the most important for footwear marks, a cast of the mark may also be made or the actual mark itself can be lifted using specialist equipment depending on the material the mark was made in.
name the 3 classifications of drugs and give an example of each.
Natural - plant products cannabis
Semi-synthetic - cocaine
Synthetic - Meth
What is the potency by weight of cannabis leafs?
0.5g - 5%
9g - 25%
What is the potency by weight of cannabis resin?
2g - 10%
What is the potency by weight of cannabis oil?
10g - 30%
What percentage of the world aged 15-64 regularly smoke cannabis
3.9% 186.4 million people
What is the active part of a semi synthetic drug molecule known as.
Alkaloids
What is the alkaloid present in cocaine?
Tropane
What is the alkaloid present in Opiates such as heroin?
Isoquinoline
who first extracted cocaine from the coca plant?
albert neeman in 1860 for use in medicinal products.
List some side effects of cocaine abuse.
Increased risk of stroke insomnia asthma chest pain increased risk of infarction to heart.
who first synthesised heroin?
alder wright in london
List some side effects of heroin abuse.
Increased risk of pneumonia
collapsed veins
What was cocaine used for prior to recreational purposes?
some medicinal uses such as toothache drops and a cure for dandruff, was in original recipe coca cola, 9mg per glass, also present in tonic wine.
What is the alkaloid for amphetamines?
phenethylamine
when was methamphetamine first synthesised?
1893 by nagi nagayoshi
1919 was the first time the crystalline form was produced.
What was it originally used for?
given to armies to keep pilots and soldiers awake during world war 2 and was known as pervitin. was given to Japanese factory workers to increase productivity.
what are the side effects of crystal meth abuse?
insomnia aggressive behaviour sweating and numbness of the skin. basically damages everything meth mouth may induce heart attacks
what can methamphetamine still be prescribed for today?
Obesity that is outwith the persons control.
Name drugs classed as psychotropic substances.
Phenethylamine
hallucinogens
benzodiazepines
barbiturates
Name drugs classed as narcotic substances.
Fentanyl
opiates
cannabinoid
cocaine
Name substances classed as precursors.
Ephedrine
Pseudoephedrine
safrole
acetic anhydride.
Name the 3 main drug related legislations and describe them.
The misuse of drugs act 1971 - lists all controlled substances in classes A,B,C it also details the offences around these drugs e.g posession
Misuse of drug regulations 2001 - provides liscensing for the production possession and supply of these controlled substances, they are listed in 5 schedules depending on therapeutic usefulness and ability to cause harm
Drug trafficking act 1994 - it is illegal to smuggle drugs and allows the confiscation of monies obtained from these actions.
Steps in the analysis process of a substance weighing more than one gram
- physical description
- Sampling - must be representative depending on the quantity seized
- presumptive colour test can quickly identify the class of drug
- thin layer chromatography
- Instrumental analysis
confirmatory tests, double testing to confirm the results, gas chromatography and mass spectrometry
What is drug profiling?
The use of methods to define the chemical and or physical properties of a drug seizure for comparing seizures for intelligent (strategic and tactical) and evidential purposes.
What are the steps for drug profiling?
- identify the sample
- identify a common origin
- link this to a clandestine laboratory
- identify dealer-user network
