Forensic Science Notes PDF

CM5002 FORENSIC SCIENCE TOPIC 1: INTRODUCTION Objectives: Explain the origins of forensic science and some basic concepts, Explain how forensic science fits into the criminal justice system, Understand individualisation, reconstruction and reenactment, Describe different kinds of forensic labs, Exp...

CM5002 FORENSIC SCIENCE TOPIC 1: INTRODUCTION Objectives: Explain the origins of forensic science and some basic concepts, Explain how forensic science fits into the criminal justice system, Understand individualisation, reconstruction and reenactment, Describe different kinds of forensic labs, Explain Locard’s Exchange Principle What is Forensic Science 1. Application of Science to Law 2. Application of Science to Criminal justice: the analysis of physical, chemical and biological evidence Differences between Forensic Medicine and Forensic Science Forensic Medicine Analysis the body Injury, cause of death / time of death Forensic Science DNA, Drugs, Ballistics (examining the evidence from firearms), documents, fibres, fingerprinting, physical evidence Saliva and blood group are not relatable Forensic Science in court Evidence from: Prosecution Judge (VERDICT FORM) vs 1. Experts Vs Jury - Selected from amongst 2. Witnesses local citizens (abolished in 3. Police Defence some countries like SG) Presumption of Innocence “The burden of proof is on the one who declares, not on one who denies” Innocent until proven guilty BEYOND reasonable doubt The limits of Forensic Science 1. Actus Reus A guilty action 2. Mens Rea A guilty mind or intention MUST HAVE BOTH IN ORDER TO BE CONSIDERED AS MURDER Eg when a person did a guilty act (actus reus) but got SCAMMED (not mens rea) → HENCE IT IS NOT A MURDER “Actus non facit reum nisi mens sit rea” (the act does not make a person guilty unless the mind is also guilty) Reconstruction - Comparison - Association FS enable use to reconstruct the past sequence of events Reconstruction ○ Understanding the sequence of past events Reenactment ○ May be a part of reconstruction Can link a suspect to a crime scene Will have to ask if it’s suicide or murder FS will have to compare the evidence with the criminal / suspects The Locard Exchange Principle EVERY CONTACT LEAVES A TRACE Forensic Science Laboratories 1. Physical Science Unit: Identification and comparison of evidence, chemical tests, spectroscopy, microscopy, drugs, glass, paint, explosives, soil 2. Biology Unit: Hair, plants 3. DNA Lab: DNA 4. Firearms Unit: Guns, bullets, cartridge cases, firearm damage 5. Documents Unit: Handwriting, printing, paper, ink 6. Photography Unit: Record of evidence, presentation 7. Toxicology Drugs and poisons in body fluids and organs 8. Latent Fingerprints Making them visible Not all fingerprints are visible to the naked eye – chemical means to make them show up 9. Polygraph or lie detector Can we scientifically detect a lie? Jurdy do not accept evidence from lie detector 10. Voiceprint Analysis of voices 11. Psychiatric profiling What can we tell about the criminal from the way they commit the crime? 12. Computer Forensics and Electronic Forensics What can be learned from deleted data? How can other electronic trails be followed? Data can be restored even if it is deleted 13. Forensic Engineering Why did the I35 bridge in Minneapolis collapse? The Morandi Bridge in Genoa? 14. Forensic Entomology Using insects to provide information 15. Forensic Geology Soil analysis: mineral content and chemistry 16. Forensic Anthropology Examination of skeletal remains 17. Facial Reconstruction If you have the skull, can you tell what the face looked like? Take skulls and rebuild the tissues  Sometime may not work well 18. Forensic Odontology Using teeth to provide information: identification of victims remains or identification of a criminal Individualisation MULTIPLE EVIDENCE TGT – > TO MAKE A PERSON GUILTY The Locard Exchange Principle EVERY CONTACT LEAVES A TRACE TOPIC 2: SPECTROCOPY AND STRUCTURE OF ATOMS Objectives: Explain the concept of chemical elements, From an understanding of atomic structure explain how emission and absorption spectroscopy work, Flame tests, AAS, SEM-EDX, NAA Atomic spectroscopy: how the analysis of the elemental composition of a sample can yield information. Molecular spectroscopy: determination of the compounds present in a sample by chromatographic and spectroscopic means Elements and Compounds Element are the basic materials Element can neither be created or destroyed Those that have filling in teeth → gold and mercury can be found in their teeth What is it made of 1. Bulk composition (what is it mostly made up of) 2. Trace of impurities Chemical tests Large amounts Destructive Subject to interference Fast Easy to do Simple equipment How small is small Trace elements are often measured in ppm = part per million 1 in 1,000,000 Spectroscopy Fraunhofer lines are found due to hydrogen Different spectroscopic techniques use different frequencies of light The different frequencies of light interact differently with the molecules Why don’t atoms destroy themselves due to electrostatic attraction Electrons are restricted to specific energy levels Atomic structure From excited state to ground state → Energy is released as electromagnetic radiation The frequency of the electromagnetic radiation emitted or absorbed is proportional to E (the energy drop) De Broglie eqn: E = hv From ground state to excited state → Energy is absorbed as electromagnetic radiation Energy Levels May not be that good as atom energy level are not evenly spaces The pattern is characteristic for each element Energy is taken in → to add energy to the atom to promote to its excited