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Transcript
Introduction to Forensic Science A Short Guide for the Perplexed The CSI Effect The CSI Effect The CSI Effect Juries expect the kind of forensic science shown on CSI Unfortunately, 40% of the forensic science shown on CSI does not exist Before CSI Before CSI Before CSI Before CSI What is Forensic Science? Forensic science is the application of scientific principles to the resolution of legal issues – in criminal, civil and administrative hearings Forensic Science Specialties Criminalistics Firearms and tool mark examination Document examination Fingerprint identification Forensic photography and image analysis Computer forensics Forensic Science Specialties Forensic pathology Forensic odontology (forensic dentistry) Forensic anthropology Forensic toxicology Forensic psychiatry Forensic psychology (includes criminal profiling) Criminalistics Drug chemistry Trace evidence analysis – – – – Hairs and fibers Glass and soil Paint and plastics Ignitable liquids (arson accelerants) – Explosive residues – Gunshot residues Forensic biology Forensic molecular biology (i.e. DNA profiling) Types of Evidence Testimonial Documentary Demonstrative Physical Uses of Physical Evidence To prove elements of the crime To identify the perpetrator To reconstruct the crime To confirm or refute the statements of – Complainants – Witnesses – Suspects Types of Physical Evidence Pattern evidence Trace evidence Pattern Evidence Fingerprints Foot impressions Footwear impressions Tire impressions Striation patterns on bullets, breechblock markings, tool marks Powder and shotgun pellet patterns Char and soot patterns Handwriting/typewriting Bloodstain (and other body fluid) patterns Amido Black Crowle’s Stain Hungarian Red Coomassie Blue Fluorescence of Hungarian Red (under green light) What is Trace Evidence? ‘Trace evidence’ refers to the minute bits of physical evidence that may be exchanged among the perpetrator of a crime, the victim and the crime scene The Locard Exchange Principle The Locard Exchange Principle states that when two surfaces come into contact, an exchange of trace evidence takes place across the interface between them ‘Every touch leaves a trace.’ Types of Trace Evidence Solid aggregates – Fibrous (hairs, fibers, botanical samples) – Particulate (glass, soil, metal fragments, paint chips and smears, explosive residues, gunshot residues) Liquids – Blood, semen and other body fluids Molecular traces – Explosive residues, ignitable liquid residues Forensic Analysis of Particulate Trace Evidence Microscopic examination Instrumental methods of analysis as appropriate Infrared Microscopy Combined with FourierTransform Infrared Spectrometry Infrared Spectra of Artificial Hair Strands The Jeffrey McDonald Case Forensic Biology and Forensic Molecular Biology Body Fluids Examined in the Forensic Science Laboratory Blood Semen Saliva Urine Feces Perspiration Screening Suspected Bloodstains Is that red-brown stain a bloodstain? If it isn’t blood we don’t want to include it in our blood spatter analysis If it isn’t blood we don’t want the forensic biologist to waste time processing it as blood evidence Forensic Analysis of Suspected Bloodstains Presumptive tests Confirmatory tests Species identification tests DNA profiling Human Erythrocytes Commercial Blood Test Kits Peroxtesmo Hemastix Luminol Luminol Confirmatory Tests for Blood Takayama test – A crystal test for hemoglobin – Pink, leaf-like birefringent crystals are formed Microspectroscopy – Identifies the characteristic absorption spectrum of hemoglobin Takayama Crystals Takayama Crystals Human Blood Identification Hexagon OBTI Test kits are available for the identification of human blood at crime scenes These are based on the reaction of human hemoglobin with anti-human hemoglobin antibodies DNA Profiling Structure of DNA DNA (deoxyribonucleic acid) is composed of three components – Phosphate groups – Sugars (deoxyribose) – Bases » Adenine (A) » Thymine (T) » Guanine (G) » Cytosine (C) Double-Stranded (Duplex) DNA Mutations The genetic information in DNA can be changed by mutations – Point mutations (one base substitutes for another) – Insertions – Deletions Natural selection constrains the variability of functional DNA (i.e. genes) ‘Non-functional’ DNA has greater variability DNA Extraction Remove cellular material (cell membranes, proteins etc.) Dissociate nuclear DNA from histones Purify DNA Types of Samples Body fluids – Blood Tissues – Muscle – Bone – Teeth Body fluid stains – – – – Bloodstains Semen stains Saliva stains Urine stains PCR – The Molecular Xerox Machine Polymerase chain reaction (PCR) is used to make copies of DNA strands To aid judges and juries in understanding what PCR does many experts compare PCR to using a Xerox copier to make very many copies of the page of a book. A more accurate analogy is using a Xerox copier to make many copies of a sentence on a page in a book. The CODIS System CODIS = Combined DNA Index System CODIS began as a pilot project in 1990 serving 14 state and local laboratories. The DNA Identification Act of 1994 (Public Law 103 322) formalized the FBI's authority to establish a national DNA index for law enforcement purposes. In October 1998 the FBI's National DNA Index System (NDIS) became operational. CODIS is divided into two indices: the forensic index and the offender index The CODIS Core Loci The FBI has identified 13 short-tandem repeat (STR) loci as core loci for the CODIS system If a known sample of DNA matches the questioned sample at all 13 loci the DNA expert can state that both DNA samples came from the same source ABI PRISM® 310 Genetic Analyzer Nuclear DNA STR data DNA Databases Cases Aided by CODIS DNA Databases CODIS (Combined DNA Index System) – NDIS (National DNA Index System) has 4,398,639 DNA profiles » Total Forensic profiles: 167,103 » Total Convicted Offender profiles: 4,231,536 The UK’s ten locus STR database uses eight of the thirteen loci used in the CODIS database DNA Sequencing The actual sequence of As, Ts, Gs and Cs is the ultimate genetic information The Human Genome Project has sequenced the entire human genome Mitochondrial DNA Sequencing Mitochondria contain loops of DNA Each mitochondrion contains several loops of DNA Each cell contains a number of mitochondria Mitochondrial DNA (mtDNA) is maternally inherited Mitochondrial DNA Sequencing Mitochondrial DNA Sequencing In human mtDNA the D-loop (or control region) contains two hypervariable regions (HV-1 and HV-2) The hypervariable regions can be sequenced using appropriate primers Mitochondrial DNA sequence data Advantages and Disadvantages of MtDNA Sequencing There are more copies of mtDNA than nuclear DNA MtDNA can be recovered and sequenced from difficult samples – Degraded samples – Samples lacking significant intact DNA (hair) Due to size of mtDNA database frequency estimates are not possible DNA Profiling and the War on Terror Identification of victims (e.g. World Trade Center) DNA profiles from improvised explosive devices (IEDs) Microbial forensic database My Background Education – BS in Chemistry (Emory University) – AM (1968), PhD (1976) in Chemistry (Harvard University) Forensic Science Experience – 1969-1971 Forensic chemistry specialist, US Army Criminal Investigation Laboratories (drug chemistry and forensic serology) – US Army CID investigator Major Cases The Jeffrey McDonald Case The death of Dale Earnhart The exhumation of Jesse James Forensic Science at The George Washington University We offer the Master of Forensic Science degree Students may specialize in – – – – – Crime Scene Investigation Forensic Chemistry Forensic Molecular Biology Forensic Toxicology High Technology Crime Investigation – Security Management