A. INTRODUCTION o Procedure in crime scene: Evidence collected from scene by the police -> Evidence are sent to laboratory -> Case assessment by Reporting Officer (come up with strategy for examination) -> Evidence Recovery Unit/Analytical Specialists/DNA Analysis -> Case interpretation/Statement by Reporting Officer -> Court presentation/CJA statement. o Forensic investigation process: Recognition Documentation Collection & Preservation Identification (Physical, Biological, and Chemical Properties) Comparison (Standards, Unknown, Control) Individualisation Evaluation/Interpretation Work at 3 levels: Source: the glass found on the suspect clothing matches the window Activity: the suspect was the person who broke the window Offence: the suspect was the one who committed the offence. Reconstruction Reporting/Presentation o Bertillonage: Anthropometric system of measurements designed to insure the identification of known offenders. o Locards’ Principle of Exchange: Whenever 2 objects meet, there is an exchange of material from each to the other. Random transfer: Incidental or accidental? Control sample: The suspected source of random transfer. o Linkage theory: Physical evidence, victim, suspect, and crime scene are all related to each other. o 3 issues in sampling: Sample Continuity: Chain of evidence. Like passing the evidence from collection to analysis to production in court. Each person who holds the sample should provide statement, which include the time and date that a sample was delivered to a second party and the identity of that person. Issues -> Integrity. Has the sample been tampered? Sample Packaging: This is the medium used to transport and store samples. Packaging should be suitable with the sample. For fire debris, suitable packaging is made after a consideration of sample size, sample loss (evaporation), potential of contamination, and possible solvent effect. Sample Selection: This refers to sampling site and the number and size of the samples selected. Issue -> How do you choose which sample is necessary and which sample is not? Sample chosen should be able to maximise the opportunity for the recovery of material with investigative and/or forensic value. o Why preserve scene? To prevent material from being added into or carried out of the scene, destroyed within the scene, or unnecessary handling of material. o Scene Evaluation (Prior to any physical disturbance of the scene): Recording Ambient temperature Scene security (scene guards, scene logs, cordons, RV points, etc) Descriptions (scene, body, weapons, clothing/disturbance, conditions of contents) o Initial action (stabilising the scene when you first arrived):
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Take immediate action to save or prevent loss of life. Confirm that a crime has been committed and introduce your cordons Every witness at the scene are potential suspect. Do not allow them to re-enter the scene. If potential suspect or witness is at the hospital, send an officer immediately. 3 ways to enter scene that gives reasonable certainty that it won’t destroy relevant marks: Corridor should be examined for footwear. This process should be done first before anyone else goes through this corridor. Bridges or stepping plate can be used to protect the floor Choose a route which is unlikely to be chosen by the offender. Searching for evidence method: Zone Method: Scene is divided into four squares area. Circular Method: Do thorough searching in a circular pattern starting from the inside to the outside. Strip Method: Search scene in an ‘M’ line. Line Method: This method is best for large areas. Put strings in area. Searchers move parallel to one another. Golden Rules of Contamination Issues: Isolate person from other (Suspects, victims, and witnesses) Do not allow that person to eat, drink, wash, etc. A different officer must deal with each suspect The same vehicle must not be used to carry victim and suspect until they are examined. The same room should not be used for the examination Doctor examining victim and suspect should be required to change protective suit. When removing clothing from people have them stand on sheet of paper. Item removed must be packed separately Wet clothing should be put into open polythene bags and dried by laboratory staff or trained officers. Do not test tools found on suspect with marks at scene. Packaging exhibits: Samples should be packaged, sealed, labelled, and documented after collection Clothing, shoes, and vegetable matter: Pack in paper bags Powders, paint flakes, and other granule material: Put sample in folded A4 paper. Place paper in polythene bag. Blood for grouping/DNA, saliva, swabs: Freezer Knives and tools: Manufactured rigid knife tubes
B. SCIENTIFIC EQUIPMENT o Gas Chromatograph-Mass Spectrometer: Used to separate component of some mixtures. Consists of an injector, column in an oven, and detector. How it works: Sample is injected into heated injection chamber in liquid form where it is vaporised, unless it is injected in gas form. Sample is carried by the mobile phase (nitrogen or helium) through heated column containing stationary phase. The heated oven makes component leaves the column in sequence.
