Forensic Past Questions

What is a grid search?

• used in large areas and is an advance on the strip method

• searchers having completed the latter search are doubling back perpendicularly across the area being search

• it is more time consuming than the strip method but it is very methodical and thorough as it is searched from two different point of views

• each square is assigned an number or letter

What is a spiral search?

spiral search is carried out by a single person

involves the searcher walking in a circular fashion

starts from the outermost boundary towards the central point of the cordoned off area

do not start in the center as vital evidence may be destroyed while walking towards the central point

Describe the principle of HPLC and outline the components of a HPLC

• high powered liquid chromatography

• it speeds up the process of LC by use of a pump

• the column in which the sample flows through and separates into components

• a constant-flow pump to pump liquid through the column

• a reservoir must be provided to assure a consistent supply of mobile phase

• a rotary injection valve is where samples are introduced

• a detector is used to monitor the presence of sample compound as they come off the column

• a data system is required to collect and interpret the result

• a HPLC chromatogram is produced by the data system

outline steps involved in a crime scene preliminary survey

• the search surveys the entire scene to ascertain what types of evidence should be looked for

• the nature of the crime scene offers the firsts clue of the type of evidence that may be obtained

• physical evidence - can range from large objects to microscopic traces

• crime scene is recorded in its untouched state

• items of physical evidence are photographed where they are found

• dimensions of the crime scene are sketched having been measured

• positions of the body are carefully noted in serious crimes

Name four categories of drugs based on their physiological effects and two examples of drugs in each category.

Narcotic drugs, Hallucinogens, Depressants and Stimulants

• Narcotic drugs implies a state of lethargy, they relieve pain or induce sleep and are high addictive

examples include heroin and opium

the main source is opium with is a milky juice from an unripe poppy pod

• Hallucinogens cause alterations in mood, attitude and perceptions

examples include marijuana and LSD

both do not cause physical dependency

• Depressants are drugs that slow down the CNS

they act as a sedative and referred to as downers

examples include alcohol and tranquilizers

• Stimulants are referred to as uppers or speed

they cause a sensation of flush followed by intense feelings of pleasure

examples include amphetamines and meth

two color tests used in the preliminary analysis of drug analysis

• Marquis Color test - turn purple in the presence of heroin and morphine, orange and brown in the presents of meth and amphetamines

• Van Urk test - blue-purple in the presence of LSD

• Dillie-Koppanyi - screens for barbituates and turns violet-blue

principle of forensic serology as it relates to ABO and Rhesus blood grouping system

• serology is the scientific study of blood serum and other bodily fluids

• it refers to the diagnostic identification of antibodies in the serum

• it comes from the word serum - includes initial exam of blood, bloody typing and genetic analysis

• antigens are found on the surface of red blood cells

• Type A blood had A antigens

• Type B blood had B antigens

• Type AB blood has both A and B antigens

• Type O blood has neither antigens

• if serum containing Anti-B is added to red blood cells that have B antigens, then the antibody binds to the antigen on the cell surface

• Agglutination - each antibody can attach to different red blood cells so a network of cross linked cells is created

• Antibodies against A and B antigens can be used to determine the ABO type of a blood sample

• Presence or absence of agglutination when antibodies are added to blood determines blood group

• A blood sample is tested with anti-Rh serum.

• If agglutination occurs, the blood is Rh-positive.

• If there is no agglutination, the blood is Rh-negative

morphology of a hair shaft

has three main layers - cuticle, cortex and medulla

• cuticle is the outside covering of the hair

• hair is resistant to chemical decomposition and retains its structural features over a long period of time due to the cuticle

• made up of scales that point towards the tip of the hair

• cortex is the layer of cells within the cuticle

• contains pigment granules which gives hair its color

• color, shape and distribution of granules is used to compare hair from different individuals

• examine microscopically in a liquid medium to allow max light to penetrate the hair

• medulla is the collection of cells that looks like a central canal running though the hair

• in animals, the diameter is more than ½ the hairs diameter

• in humans the diameter is 1/3 and fragmented or absent

identification and comparison of hair based on morphology

• in animals, the diameter is more than ½ the hairs diameter

• in humans, the diameter is 1/3, fragmented or absent

• comparison microscope is used

• look for matches in color, length and diameter

• presence or absence of medulla and distribution

• shape and color intensity of pigment granules of the cortex

• dyed color is present in cuticle and the cortex

limitations of hair as crime scene evidence

• usefulness is limited

• is it not possible to determine if hair originated from a particular person on the basis of exam based on morphology

