1-1 PRENTICE HALL ©2008 Pearson Education, Inc. Upper Saddle River, NJ 07458 FORENSIC SCIENCE An...

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PRENTICE HALL ©2008 Pearson Education, Inc. Upper Saddle River, NJ 07458

FORENSIC SCIENCE An IntroductionBy Richard Saferstein

INTRODUCTION

Chapter 1

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Definition• In its broadest definition, forensic science is the

application of science to criminal and civil laws. • The subject matter of this book emphasizes the

application of science to those criminal and civil laws that are enforced by police agencies in a criminal justice system.

• Forensic science owes its origins to individuals such as Bertillon, Galton, Lattes, Goddard, Osborn, and Locard, who developed the principles and techniques needed to identify or compare physical evidence.

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History• Mathieu Orfila—the father of forensic toxicology. • Alphonse Bertillion—devised the first scientific

system of personal identification in 1879.• Francis Galton—conducted the first definitive

study of fingerprints and their classification.• Leone Lattes—developed a procedure to

determine blood type from dried bloodstains.• Calvin Goddard—used a comparison microscope

to determine if a particular gun fired a bullet.• Albert Osborn—developed the fundamental

principles of document examination.

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History• Walter McCrone—utilized microscopy and other

analytical methodologies to examine evidence. • Hans Gross—wrote the first treatise describing

the application of scientific principles to the field of criminal investigation.

• Edmond Locard—incorporared Gross’ principles within a workable crime laboratory.

• Locard’s Exchange Principle—states that when a criminal comes in contact with an object or person, a cross-transfer of evidence occurs.

• Sir Alec Jeffreys—developed the first DNA profiling test in 1984.

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The Crime Lab• The development of crime laboratories in

the United States has been characterized by rapid growth accompanied by a lack of national and regional planning and coordination.

• At present, approximately 350 public crime laboratories operate at various levels of government—federal, state, county, and municipal.

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The Crime Lab• The ever increasing number of crime

laboratories is partly the result of the following:– Supreme Court decisions in the 1960s

responsible for police placing greater emphasis on scientifically evaluated evidence.

– Crime laboratories inundated with drug specimens due to accelerated drug abuse.

– The advent of DNA profiling.

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Technical Support• The technical support provided by crime

laboratories can be assigned to five basic services. – Physical Science Unit incorporates the

principles of chemistry, physics, and geology to identify and compare physical evidence.

– Biology Unit applies the knowledge of biological sciences in order to investigate blood samples, body fluids, hair, and fiber samples.

– Firearms Unit investigates discharged bullets, cartridge cases, shotgun shells, and ammunition.

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Technical Support– Document Unit provides the skills needed for

handwriting analysis and other questioned-document issues.

– Photographic Unit applies specialized photographic techniques for recording and examining physical evidence.

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Technical Support• Optional Services by Full-Service Labs

– Toxicology Unit examines body fluids and organs for the presence of drugs and poisons.

– Latent Fingerprint Unit processes and examines evidence for latent fingerprints.

– Polygraph Unit conducts polygraph or lie detector tests.

– Voiceprint Analysis Unit attempts to tie a recorded voice to a particular suspect.

– Evidence-Collection Unit dispatches specially trained personnel to the crime scene to collect and preserve physical evidence.

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The Scientific Method• Formulate a question worthy of

investigation.

• Formulate a reasonable hypothesis to answer the question.

• Test the hypothesis through experimentation.

• Upon validation of the hypothesis, it become suitable as scientific evidence.

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Skills of a Forensic Scientist• A forensic scientist must be skilled in applying

the principles and techniques of the physical and natural sciences to the analysis of the many types of evidence that may be recovered during a criminal investigation.

• A forensic scientist may also provide expert court testimony.

• An expert witness is an individual whom the court determines possesses knowledge relevant to the trial that is not expected of the average person.

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Skills of a Forensic Scientist• The expert witness is called on to

evaluate evidence based on specialized training and experience that the court lacks the expertise to do.

• The expert will then express an opinion as to the significance of the findings.

• Forensic scientists also participate in training law enforcement personnel in the proper recognition, collection, and preservation of physical evidence.

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The Frye Standard• The Frye v. United States decision set guidelines

for determining the admissibility of scientific evidence into the courtroom.

• To meet the Frye standard, the evidence in question must be “generally accepted” by the scientific community.