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As the separated component leaves the column, the detector send signals to the computer which produces graph which represents the quantity of detected component and the time component left the column. Several components could be present in one peak, therefore the content of each peak is passed to the mass spectrometer where contents are bombarded with a stream of electrons that break up and ionise the molecules. The instrument separates the ions and there is a graph produced that represents each peak from the GC. Thin Layer Chromatography: Separate mixture of a component on a flat plate. Used to analyse fibre dyes and controlled drugs (cannabis in particular). Stationary phase is flat plate bound with silica or alumina. Place sample in a bottom spot of the plate in a marked position. Place plate vertically in a closed tank filled with shallow pool of liquid (mobile phase, the solvent). Liquid should not come to direct contact with sample on the plate. Solvent gradually rises through capillary action. Components of sample become separated. This process is called development. Before solvent reaches the top of the plate, plate is removed from the tank. Marked the boundary line of the wet part and dry part on the plate. Dry the plate. The separated components of the mixture appear as individual spots on the record. These spots could be made visible using appropriate treatment and equipment. Scanning Electron Microscopy: Uses electrons to visualise and magnify samples up to about half a million times. Fourier Transform Infra-Red Analysis (FTIR) & Microspectrophotometry: Used to discriminate fibres. FTIR exploits that most synthetic fibres are carbon based polymers. Atomic bonds between carbon and other atoms asor infra red radiation. Wavelength differs depends on the atom. The instrument detects the absorbance at each wavelength and can discriminate between fibres that have very small atomic differences. MSP is similar but operates across the visible light spectrum and can therefore be used on all fibre types. Comparison Microscopy: Comparing two items by joining two microscopes together and splitting the view in the eyepiece between them. Used for comparing hairs, fibres, paint fragments, etc.
C. HAIR EVIDENCE o 6 types : Head: Generally circular and often split at the end Eyebrows and eyelashes : circular in section with tapering ends Beard : generally triangular in section Axillary (underarm) : oval in cross section Pubic : oval or triangular in cross section with a tendency to curl o Parts of hair : Cortex : Major portion of most hairs. Cuticle : The outer scaly layer of a hair, composed of flat overlapping cells or scales. This part maintains hair’s structural integrity, prevents hair from breaking away in
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small fragments, prevents the transfer of soluble substances from outside to inside the hair. Medulla : The central ore of a hair. Medulla index : The ratio of the diameter of the medulla of a hair to the whole diameter of the hair. Phases of hair growth : Anagen: The phase of active growth. 85-95% of hair follicles are in anagen phase. Where hair is naturally shed, such as through combing. Catagen : Regression phase of the growth cycle. At the end of anagen phase, hair stop growing and moves into catagen stage involving an upward movement of the hair root which becomes bulb shaped. Catagen only lasts about 2 weeks. Less than 1% of the hairs are in catagen. This is the transitio from anagen to telogen. Follicle is inactive. Telogen : Resting stage. Once catagen is complete, hair just moves to telogen without noticeable changes until anagen begins again. During this phase, hair is attached int e follicle only by the club and naturally falls out. Different areas of hair collection: Head : Samples from this part should be obtained as soon as possible as head hairs change over time. Obtain at least 25 full length hairs including both plucked and combed hairs, packaged separately. Pubic : Sample taken a year or moer after a crime may still be suitable as pubic hairs are not subjected to much changes over time. Sample obtained should be 25 ful length hairs from different areas of the pubic region.
D. TEXTILE EVIDENCE o 2 principles of fibres : Textile fibres can be exchanged between 2 individuals, an indvidual and an object, and between 2 objects. Whether a fibre is transferred and detected is dependent on : The nature and duration of contact between the suspect and the victim The persistence of fibres after transfer The types of fabric involve in contact. o 4 factors of comparison when identifying using fibres : Mechanical fit : When fabric is torn (this is conclusive evidence). Microscopic comparison : colour, diamater, striations Colour cmparison of specific dyes used with MSP or chromatography. Chemical composition : make sure fibres are from te same generic class and subclass with infrared spectrophotometry. o Evidential weighting factors of fibre : Fibre number : The number of fibres on the clothing of the victim found matches the clothing of a suspect is important in determining actual contact. The greater the number, the more likely that contact occured. Fibre location : the location of fibres on diffrent areas of the body or specific items at the crime scene influences the significance of the fibre association. o Shedding : Tightly woven or knitted fabrics shed less often than loosely knit or woven fabrics. Fabrics composed of filament yarns shed less than those composed of spurn yarns. Age of fabric affects the degree of fibre transfers.
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Newer fabrics may shed more due to the abundance of loosely adhering fibres on the surface. Damage to a fabric caused by physical contact greatly increases the likelihood of a fabric transfer. Secondary transfer : One caused by contact between two items in which material on one item presents itself as a trace contact material, is transferred to the econd recipient item. Subsequent tertiary transfer : An indirect transfer involving the donor item as an intermediary surface. Fibre taping : Method to colet out of place fibres. Clear strip of adhesive tape is dabbed onto the object. Adhesive is then place side dow onto clear acetate, sealing in and preserving recovered fibres.