• hair has poor discriminatory power

• is DNA is obtained from cells in the hair root and makes it valuable evidence

state four ways to identify an accelerant initiated fire

• evidence of separate and unconnected fires

• evidence of streamers to spread fire from one area to another

• presence of containers capable of holding an accelerant

• presence of ignition device

• existence of irregular shaped pattern on floor from pouring accelerant

difference between low explosive and high explosive and examples of each

• speed at which explosives decomposes varies and classified as high and low

• low explosives are black and smokeless powder

• only ingredients are fuel and oxidizing agent

• only explosive and lethal when confined - pipe bomb or containers

• high explosives detonate almost instantaneously at rates from 1000-8500 meters per second

• supersonic shock wave is created

• smashing and shattering effect on the target

advantage of analyzing mitochondrial DNA compared to genomic DNA

• Mitochondrial DNA comes from the mother

• if reference sample from the victim is unavailable, sample can be taken from any maternally related relative

• Genomic DNA is the material found in the nucleus and contains three billion base pairs of DNA

• useful for studying a wide range of genetic traits

limitations of analyzing mitochondrial DNA when compared to Genomic DNA

• Mitochondrial DNA has a small genome size therefore it contains less genetic material and fewer markers than genetic DNA

• Genomic DNA analysis is time consuming and expensive due to the complexity of sequencing and analyzing the large genome size

describe VNTR DNA profiling

• VNTR stands for variable number tandem repeats

• portions of DNA contain sequences of nucleotides that repeat numerous times

• the number of tandem repeat sequences differs from one individual to another and offer meant to distinguish between individuals

• all humans have same type of repeats but have a large variation in the number of repeats at different regions in the genome

limitations when VNTR is compared to STR

• VNTR are too long to be amplified by PCR

• STR are used for PCR analysis

• STR by PCR is faster than VNTR analysis

describe the principle and applications of mass spectrometry and outline the key components of MS and state what is on the axis of the mass spectrum

• mass spectrometry is a technique used to determine extremely accurate mass of molecules

• materials enters a high vacuum chamber where a beam of high energy electrons is beamed at a sample molecules causing them to lose electrons and become positively charged

• ionization to bring a molecule from a liquid or solid phase into the gas phase for measurements and analysis

• ionization leads to fragmentation - positively charged molecules are unstable and decompose into numerous smaller fragments

• x-axis = m/z

• y-axis = relative abundance

the main components of Gas Chromatography instrument and the process by which sample components are separated and identified

• separates mixtures on the basis of their distribution between a stationary liquid phase in the column to a moving gas phase

• a gas stream is fed into column at constant rate

• sample is injected as liquid and immediately vaporized and swept into column by carrier gas

• column is heated in an oven to keep the sample in its vapor state

• components in the sample travel at high speeds determined by their distribution between moving and stationary phases

• as components emerges from the column, they enter a detector which generates electrical signals - recorded onto a chart called a chromatogram

how pyrolysis Gas chromatography differs from conventional Gas chromatography and an example of a sample analyzed in each

Sample preparation

• PyGC involves breaking down the sample at high temperatures whereas CGC analyzes the sample in its intact form

Separation:

• PyGC separates the volatile and semi volatile products produced by pyrolysis whereas CGC separates components based on their boiling points and affinities for the stationary phase

Samples by PyGC = microplastics, paint and textiles

Samples by CGC = petroleum, food and pharmaceuticals

Fundamentals of fingerprint analysis with reference to the three main components, common ID points and process of primary classification

• three main components are ridges, valleys and core

• ridges are the raised lines - can be circular, loopy and whorled

• valleys are the depression between ridges - can be deep shallow or non existent

• core is the center of the print - circular or oval shaped

• common ID points are dots and crossovers

• dots are the small, isolated dots on the ridges

• crossover are where two ridges cross over each other

• visual inspection - examine the fingerprint to determine the pattern type

• ridge patterns are circular, loopy, whorled or arched

• core can be located and determine the shape and size

handwriting analysis referring to exemplars

• questioned documents is one where the authenticity of the handwriting is in doubt - this can include letters, cheques and wills

• an exemplar is a sample of handwriting to which questioned document is compared

• unconscious handwriting of two individuals are never identical

• there are variations associated with mechanical, physical and mental functions make it unlikely that they can be exactly reproduced by two individuals

• writer should use pen and pencil similar top the questioned document

• writer is not shown the questioned document or told how to spell certain words, when to capitalize etc

• suspect must write the dictated text three times to reveal any attempts at disguising writing