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Frye Not Absolute• However, in the 1993 case of Daubert v.

Merrell Dow Pharmaceutical, Inc., the U.S. Supreme Court asserted that the Frye standard is not an absolute prerequisite to the admissibility of scientific evidence.

• Trial judges were said to be ultimately responsible as “gatekeepers” for the admissibility and validity of scientific evidence presented in their courts, as well as all expert testimony.

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Daubert Criteria For Admissibility

• Whether the scientific technique or theory can be tested.

• Whether the technique has been subject to peer review and publication.

• The techniques potential rate of error.

• Existence and maintenance of standards .

• Whether the scientific theory or method has attracted widespread acceptance within a relevant scientific community.

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Special Forensic Science Services• A number of special forensic science

services are available to the law enforcement community to augment the services of the crime laboratory.

• These services include forensic pathology, forensic anthropology, forensic entomology, forensic psychiatry, forensic odontology, computer science, and forensic engineering.

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Special Forensic Science Services• Forensic Psychiatry is an area in which the relationship

between human behavior and legal proceedings is examined.

• Forensic Odontology involves using teeth to provide information about the identification of victims when a body is left in an unrecognizable state. Also investigates bite marks.

• Forensic Engineering is concerned with failure analysis, accident reconstruction, and causes and origins of fires or explosions.

• Forensic Computer Science involves the examination of digital evidence.

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THE CRIME SCENE

Chapter 2

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Physical Evidence• As automobiles run on gasoline, crime

laboratories “run” on physical evidence. • Physical evidence encompasses any and all

objects that can establish that a crime has been committed or can provide a link between a crime and its victim or a crime and its perpetrator.

• But if physical evidence is to be used effectively for aiding the investigator, its presence first must be recognized at the crime scene.

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The Beginning• Forensic science begins at the crime scene.• If the investigator cannot recognize physical

evidence or cannot properly preserve it for laboratory examination, no amount of sophisticated laboratory instrumentation or technical expertise can salvage the situation.

• Here, investigators must recognize and properly preserve evidence for laboratory examination.

• It must be emphasized that the techniques of crime-scene investigation are not difficult to master and certainly lie within the bounds of comprehension of the average police officer.

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The First Steps• The first officer to arrive at the scene is

responsible for securing the crime scene. • First priority should be given to obtaining

medical assistance for individuals in need of it and to arresting the perpetrator.

• As soon as it is possible, extensive efforts must be made to exclude all unauthorized personnel from the scene.

• Once the scene is secured, the preliminary exam must begin.

• Recording of the crime scene becomes a critical piece to the investigation process.

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Recording Methods• Photography, sketches, and notes are the

three methods for crime-scene recording.• Ideally all three should be employed;

however, as is often the case, personnel and monetary limitations may prohibit the utilization of photography at every crime site.

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Photography• The most important prerequisite for

photographing a crime scene is for it to be in an unaltered condition.

• Unless there are injured parties involved, objects must not be moved until they have been photographed from all necessary angles.

• As items of physical evidence are discovered, they are photographed to show their position and location relative to the entire scene.

• After these overviews are taken, close-ups should be taken to record the details of the object itself. – When the size of an item is of significance, a ruler or

other measuring scale may be inserted near the object and included in the photograph as a point of reference.

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Sketches• Once photographs are taken, the crime-scene

investigator will sketch the scene. • Rough Sketch—A draft representation of all

essential information and measurements at a crime scene. This sketch is drawn at the crime scene. It shows all recovered items of physical evidence, as well as other important features of the crime scene.

• Finished Sketch—A precise rendering of the crime scene, usually drawn to scale. This type is not normally completed at the crime scene.

• Unlike the rough sketch, the finished sketch is drawn with care and concern for aesthetic appearance.

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Notes• Note taking must be a constant activity

throughout the processing of the crime scene. • These notes must include a detailed written

description of the scene with the location of items of physical evidence recovered.

• They must identify:– the time an item of physical evidence was discovered.– by whom.– how and by whom it was packaged and marked.– the disposition of the item after it was collected.

• The note taker has to keep in mind that this written record may be the only source of information for refreshing one’s memory.

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Recording the Crime Scene• Investigators have only a limited amount of

time to work a crime site in its untouched state. • The opportunity to permanently record the

scene in its original state must not be lost. • Such records will not only prove useful during

the subsequent investigation but are also required for presentation at a trial in order to document the condition of the crime site and to delineate the location of physical evidence.

