Forensic Science PDF - Paper 5, Module 1

____________________________________________________________________________________________________ Subject FORENSIC SCIENCE Paper No and Title PAPER : 5, Forensic Chemistry & Explosives Module No and Title MODULE : M1, Forensic chemistry: i...

____________________________________________________________________________________________________ Subject FORENSIC SCIENCE Paper No and Title PAPER : 5, Forensic Chemistry & Explosives Module No and Title MODULE : M1, Forensic chemistry: introduction Module Tag FS_P5_M1 TABLE OF CONTENTS 1. Learning Outcomes 2. Introduction: Forensic Chemistry 3. History 4. Definition 5. Role of a Forensic Chemist 6. Scope and Significance in Forensic Science 7. Techniques Employed in Forensic Chemistry 8. Cases Encountered in Forensic Chemistry 8.1 Arson Investigation 8.2 Gun Shot Residues 8.3 Toxins 8.4 Noxious Chemicals 8.5 Miscellaneous Analysis 9. Summary FORENSIC SCIENCE PAPER No.5: Forensic Chemistry & Explosives MODULE No. 1 : Forensic Chemistry: Introduction ____________________________________________________________________________________________________ 1. Learning Outcomes After studying this module, you shall be able to know · What is Forensic Chemistry? · History and definition of Forensic Chemistry. · About the Role of a Forensic Chemist. · What is its scope and significance in Forensic Science? · Different techniques that are employed in Forensic Chemistry? · Cases that are generally encountered in Forensic Chemistry 2. Introduction : Forensic Chemistry Forensic Science in its broadest sense is the application of techniques and principles of science for the purpose of administration of criminal justice system. Chemistry is an integral part of forensic science. Forensic scientists must understand the principles, concepts and techniques of chemistry to perform their duties in an effective manner. Scientists of all types are often interested in the composition of a substance. However, the type of substance may vary according to their nature of work. Like, pharmaceutical scientists identify the substances in a drug sample to set their expiry dates. Similarly forensic scientists identify substance to connect suspects to crimes or to reconstruct a crime i.e. to determine how a crime has been committed. This area of science is generally considered very fascinating and it continues to experience increasing popularity. The current trend of public interest in forensics is a direct result of various popular investigating programs on television. Crime investigation T.V. shows (particularly C.I.D. in India), movies and various games on internet have brought forensic science into the spotlight. Many of the tests they show technicians performing, involve chemistry. Like, they use a substance to detect the presence of blood stains which otherwise could go unnoticed. That substance turns those spots into luminous stains. That magical looking substance is actually “Luminol” which reacts with blood to form a compound that glows when illuminated under UV radiation. In addition the stories often show crime scene specialists bringing samples back to laboratory for examination in any one of the several large machines that seems to print out a report in just a few seconds. But in reality it is much more complicated than that. Chemists can analyze a substance in various ways in order to determine its composition. After determining the composition of the substance, they can compare it to already analyzed samples. If they find a match between the sample obtained from the crime scene and the known sample often called “Control Sample”, they can identify the origin of the test sample collected from the crime scene. Not only these television shows but the media has also contributed a lot in the development of Forensic Science. The coverage of different criminal cases has brought the crime scene investigation and forensic analysis out of the labs among public. FORENSIC SCIENCE PAPER No.5: Forensic Chemistry & Explosives MODULE No. 1 : Forensic Chemistry: Introduction ____________________________________________________________________________________________________ 3. History The very first history of Forensic Chemistry began with analysis of poisons. In early times, there are evidences of the use of poisons by early Egyptians, Greeks and Romans. At that time, poisons were used both for murder and for the execution of death penalty; the philosopher Socrates was sentenced to death by drinking hemlock. Before the development of any systematic scientific procedure of criminal investigation, circumstantial and hearsay evidences were usually employed to ascertain the guilt of any person. Arsenic was a commonly used poison during Roman times. The first instance of an actual chemical test for poison is the Blandy trial conducted during 1752. 