What is Forensic Science INTRODUCTION TO FORENSIC SCIENCE 10/04/2014. It is the application of Science to Criminal and Civil Laws

Transcription

1 INTRODUCTION TO FORENSIC SCIENCE N. Zeynep Atay Department of Chemistry What is Forensic Science It is the application of Science to Criminal and Civil Laws HISTORY OF FORENSIC SCIENCE 1

2 CRIME SCENE Forensic Science begins at the crime scene. Finished-sketch diagram of a crime scene. Courtesy Sirchie Finger Print Laboratories, Inc., Youngsville, N.C., Criminalistics by Richard Saferstein Prentice Hall 2

3 SERVICES OF THE CRIME LABORATORY MODERN CRIME LABORATORIES CRIME LABORATORIES AND THEIR ORGANIZATION Physical Science Unit Biology Unit Firearms Unit Document Examination Unit Photography Unit OPTIONAL SERVICES PROVIDED BY FULL- SERVICE CRIME LABORATORIES Toxicology Unit Fingerprint Unit Polygraph Unit Lie-detector Voiceprint Analysis Unit Crime-Scene Investigation (CSI) Unit FUNCTIONS OF THE FORENSIC SCIENTIST Analysis of physical evidence Expert Witness Training of staff in the proper recognition, collection, and preservation of physical evidence 3

4 OTHER FORENSIC SCIENCE SERVICES Forensic Pathology Forensic Anthropology Forensic Psychiatry Forensic Odontology Forensic Engineering Forensic Computer and Digital Analysis Forensic Pathology Involves the investigation of sudden, unnatural, unexplained or violent deaths by either observation or through an autopsy. By investigating the stages of decomposition of the body, time of death can be estimated. Forensic Anthropology Forensic Entomology Involves mainly the identification and examination of human skeletal remains. Study of insects and their relationship to criminal investigation. Examination of bones may reveal sex, approximate age, race and skeletal injury. Especially helpful identifying victims of a mass disaster, such as a plane crash, through the collection of bone fragments. After decomposition begins, insects such as blowflies start infesting the body, laying their eggs in human remains, and ultimately hatch into maggots, etc. Entomologists can identify these insects and approximate how long the body has been left exposed by examining the stages of fly larvae. 4

5 Forensic Psychiatry A specialised area which investigates the human behaviour and legal proceedings. For civil cases, they determine whether the person is competent to make decisions on wills, etc. For criminal cases, they evaluate behavioral disordersand determine competence to stand trial. Criminalistics by Richard Saferstein Prentice Hall Forensic Odontology Forensic Engineering Helps identify victims through dental remains when the body is in unrecognizable state. Teeth are composed of enamel, the hardest substance in the body. Due to the resilience of enamel, the teeth outlasts tissues and organs as decomposition begins. Dental records can be compared to the suspected victim. Bite-mark analysis is also important in identifying the suspect. Accident scenes are examined, photographs are reviewed, mechanical objects are investigated. How did an accident or failure happen? Were the parties involved responsible? If yes, how were they responsible? 5

6 Forensic Computer and Digital Analysis A new and fast growing field that involves identification, collection, preservation and examination of information derived from computers and other digital devices such as mobile phones. PHYSICAL EVIDENCE Physical Evidence can provide a link between a crime and its victim or a crime and its perpetrator Common Types of Physical Evidence Fingerprints (a classic identifier) Blood, Semen and Saliva these are subject to serological and biochemical analysis (all contain DNA) Documents any handwriting, typewriting, ink, indented writing, obliterations, burned or charred documents (letters and s link people) Explosives any device with an explosive charge and any item that might contain the explosive residue A fingerprint exhibit illustrating the matching ridge characteristics between the crime-scene print and an inked impression of one of the suspect s fingers. Courtesy New Jersey State Police. Criminalistics by Richard Saferstein Prentice Hall 6

7 Friction Ridges Every person has minute raised ridges of skin on the inside surfaces of their hands and fingers and on the bottom surfaces of their feet and toes, known as 'friction ridge skin'. The friction ridges provide a gripping surface - in much the same way that the tread pattern of a car tyre does. Friction ridge skin is also the only skin on the body without hairs. Fingerprint ridge characteristics. (Courtesy Sirchie Finger Print Laboratories, Inc., Youngsville, N.C., Fingerprint Ridge Characteristics 150 different ridge characteristics = minutiae (trivial details) How many fingerprint points must match in order for the fingerprints to be said to be identical? UK 16 pts. New Zealand and Australia 12 pts. India 8 pts. USA each state has its own standard FBI uses 12 pts. There is really no scientific basis on how many points should be matched!!!! 7