• Every step of the investigation should be documented thoroughly with an appropriate method.

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The Preliminary Exam• A lead investigator will start the process of evaluating

the area. – First, the boundaries of the scene must be

determined– Followed by the establishment of the perpetrator’s

path of entry and exit.– The investigator then proceeds with an initial

walk-through of the scene to gain an overview of the situation and develop a strategy for the systematic examination and documentation of the entire crime scene.

• This is done before processing the crime scene for physical evidence.

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The Search• The search for physical evidence at a crime

scene must be thorough and systematic. • The search pattern selected will normally

depend on the size and locale of the scene and the number of collectors participating in the search.

• For a factual, unbiased reconstruction of the crime, the investigator, relying upon his or her training and experience, must not overlook any pertinent evidence.

• Physical evidence can be anything from massive objects to microscopic traces.

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The Search• Often, many items of evidence are clearly

visible but others may be detected only through examination at the crime laboratory.

• For this reason, it is important to collect possible carriers of trace evidence, such as clothing, vacuum sweepings, and fingernail scrapings, in addition to more discernible items.

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Beyond the Crime Scene• The search for physical evidence must extend

beyond the crime scene to the autopsy room of a deceased victim.

• Here, the medical examiner or coroner will carefully examine the victim to establish a cause and manner of death.

• As a matter of routine, tissues and organs will be retained for pathological and toxicological examination.

• At the same time, arrangements must be made between the examiner and investigator to secure a variety of items that may be obtainable from the body for laboratory examination.

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Beyond The Crime Scene• The following are to be collected and sent to the

forensic laboratory:1. Victim’s clothing

2. Fingernail scrapings3. Head and pubic hairs4. Blood (for DNA typing purposes)5. Vaginal, anal, and oral swabs (in

sex- related crimes)6. Recovered bullets from the body7. Hand swabs from shooting victims

(for gunshot residue analysis)

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Packaging• Each different item or similar items collected at

different locations must be placed in separate containers. Packaging evidence separately prevents damage through contact and prevents cross-contamination.

• The well-prepared evidence collector will arrive at a crime scene with a large assortment of packaging materials and tools ready to encounter any type of situation.

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Packaging• Forceps and similar tools may have to be used to

pick up small items. • Unbreakable plastic pill bottles with pressure lids

are excellent containers for hairs, glass, fibers, and various other kinds of small or trace evidence.

• Alternatively, manila envelopes, screw-cap glass vials, or cardboard pillboxes are adequate containers for most trace evidence encountered at crime sites.

• Ordinary mailing envelopes should not be used as evidence containers because powders and fine particles will leak out of their corners.

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Packaging• Small amounts of trace evidence can also be

conveniently packaged in a carefully folded paper, using what is known as a “druggist fold.”

• Although pill bottles, vials, pillboxes, or manila envelopes are good universal containers for most trace evidence, two frequent finds at crime scenes warrant special attention.

• If bloodstained materials are stored in airtight containers, the accumulation of moisture may encourage the growth of mold, which can destroy the evidential value of blood.

• In these instances, wrapping paper, manila envelopes, or paper bags are recommended packaging materials.

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Chain of Custody• Chain of Custody—A list of all persons who came

into possession of an item of evidence.• Continuity of possession, or the chain of custody,

must be established whenever evidence is presented in court as an exhibit.

• Adherence to standard procedures in recording the location of evidence, marking it for identification, and properly completing evidence submission forms for laboratory analysis is critical to chain of custody.

• This means that every person who handled or examined the evidence and where it is at all times must be accounted for.

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Obtaining Reference Samples• Standard/Reference Sample—Physical evidence

whose origin is known, such as blood or hair from a suspect, that can be compared to crime-scene evidence.

• The examination of evidence, whether it is soil, blood, glass, hair, fibers, and so on, often requires comparison with a known standard/reference sample.

• Although most investigators have little difficulty recognizing and collecting relevant crime-scene evidence, few seem aware of the necessity and importance of providing the crime lab with a thorough sampling of standard/reference materials.

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Special Forensic Science Services• Forensic Pathology involves the

investigation of unnatural, unexplained, or violent deaths.– Forensic pathologists in their role as medical

examiners or coroners are charged with determining cause of death.

– The forensic pathologist may conduct an autopsy which is the medical dissection and examination of a body in order to determine the cause of death.