4. Definition Chemistry is the branch of science that deals with the study of the composition of matter and different changes that it undergoes. Forensic chemistry is a specialized sub-field of forensic science involving the application of techniques and principles of chemistry to the field of forensic investigation. It involves complex procedures of chemical analysis that are used to identify elements and compounds. Identification procedures are highly reliable and are frequently based on the physical and chemical properties of the substance supported by the data obtained from analytical analysis. Forensic chemistry is the application of principles of chemistry to law enforcement and criminal justice system. There are various analytical methods which may be used to find out the chemical changes that occurred during any incident, and in this way it helps in the reconstruction of crime scene. Forensic chemistry meets the need of both the scientific and the legal communities by innovations in its research, practice, and presentation. Every facet of the criminal justice system would suffer without forensic chemistry. Forensic chemistry acts as armed force in the pursuit of justice. Forensic chemistry gives voice to the silent witness of physical evidence. It plays a critical role in the administration of justice, not only aids in the investigation and prosecution of crimes but also assist in meeting up the ends of justice. 5. Role of a Forensic Chemist The ability of forensic professionals to establish the presence of a link between accused and crime by matching physical evidence collected from the scene of crime and those which are obtained from the victim or accused(Law of Comparison), strengthen the case of prosecution. FORENSIC SCIENCE PAPER No.5: Forensic Chemistry & Explosives MODULE No. 1 : Forensic Chemistry: Introduction ____________________________________________________________________________________________________ Forensic chemists perform different analyses to identify materials in order to determine the nature and composition of such evidence. A highly trained forensic chemist is capable of determining the composition and nature of materials and predicting the source as well as matching evidences collected from the crime scene with the control sample. Modern chemistry employs the traditional analytical techniques hand in hand with much younger methods of analysis. Physical evidence collected from the scene of crime is properly collected, packaged and sealed in special containers to order to maintain its integrity and to prevent contamination. A chain of custody should be maintained for each evidence which is sent to forensic laboratory for examination. At the laboratory, the evidence is examined by trained personnel to reach up to a definite opinion. Forensic chemists have a crucial role in forensic science laboratories and when required they are often called on in the courts, to provide testimony as expert witnesses. In these cases, the chemist may compare questioned evidence to control samples and may be asked to give an expert opinion in court on the basis of grounds on which such opinion is based. Their academic credentials, along with years of experience to deal with such analysis, render their opinion valuable and believable. The fact that most samples that are submitted for analysis are contaminated with dirt or debris and several other contaminants, this poses a major challenge before forensic chemist. Every substance that is collected from the scene of crime has a unique composition that can ultimately be identified. Arsonists, for example, often use accelerants such as kerosene or gasoline to accelerate the rate of combustion and each accelerant has its own unique composition. A forensic chemist may search for and collect burnt and unburnt material samples, extract the volatile hydrocarbons from them, and may use gas chromatography to separate the components of these samples. Forensic chemists closely examine criminal evidence. 6. Scope and Significance in Forensic Science The principles of chemistry play quite a crucial role in each division of Forensic Science Laboratory. A few of them are as follows- FORENSIC SCIENCE PAPER No.5: Forensic Chemistry & Explosives MODULE No. 1 : Forensic Chemistry: Introduction ____________________________________________________________________________________________________ a) Examination of metal alloys and metal fragments for identification and comparison. b) Examination of petroleum products like diesel, petrol, and kerosene. c) Analysis of dyes, paints, inks, fillers, binders and various other chemicals to their identity, composition, quality as well as quantity. d) Examination of low standard construction material like cement, bricks, etc. as well as the adulteration in these building materials. e) Analysis of various narcotic, designer and abused drugs like bhang, opium, ganja, LSD etc. as well as illicit liquors. f) Determination of alcohol in blood and urine in cases of suspected drunkenness and analysis of fermented wash, varnish, etc. in prohibition and excise cases. g) Analysis of pesticides for their identification. h) Examination of inflammable material in suspected cases of arson, dowry deaths, etc. i) Analysis of explosives, firearms and ammunition. 7. Techniques Commonly Employed in Forensic Chemistry Forensic chemistry deals with both organic and inorganic analysis. Each method of analysis is coupled with specialized techniques and instrumentation. The process may range from simple ones like conducting a chemical test or comparing the density of evidences like soil samples; to the complicated ones like using a neutron activation analysis or mass spectrometer to characterize an unknown substance. A vast range of analytical techniques are generally employed in forensic analyses. This includes ultraviolet, visible and infrared, spectrophotometry; GCMS; high pressure liquid chromatography; neutron activation analysis; and atomic absorption spectrophotometry. The choice of technique and instrument to be used depends on the type of sample to be analyzed. 