• dictations of text occur at different speeds

• request a sample of writing that includes a signature

conclusions drawn from comparisons

• Positive ID = suspect sample matches evidence found which excludes other writers

• Probable ID - combination of similarities, leaves theoretical possibility of another writer

• Unable to determine - not enough writing to make any conclusions

• Positive elimination - samples do not match at all which excludes the writer

account on glass fragment analysis

• fitting together fragments from crime scene from suspect fragments can provide very strong evidence linking suspect to crime BUT most glass is too fragmented to permit this

• chemical composition of glass types is uniform among manufacturers

• refractive index is used for chromatography glass particles - it does not individualize glass to a single source but it can classify the type of glass

• when fragments of comparable densities are found, their refractive indices are determined

• light waves travelling in air, blow and bend upon entering another medium such as glass or water

• refractive index = velocity of light in vacuum/ velocity of light in medium

• Refractive index measurements are carried out under controlled conditions of temperature and light as the RI will vary with these factors

• a wavelength of 589.3nm is normally used this is called sodium D light

• when a transparent solid like glass is immersed in a liquid with a similar RI, light is not refracted and the boundary cannot be seen

• Immersion method - glass particles are immersed in a liquid medium who’s RI is adjusted until it matches the glass particles

• match point is when the disappearance of the Becke line occurs

• RI of the immersion liquid is adjusted by temperature

• automated approach to measure RI of glass is through use of the GRIM instrument - glass refractive index measurements

account on glass fracture analysis

• fractured window glass gives information on the force and direction of impact

• penetration of window glass by bullet or stone produces a fracture pattern where cracks radiate outwards - radial fractures and encircle hole - concentric fractures

• small stone can give similar pattern to a bullet

• larger stone can completely shatter similar to close range gun shot

• direction of impact can be determined by examining the hole on both sides - the exit hole will be larger

• slower the projectile, the more irregular the shape of the hole so it cannot determine the direction of impact

• it is possible to tell sequence of fractures in a pane of glass by observing the fracture lines and their points of termination

• a fracture always terminates at an existing line of fracture

presumptive tests for blood evidence

• KM/Kastle Meyer test where oxygen is liberated from hydrogen peroxide through peroxidase activity of the heme group in hemoglobin

• the reaction goes from colorless to pink if the blood is oxidised

• blood is rubbed with filter paper

• a drop of absolute ethanol is added, a drop of KM solution is added and a drop of hydrogen peroxide is added

• pink color develops which indicates blood is present

confirmative test for blood

• ELISA - enzyme linked immunosorbent assay

• highly sensitive test that can detect human hemoglobin

• sample undergoes a procedure involving specific antigens that bind to hemoglobin, resulting in a color change

presumptive test for semen

• acid phosphate test - AP is an enzyme present in high quantities in semen

• it turns purple in the presence of acidic solution and fast blue B dye

• moistened filter paper pressed on an item and test solutions are added

confirmative test for semen

• PCR - DNA profiles are extracted from semen to confirm its presence and to identify potential male contributors

• DNA is extracted from the sample

• Polymerase chain reaction is sued to amplify male DNA which is then compared

List four methods by which blood evidence is collected

• scrapping, tape lifting, swabbing and cutting

• scrapping - bloodstains can be scrapped into a piece of paper, which is folded and put in an envelope

• tape lifting - sellotape covers the stain and then placed on a sheet of acetate and put in an envelope

• swabbing - swab with a sterile swab dampened with distilled water, used as a last resort as wetting causes degradation of DNA

• cutting - section of carpet with dried blood can be cut out with sterile cutting device

Describe the process of STR analysis, type of DNA regions analyzed, PCR, analysis of PCR products and an electropherogram

• STR = short tandem repeats that have three-five nucleotides as core repeat

• due to small size, PCR can be used to amplify this region

• Genomic DNA is analyzed between 10 and 17 loci

• fragments of DNA containing STR are amplified and labelled with fluorescent dyes in a PCR reaction

• fragments are then analyzed in an automated capillary gel electrophoresis to measure their length and determine which alleles are present

• a computer generated electropherogram showing peaks representing each allele is created from the data

• x-axis is the time taken for DNA to amplify

• y-axis is the amount of fluorescence detected

explain the principle of GC Mass spectrometry analysis and give applications of this technique

• GCMS = gas chromatography mass spectrometry

• separates components of a complex mixture into its components but does not identify them

• coupling GC and MS to overcome this problem

• mixture is first separated on the GC and each component flows directly into the spectrometer as it emerges from the GC