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Special Forensic Science Services• After a human body expires there are several

stages of death.– Rigor mortis results in the shortening of muscle

tissue and the stiffening of body parts in the position at death (occurs within the first 24 hrs. and disappears within 36 hrs.).

– Livor mortis results in the settling of blood in areas of the body closest to the ground (begins immediately on death and continues up to 12 hrs.).

– Algor mortis results in the loss of heat by a body (a general rule, beginning about an hour after death, the body loses heat by 1 to 1 1/2 degrees Fahrenheit per hour until the body reaches the environmental temperature).

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Special Forensic Science Services• Forensic Anthropology is concerned

primarily with the identification and examination of human skeletal remains.

• Forensic Entomology is the study of insects and their relation to a criminal investigation, commonly used to estimate the time of death.

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PHYSICAL EVIDENCE

Chapter 3

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Physical Evidence• It would be impossible to list all the objects that

could conceivably be of importance to a crime.• Almost anything can be Physical Evidence.• Although you cannot rely on a list of categories,

it is useful to discuss some of the most common types of physical evidence.

• The purpose of recognizing physical evidence is so that it can be collected and analyzed.

• It is difficult to ascertain the weight a given piece of evidence will have in a case as ultimately the weight will be decided by a jury.

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Types of Physical Evidence• Blood, semen, and saliva• Documents• Drugs• Explosives• Fibers• Fingerprints• Firearms and

ammunition• Glass• Hair• Impressions• Organs and physiological

fluids

• Paint

• Petroleum products

• Plastic bags

• Plastic, rubber, and other polymers

• Powder residues

• Soil and minerals

• Tool marks

• Vehicle lights

• Wood and other vegetative matter

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Purpose of Examining Physical Evidence

• The examination of physical evidence by a forensic scientist is usually undertaken for identification or comparison purposes.

• Identification has, as its purpose, the determination of the physical or chemical identity of a substance with as near absolute certainty as existing analytical techniques will permit.

• A comparison analysis subjects a suspect specimen and a standard/reference specimen to the same tests and examinations for the ultimate purpose of determining whether or not they have a common origin.

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Identification• The object of an identification is to determine the

physical or chemical identity with as near absolute certainty as existing analytical techniques will permit.

– The process of identification first requires the adoption of testing procedures that give characteristic results for specific standard materials.

– Once these test results have been established, they may be permanently recorded and used repeatedly to prove the identity of suspect materials.

– Second, identification requires that the number and type of tests needed to identify a substance be sufficient to exclude all other substances.

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Common Types of Identification• The crime laboratory is frequently requested to

identify the chemical composition of an illicit drug.

• It may be asked to identify gasoline in residues recovered from the debris of a fire, or it may have to identify the nature of explosive residues—for example, dynamite or TNT.

• The identification of blood, semen, hair, or wood are also very common and, as a matter of routine, include a determination for species origin.

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Comparison• A comparative analysis has the important role

of determining whether or not a suspect specimen and a standard/reference specimen have a common origin.

• Both the standard/reference and the suspect specimen are subject to the same tests.

• The forensic comparison is actually a two-step procedure. – First, combinations of select properties are chosen

from the suspect and the standard/reference specimen for comparison.

– Second, once the examination has been completed, the forensic scientist must be prepared to render a conclusion with respect to the origins.

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Role of Probability• To comprehend the evidential value of a

comparison, one must appreciate the role that probability has in ascertaining the origins of two or more specimens.

• Simply defined, probability is the frequency of occurrence of an event.

• In flipping a coin, probability is easy to establish.

• With many analytical processes exact probability is impossible to define.

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Classifying Characteristics• Individual Characteristics

– Evidence that can be associated to a common source with an extremely high degree of probability is said to possess individual characteristics.

• Class Characteristics

– Evidence associated only with a group is said to have class characteristics.

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Individual Characteristics• In all cases, it is not possible to state with

mathematical exactness the probability that the specimens are of common origin.

• It can only be concluded that this probability is so high as to defy mathematical calculations or human comprehension.

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Individual Characteristics• Examples:

– the matching ridge characteristics of two fingerprints

– the comparison of random striation markings on bullets or tool marks

– the comparison of irregular and random wear patterns in tire or footwear impressions

– the comparison of handwriting characteristics– the fitting together of the irregular edges of broken

objects in the manner of a jigsaw puzzle – matching sequentially made plastic bags by striation

marks running across the bags

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Class Characteristics• Surprising to the inexperienced forensic

scientist is the frequent inability of the laboratory to relate physical evidence to a common origin with a high degree of certainty.

