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.