8. Cases Encountered in Forensic Chemistry Forensic Chemistry deals with the chemical analysis of a variety of physical evidences. These include samples of suspected accelerants from noxious chemicals, arson debris, propellants, lubricants, gunshot residues, etc. The cases that are typically examined include, homicides, arsons, assaults, robberies, etc. A few of them have been discussed below: 8.1 Arson Investigation Arsonists may use a number of accelerants to set a fire. During the examination of any arson scene and its background cause, investigators must look for the fire debris that they believe to contain residues of the accelerants used in arson. The debris is collected and packed in airtight containers to avoid loss of its volatile components and is then transported to Forensic Science Laboratory for analysis. Gas Chromatography-Mass Spectrometry is employed to identify and quantitatively analyze the traces of ignitable liquid residue in collected samples. Along with this, FORENSIC SCIENCE PAPER No.5: Forensic Chemistry & Explosives MODULE No. 1 : Forensic Chemistry: Introduction ____________________________________________________________________________________________________ the forensic chemists often concentrate on several other minute residue traces. They do this by using activated charcoal strips to adsorb the accelerant residues which are then eluted off the strip by dissolving in a solvent. 8.2 Gun Shot Residue In addition to arson debris, this section also analyzes evidences associated with shooting cases. When ammunition is discharged from a weapon, gases are generated which contain burned and unburned components of primer and propellant cartridge which may deposit on the hands and cloths of the person firing the weapon and is referred to as Gun Shot Residue (GSR). Scanning Electron Microscope (SEM) coupled with an Energy Dispersive Spectrometer (EDS) is used to examine tape lifts taken from the hands of suspected shooters. If elements like barium, antimony, and lead is found in the sample, it is classified as primer residue. 8.3 Toxins Forensic chemists examine a vast range of evidences such as blood stains, urine, etc for traces of drugs or poisons. Many businesses including sports now require the drug screening of employees and sports persons; it is the chief task of the forensic chemist to distinguish between the external addition of illegal drugs and metabolites from certain food materials like poppy seeds. Such tests may be as simple as various color tests or may involve different instrumental techniques ranging from simple to complex one. Paper or thin-layer chromatography or complicated techniques like gas chromatographic or electrophoresis could be used for the analysis of different toxins. In death cases due to unknown cause, samples of the victim's blood, lungs, urine, stomach content and vitreous humor are examined for traces of poisons. Insects, in some cases, found on the dead bodies are also examined; as they may absorb drugs or poisons from the body in trace amounts, which sometimes are found long after, even when the concentrations in the body have fallen down. 8.4 Noxious Chemicals Noxious chemicals like capsaicin spray and tear gas can be both qualitatively as well as quantitatively analyzed by using the Gas Chromatograph-Mass Spectrometer (GC-MS). Tear gas is a component in dye packs that are used by banks to identify the suspects as they may be found on the clothing of the person involved, after the dye pack has exploded. 8.5 Miscellaneous Analyses The Forensic Chemistry can also assist in investigation of sexual assault cases by examining the lubricants (even when present in traces) used by suspects in rape cases. FORENSIC SCIENCE PAPER No.5: Forensic Chemistry & Explosives MODULE No. 1 : Forensic Chemistry: Introduction ____________________________________________________________________________________________________ 9. Summary · Chemistry is an integral part of forensic science. Forensic scientists must understand the principles, concepts and techniques of chemistry to perform their duties in an effective manner. · The very first history of Forensic Chemistry began with analysis of poisons. · Forensic chemistry is the application of principles of chemistry to law enforcement and criminal justice system. · Forensic chemists analyses the materials to determine their nature and establishing a link between crime, criminal and victim. · Forensic chemistry has vast applications including analysis of dyes, paints, inks, fillers, binders and various other chemicals to their identity, composition, quality as well as quantity. · Forensic chemistry incorporates both organic and inorganic analysis. Each method of analysis uses specialized techniques and instrumentation. FORENSIC SCIENCE PAPER No.5: Forensic Chemistry & Explosives MODULE No. 1 : Forensic Chemistry: Introduction