• Evidence is said to possess class characteristics when it can be associated only with a group and never with a single source.

• Here again, probability is a determining factor.• Nevertheless, the high diversity of class

evidence in our environment makes their comparison very significant in the context of a criminal investigation.

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Class Evidence

• One of the current weaknesses of forensic science is the inability of the examiner to assign exact or even approximate probability values to the comparison of most class physical evidence.

• For example, what is the probability that a nylon fiber originated from a particular sweater, or that a paint chip came from a suspect car in a hit and run?

• There are very few statistical data available from which to derive this information, and in a mass-produced world, gathering this kind of data is increasingly elusive.

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Class Evidence

• One of the primary endeavors of forensic scientists must be to create and update statistical databases for evaluating the significance of class physical evidence.

• Most items of physical evidence retrieved at crime scenes cannot be linked definitively to a single person or object.

• The value of class physical evidence lies in its ability to provide corroboration of events with data that are, as nearly as possible, free of human error and bias.

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Class Evidence

• The chances are low of encountering two indistinguishable items of physical evidence at a crime scene that actually originated from different sources.

• When one is dealing with more than one type of class evidence, their collective presence may lead to an extremely high certainty that they originated from the same source.

• Finally, the contribution of physical evidence is ultimately determined in the courtroom.

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Crossing Over• Crossing over the line from class to individual

does not end the discussions.• How many striations are necessary to

individualize a mark to a single tool and no other? – How many color layers individualize a paint chip to a

single car? – How many ridge characteristics individualize a

fingerprint?– How many handwriting characteristics tie a person to

a signature?

• These are all questions that defy simple answers and are the basis of arguments.

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Natural vs. Evidential Limits• There are practical limits to the properties and

characteristics the forensic scientist can select for comparison. – Modern analytical techniques have become so

sophisticated and sensitive that natural variations in objects become almost infinite.

– Carrying natural variations to the extreme, no two things in this world are alike in every detail.

– Evidential variations are not the same as natural variations.

– Distinguishing variations of evidential use from natural variations is not always an easy task.

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Using Physical Evidence• As the number of different objects linking an

individual to a crime scene increases, so does the likelihood of that individual’s involvement with the crime.

• Just as important, a person may be exonerated or excluded from suspicion if physical evidence collected at a crime scene is found to be different from standard/reference samples collected from that subject.

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Forensic Databases• The Integrated Automated Fingerprint Identification System

(IAFIS), a national fingerprint and criminal history system maintained by the FBI.

• TheCombined DNA Index System (CODIS) enables federal, state, and local crime laboratories to electronically exchange and compare DNA profiles.

• The National Integrated Ballistics Information Network (NIBIN) allows firearm analysts to acquire, digitize, and compare markings made by a firearm on bullets and cartridge casings.

• The International Forensic Automotive Paint Data Query (PDQ) database contains chemical and color information pertaining to original automotive paints.

• SICAR (shoeprint image capture and retrieval) is a shoeprint database.

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Reconstruction• The method used to support a likely sequence

of events by the observation and evaluation of physical evidence, as well as statements made by those involved with the incident, is referred to as reconstruction.

• Crime-scene reconstruction relies on the combined efforts of medical examiners, criminalists, and law enforcement personnel to recover physical evidence and to sort out the events surrounding the occurrence of a crime.

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The Role of Physical Evidence• The physical evidence left behind at a crime

scene plays a crucial role in reconstructing the events that took place surrounding the crime.

• Although the evidence alone does not describe everything that happened, it can support or contradict accounts given by witnesses and/or suspects.

• Information obtained from physical evidence can also generate leads and confirm the reconstruction of a crime to a jury.

• The collection and documentation of physical evidence is the foundation of a reconstruction.

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Summing It Up• Reconstruction is a team effort that involves

putting together many different pieces of a puzzle.

• The right connections have to be made among all the parts involved so as to portray the relationship among the victim, the suspect, and the crime scene.

• If successful, reconstruction can play a vital role in aiding a jury to arrive at an appropriate verdict.

• The recognition, collection, and analysis of physical evidence is the foundation to successful reconstruction, but only part of the process.

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