8 The Principles of Fingerprint Identification Uniqueness: No two friction ridge patterns are identical, whether they are on different fingers of the same person or on the fingers of different people. (The same principle covers all friction ridge skin.) While this principle is difficult to prove empirically, no two fingerprints have ever been found to be identical in over a century of the use of fingerprinting. Friction ridge patterns do not change naturally during the life of a person. The pattern of minutiae starts developing in the third month of pregnancy and is fully formed by the fourth month. During a person's lifetime, the pattern remains the same, apart from changing in size or by accident, mutilation or skin disease, until death. In fact, the friction ridge patterns will remain after death until the body decomposes. POWDERS Powder And Tape Probably the most well-known method of detecting latent prints is dusting for them. A variety of powders are used in dusting for prints, many containing aluminium or carbon. This finely crushed powder is gently applied to a surface, and the minute particles of powder cling to the print residue, making it visible to the human eye. These prints are then lifted using adhesive tape. Additionally, studies have demonstrated that while identical twins share the same DNA profile markers, they can nevertheless be differentiated by their fingerprints. Drugs Brush it with aluminum powder The marks became visible. Put a black rubber lifter on it. Marijuana The marks are on the lifter. Put a plastic sheet over it. Ready to search! 8

9 Fibers any fiber that might show crosstransfer between object and/or persons (can link suspect and crime scene) Ice-methamphetamine 9

10 Hair animal or human hair showing cross-transfer (hair can be matched microscopically) DOG HAIR In humans, pigment granules are commonly distributed toward the cuticle as shown in top figure, except in redhaired individuals as in bottom figure. Animal hairs have the pigment granules commonly distributed toward the medulla, as shown in the figure. Forensic Science CommunicationsJuly 2004 Volume 6 Number 3 CAT HAIR Forensic Science CommunicationsJuly 2004 Volume 6 Number 3 Photomicrograph of Human Hair Root Wineglass-shaped root (deer family) The root of human hairs is commonly club-shaped, whereas the roots of animal hairs are highly variable between animals. Forensic Science CommunicationsJuly 2004 Volume 6 Number 3 Forensic Science CommunicationsJuly 2004 Volume 6 Number 3 10

11 UNLESS DNA analyses are carried out: Body area from which the hair originated: Scalp hair: little variation in diameter Uniform pigment distribution Might be dyed Pubic hair: Short and curly Variable cross-section diameter Continuous medullae Beard hair: Coarse Triangular cross-section Blunt (not sharp) tips from shaving and cutting Class Evidence: Hair UNLESS DNA analyses are carried out: Age: Age of an individual cannot be learned with any certainty except for infant (baby) hair. Infant hair: Short Undeveloped in character Sex: Hair gives no indication of the sex of the individual from which it came. Glass Common Types of Physical Evidence (continued) Particles that may show cross-transfer or panes that might have bullet holes (fragments are easy to compare) Two bullet holes in a piece of glass. The left hole preceded the right hole Firearms and Ammunition discharged or intact Impressions tire markings, shoe prints, depression in soil, glove or fabric impressions, bite marks in skin or food, as well as knife cuts Criminalistics by Richard Saferstein Prentice Hall 11

12 Purpose of the Examination of Physical Evidence Identification: Identification: Determination of the physical or chemical identity of a substance with as near absolute certainty as existing analytical techniques will allow. Comparison: Subjecting a suspect specimen and a control specimen top the same tests for the ultimate purpose of proving common origin. (Comparing two or more samples to see they match.) Typical tests for identification: Drug analysis Species determination Explosive residue analysis Drugs: Testing the composition of a white powder may show that it is illicit or prescription drug. Scientists need to determine what type of drug it is: heroin, cocain or barbiturates, or a commonly used drug! Fibers: In case of suspected arson, fragments of cloth, found where the fire officers believe the fire might have started, could have petrol residues lingering in the fabric. Comparison: Characteristics of Physical Evidence If any of the selected properties are not alike, the scientist will declare that the two items are not from the same source. However, if all the selected properties match, they still may not be able to conclude that the two specimens are from the same source with 100% accuracary. Hence, usually only the probability that two specimens came from the same source is given. Individual: Associated with a single source with extremely high probability Examples: Fingerprints Bullet Striations Footprints DNA Class: Associated with a class with high probability, but associated with a single source with low probability. Information can be gained by looking at the class of an item. Example: Hair Blood type (O, A, B, AB) 12

13 Class Evidence: Hair Body area from which the hair originated: Scalp hair: little variation in diameter Uniform pigment distribution Might be dyed Pubic hair: Short and curly Variable cross-section diameter Continuous medullae Beard hair: Coarse Triangular cross-section Blunt (not sharp) tips from shaving and cutting Class Evidence: Hair Age: Age of an individual cannot be learned with any certainty except for infant (baby) hair. Infant hair: Sex: Short Undeveloped in character Hair gives no indication of the sex of the individual from which it came. Sources of Biological Evidence The probability of 2 people having the same fingerprint is 1 in 1x10 60 Blood Semen Saliva Urine Hair Teeth Bone Tissue 13

14 DNA Use in Forensic Cases Most are rape cases (>2 out of 3) Looking for match between evidence and suspect Must compare victim s DNA profile Challenges Mixtures must be resolved DNA is often degraded Inhibitors to PCR are often present Human Identity Testing Forensic cases -- matching suspect with evidence Paternity testing -- identifying father Historical investigations Missing persons investigations Mass disasters -- putting pieces back together Convicted criminal DNA databases CODIS CODIS (Combined DNA Index System) is a computer software program developed by the FBI that maintains local, state, and national databases of DNA profiles from convicted offenders, unsolved crime scene evidence, and profiles of missing persons. Thank you for your attention! 14