E. DNA IN CRIMINAL INVESTIGATIONS o Where can you find it ? Blood, semen, vaginal cells, skin & tissue samples, hair roots, envelopes, cigarette ends, chewing gum. o Why does forensic sceince use DNA ? Detectable pattern that are repeated a number of times that are characteristic of the individual. DNA could survive well under a wide range of environmental conditions. DNA can survive for centuries. DNA could be isolated from any of a whode variety of biological samples likely to be left at crime scene. DNA could e retracted from any source. It will still produce the same pattern. Extremely sensitive and precise technique to detect pattern from very small samples are available. Techniques are relatively cheap and rapid to carry out. Data generated are readily assembled into a database, which can be searched for a given DNA profile and therby identify individual from DNA sample. o Definitions of parts of DNA : Genes : Information of individual characteristic. E.g. blood type and eye, hair, and skin colour. Allele : Forms of a particular gene. Genotype : The combination of genes and alleles of those genes carried by an individual. Nucleotides : The building blocks of te nucleic acids DNA and RNA. Base pairs : An association between the bases of hte nucleotides on opposite strands of the DNA double helix. Hydrogen bonds link the bases. (A-T, C-G). o Regions of DNA : Coding DNA is not analysed in profiling. Non-coding DNA is analysed in profiling. o DNA Profiling : Short tandem repeat : The length of repeat is short. Only between 1 and 4 bp. This is very sensitive and results can be obtained within 48 hours. Tandem repeat : A short sequence of DNA repeated consecutively a number of times. Polymerase Chain Reaction : A means to amplify and copy a particular region of DNA to produce a large amount of it. Specifuc, fast, and extremely sensitive. The
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process of replication in which each strand of the double helix serves as a template for the synthesis of a new strand Multi-locus profiling (MLP) : Cutting DNA then separate the according to size. Single Locus Profiling (SLP) : Targets single locus of interest. Highly discriminating. Results suitable for data-basing. Procedure of DNA profiling : Collect and store evidence from the scene Extract DNA from sample Quantify the DNA Amplify the genetic loci to be examined Seperate and amplify DNA according to size using electrophoresis Interpret the pattern of alleles produced Compare one or more DNA samples for a match Present the data in the context of other evidence. Type of crime samples : Blood : A good source of DNA. Quantity required for analysis gradully reduced over the years. Minute stains (1 mm in size) can be analysed. Age of stain will contribute to success. Saliva, cig ends, chewing gum, drinking vessels, balaclavas, envelopes/stamps, partly eaten food, DNA present in mout cells but not saliva. Hair : Results can be obtained from a single pulled hair root (e.g. hair cuaght between surfaces), however roots of fallen hairs are dead and not suitable for STR profiling. Nasal secretions : Used handkerchiefs with obvious deposits. Sweat : Sweat in particular does not contain cells. Certain areas of clothing may contain mixture of sweat and skin cells and can be analysed. Others : Urine, faeces, dandruff, bones are not suitable for STR profiling. For sexual offences : Semen (DNA obained from cells shed during ejaculation) and vaginal secretions. Mitochondrial DNA : Found in every cell of the body. This type of DNA is inherited only from the mother.Can be used on bones, faeves, and hair shafts that have been degraded.
F. GLASS EVIDENCE o Soda lime glass are the majority of the glass manufactured around the world. Usually used for windows, bottles, and drinking glasses. Made from sand (silica), soda ash, limestone (calcium carbonate), and cullet. o Common properties of glass : hard, elastic, brittle, non-conductors of electricity, chemically stable. o Type of glass : Flat glass : Manufactured with the Fourcault process. Components are melted in a large tank (which little by little dissolved itslef into the molten glass) so traces of tank are present in product. The sheet of glass is then drawn vertically through a slotted refractory in continuous ribbon. Float process : Molten glass is delivered onto a bed of liquid tin where the glass floats over the metal
The rollers on the sides pull the glass to a desired thickness depending on the speed of the pull Toughened glass : Flat glass may be processed by tempering. Also called toughening. Temepering is achieved by rapid cooling of heated glass Product is called safety glass. Breaks into diced pieces that do not have sharp or pointed edges. Laminated glass : Inserting a sheet of plastic between two sheets of flat glass. Known for their ability to resist penetration, acting as security glass or to restrain passengers within a vehicle during collision. Glass evidence terminology : Concentric cracks : fractures forming in an approximately circular pattern around the point of impact. Cone or crater : funnel shaped area of damage caused by high velocity impact. Hackle : line on the crack surface running parallel to the local direction of crack spreading. Radial cracks : fractures extending outward from the point of impact. Caused by low vleocity shots or larger missiles, stones, etc. Caused ‘Reaward Fragmentation’ (fragments forced backwards and lodge in clothing or in hair). Wallner lines : rib shaped marks with a wave like pattern. Ways to break glass : high velocity impact, medium to low velocity, explosive percussion, heat. Glass is strong in compression, but weak in tension. 3 ‘R’ rule : Radial cracks form -> A right angle -> On the reverse side -> of the force Nelson and Revell’s study : Fragments were projected as far as 3.3 m. A stroke in the middle of a pane produced more fragments than a stroke in a corner. The faster the pendulum, the smaller the hole and the fewer fragments were produced. Analytical techniques : Immersion : Measuring the density Refraction : The bending of light. Chemical impurities. Porperties of matter : Chemical properties :
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