state Emission spectrum Using a spectrum of the element can be obtained Flame tests for metal - To find out which element is present What it does: ○ Introducing a sample of the element or compound to a hot, non-luminous flame and observing the colour of the flame that results Colour → identity Intensity → quantity If a metal salt is introduced into the flame → CHARACTERISTICS colour is produce How it works: ○ Put the metal over the flame ○ Energy of the flame excites electrons in the sodium atoms ○ Emit orange light as they drop back to the ground state Atomic Absorption Spectrometer (AAS) What is does: ○ Detects elements in either liquid or solid samples through the application of characteristic wavelengths of electromagnetic radiation from a light source Loss of intensity is related to amount of the atom of interest in the flame because the atoms in the flame absorb Advantages: 1. Fast 2. Specific 3. Sensitive 4. Small sample size Disadvantages: 1. Destructive ➔ Need to be in a solution form 2. Element by element ➔ Due to different light intensity Energy Dispersive X-ray Fluorescence (EDX) Non destructive analysis looking at the core electrons Use an electron beam to eject core electrons Microscopy What is does: ○ Technical field of using microscopes to view samples & objects that cannot be seen with the unaided eye ○ For eg the participle of gunshot residue Scanning Electron Microscope (SEM) that produces images of a sample by scanning the surface with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that contain information about the surface topography and composition of the sample Neutron Activation Analysis (NAA) What is does: ○ An analytical technique that relies on the measurement of gamma rays emitted from a sample that was irradiated by neutrons Non - destructive but needs a nuclear reactor sample may be radioactive afterwards 70% of the element can be studied Qualitative and Quantitative multi-element analysis You are what you eat True: You eat what is grown locally False: For advance society → you eat what is imported Calcium is derived from the diet Relative abundance of trace elements in bone can indicate geographical origin: strontium, copper, lead Elemental Analysis 1. Spectroscopic methods Flame Photometry Absorption (AAS) 2. X-Ray 3. Microscope 4. NAA TOPIC 3: TIME OF DEATH Objectives: How this can be determined by chemical, biological and circumstantial means, minutes to centuries, Appreciate the inherent uncertainty Time of death 1. Temperature Algor Mortis: ○ After death muscles relax, body limp starts to cool Different parts cool at different rates (brain cool faster than liver) Start to warm up after two days (putrefaction - process of decay) Temperature of the surrounding can be higher or lower than the temperature Various factor could affect the rate of temperature change Newton’s Law of cooling: ○ Rate is proportional to the temperature difference 2. Stiffness Rigour Mortis: ○ Lactic acid in muscle causes tension ○ up to 36 hours after death Jaw (2 hrs) Arms (4-6 hrs) Legs (8-10 hrs) Whole body (10-12 hrs) 3. Colour of the body Livor Mortis: ○ Settling of red blood cells due to gravity ○ Takes 0-12h Discolouration in the lower parts ○ Could see if the body has been moved CO poisoning – cherry pink due to the carbon monoxide-haemoglobin complex  4. Other indicator K+ levels in the ocular fluid (vitreous humour) increases after death Stomach and Intestine contents (time of last meal) ○ Stomach empties in about 2 hours Electronic devices ○ Mobile phone and CCTV Putrefaction Process of decay or rotting in body After death, microorganism start to eat you Timeline 2-3 days: staining begins on the abdomen. Body begins to swell due to gas formation. 3-4 days: staining spreads. Veins become discoloured 5-6 days: abdomen swells with gas. Skin blisters 2 weeks: abdomen very tight and swollen. 3 weeks: tissue softens. Organs and cavities bursting. Nails fall off. 4 weeks: soft tissues begin to liquefy. Face becoming unrecognisable. Mummification Method of treating the dead body → the dead body is kept Body is preserved cleaning in dried form → body will not decay easily Forensic Entomology Uses insects found on corpses to help solve criminal cases USUALLY IS A RANGE How it works: ○ Insects can arrive and lay eggs soon after death ○ Have to know: Species, life cycle, local conditions Collect live maggots from the corpse and rear until adulthood Then back calculate age and determine species Disadvantage ○ The result may not be accurate due to Weather Microclimates Covering of the body Case study ○ Peter Thomas 1964 Covered by maggots Police assume the death timing from the life cycle The Jury believes maggots and not the eye-witnesses ○ Danielle van Dam 2002 Skeletal remains NO SKELETAL remains → 100 years old or more Piltdown Man ○ Piltdown man (England) discovered 1912-15 ○ Claimed: 500,000 years old ○ In the skull → small amounts of F (0.2%) ○ In the jaw → little or no F nearly 4% nitrogen Bone nitrogen content fresh bone = 4% by weight decreases with age (proteins breakdown) → from here can see how long FUN Analysis has the body be buried for Bone fluorine and uranium content of fresh bone = 0% increases with age (from groundwater) useful only for comparing samples from the same site because F and U in ground water/ minerals is variable → from here can see how long has the body be buried for Carbon-14 dating Is a radioactive isotope Living things have this proportion of 14C Decay at a predictable rate One half of 14C atoms will have decayed in 5568 years (the half life) Why is it imp: Measure the amount of 14C and calculate the time of death Limitation: Not very accurate for