• separates a compound into individual components and then identifies each component

• it is used in drug analysis to identify and quantify drugs in biological samples such as blood, urine and hair

• allows forensic toxicologists to detect the presence of illicit drugs

outline different categories of fibers found from a crime scene

• natural fibers, manufactured fibers - regenerated and synthetic fibers

• natural fibers are derived from animal or plant sources

• includes wool, mohair, cashmere and silk

• identification relies on microscopic examination of color and morphology

• the most prevalent plant fiber is cotton

• regenerated fibers are manufactured from processing of natural raw materials such as cotton or wood pulp such as acetate

• synthetic fibers are made from synthetic chemicals

• made from long chained molecules called polymers which includes nylons, polyesters and acrylics

physical methods to examine fibers

• light Microscopy: Uses visible light to magnify fibers to analyze their morphology, diameter, and surface characteristics. Different types of lighting (e.g., polarized light) can enhance contrast and reveal unique features.

• Scanning Electron Microscopy (SEM): Provides a high-resolution view of the fiber's surface topography and morphology at a much higher magnification than light microscopy.

• Cross-section Analysis:

  • Involves cutting fibers across their length to observe their cross-sectional shapes, which can help identify specific types of fibers.

• Fiber Burn Test:

  • Involves burning fiber samples to observe the burning characteristics (flame color, odor, residue) that can provide information about the fiber type (e.g., natural vs. synthetic).

chemical methods to examine fibers

1. dePyrolysis-Gas Chromatography-Mass Spectrometry (Py-GC-MS):

   • Involves heating a fiber sample to break it down into smaller chemical components, which are then analyzed by gas chromatography and identified by mass spectrometry.

2. Chromatography:

   • Various forms of chromatography, including Thin-Layer Chromatography (TLC) and High-Performance Liquid Chromatography (HPLC), can be used to separate and analyze the dye components of fibers.

describe the process of VNTR DNA profiling and state the limitations when compared to STR profiling

• portions of DNA contain sequences of nucleotides that are repeated

• the number of tandem repeats differ from one person to another

• all humans have the same type of repeats but have a huge variation in the number of repeats at different regions of the genome

• repeats are cut out of the DNA using enzymes called restrictive enzymes

• the cut pieces of DNA are called restriction fragments

• fragments vary in length and therefore referred to as polymorphic

• this DNA typing is called RFLP - restriction fragment length polymorphism

• VNTR loci are larger and have longer repeat units

• STR have shorter repeat units making them easier to amplify using polymerase chain reaction PCR

• VNTR analysis is more complex and time consuming

• STR is analyzed rapidly and is cost effective

• VNTR fragments are prone to degradation

• STR fragments are shorter and are more resistant to degradation

forensic analysis of pain evidence referencing both physical and chemical investigations

• microscopic analysis, GC pyrolysis and FTIR are analytical techniques used to physically compare paint samples

• color more than any property imparts the most distinctive characteristics to paint

• stereomicroscope is used for side by side comparison of color surface texture and color layer sequence

• paints cant be dissolved in the solvent for standard GC

• they are heated/pyrolized to high temperatures (500-1000 degrees) and decomposed into gaseous products

• gaseous products enter the carrier gas stream and flow through the GC column

• chromatogram is called a pyrogram

• FTIR - Fourier transform infrared spectroscopy

• used to obtain an IR spectrum of a solid, liquid or gas

• term originates from the mathematical algorithm known as Fourier transform which is required to convert raw data into actual spectrum

how are crime scenes secured

• crime scene is secured and isolated

• cordoned off using crime scene prevention tape to preserve all areas of the scene

• prevent unauthorized personnel from having access to the scene

• a record is kept of all personnel entering and exiting the scene

how crime scene are recorded

• recorded in its untouched state

• items of physical evidence are photographed where they are found

• dimensions of the crime scene are sketched having been measured

• detailed notes of scene are made - time each item is discovered, who discovered it and how it was packaged

• video recording with narrative used to transcribed into text

how a crime scene is processed with reference to search warrants

• emergency circumstances allow a crime scene to be searched without a search warrant

• to prevent the loss of evidence or life

• if an arrest has been made

• if consent is given my the landlord/property owner

• otherwise search is deemed unlawful and all evidence is inadmissible

how a crime scene is recorded

• record maintained of all who handled, transported and examined evidence

• continuity of possession is established when evidence is presented

• each item handed over is accompanied by signature and receipt

• as few persons as possible should handle the exhibits

• any person handling an exhibit at any stage can be called as a potential witness in court