Evidence and the Forensic Sciences

Forensic Science

In its broadest sense, Forensic Science can be considered the application of science to those criminal and civil laws that are enforced by police agencies in a criminal justice system.
Which of the ''sciences'' can be ''forensic''? Just about any science can be a forensic science if it can have any application to justice or judicial matters. It is a very large ''umbrella'' of expert fields.

Edmond Locard (1923): "theory of interchange":
"that the person or persons at the scene when a crime is committed will almost always leave something and take something away"

The doctrine of exchange or transfer is based on (Wagner, 1986):
  1. The perpetrator will take away traces of the victim and the scene
  2. The victim will retain traces of the perpetrator and may transfer traces of himself on the perpetrator.
  3. The perpetrator will leave behind traces of himself at the scene

Different Types of Evidence


Physical VS Non-physical evidence: 

Evidence is that which tends to support a contention, or show that something is the case, or prove the existence of something.

  • Physical evidence is real and consists of things or objects
  • Non-physical evidence relates to things like verbal testimony about what a witness saw and remembered, and to things like a 2 or 3-dimensional scale diagram or model of a crime scene, or a chart or graph of observations or from an analytical instrument

Known VS Unknown evidence:

  • Unknown evidence is material found at a scene but where its source is unknown, whether blood, a bullet, or stain, fibre, etc. 
  • Known evidence is evidence taken from a known source at a scene and which is used in comparison with unknown evidence or evidence found later.

Class VS Individual Evidence:

  • Class evidence relates to the category of material that a piece of evidence came from, and is non-specific
  • Individual evidence relates to the actual object, person, victim or perpetrator that it came from, deals with unique characteristic and is very specific; it is referred to as ''individualisation''.

Analytical Testing in the Laboratory 

Whenever testing is done in a forensic science laboratory (also known as a crime laboratory sometimes), the courts require verification that a test or equipment is working properly, and that the results of a test are credible. This requires positive and negative controls.

  • Positive controls are used to make sure that the chemicals used in a test are pure and functioning correctly, so that there are no false negative results
  • Negative controls are used to make sure that only the target of the test will be tested for, so that there are no false positive results

Physical Evidence

To look at the possible applications of fields of science in forensic work, let us first look at the possible types of physical evidence we could have at a scene of crime.

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.

Physical evidence also does not have to be a tangible substance. It can also be a print or pattern left at the scene. Trace evidence refers to evidence in very small amounts, which may be easily overlooked or lost if not looked for carefully and with the correct techniques employed. Examples of physical evidence include:

Body evidence:

Most evidence from the body includes:
1. A human body or its parts
2. Body trace evidence:
a. fluids such as blood, semen, urine, stool, sweat and saliva
b. body tissues and hair
3. From clothing and other attachments (e.g. tampons) applied to or worn on the body

Non-body evidence:

The following are only some of the more frequently used evidence:
1. Questioned documents
2. Illicit drugs and controlled chemical substances
3. Fire and chemical residues in cases or arson, including petroleum products
4. Explosive residues and casing of detonators, etc., in cases of bombings
5. Fabrics (clothing and coverings) and fibres
6. Prints and Impressions: Fingerprints, sole prints, tyre prints, etc.
7. Firearms and Ammunition
8. Powder residues, glass, paints and plastics
9. Soils, elemental analysis / mineralogy and metallurgy
10. Tool marks and Serial numbers
11. Vehicle Lights
12. Wood, pollen and other vegetative matter, incl. debris and other foreign materials in wounds and clothing
13. Adhesives and dyes
14. Ropes and cords
15. Audio-visual / electronic devices/computers
16. Miscellaneous

The Value of Physical Evidence

Physical evidence may be utilized in forensic investigations in the following meaningful areas:

1. Defining the elements of the crime. Such as the identification and quantitation of a drug or controlled substance or the determination of the quantity of alcohol in the blood of a person suspected of driving while intoxicated.
2. Providing investigative leads for a case. An example of this would be the identification of a vehicle type in a hit-and-run case through automotive paint and glass analysis.
3. Linking a crime scene or a victim to a suspect. This like may be provided through analysis of various types of physical evidence such as hair, blood, semen, and fingerprints.
4. Corroborating or refuting a suspect's statement of alibi. In a fatal gunshot case, the examination of bloodstained patterns at the scene and on a suspects clothing may establish whether a victim was struggling with an assailant as may be claimed or conversely show that the victim was in a totally different position or location when the shot was fired.
5. Identifying a suspect. The identification of a suspect is not limited to but often established through fingerprint comparison or DNA profiling.
6. Inducing a confession of a suspect. In some cases presenting factual information to a suspect established through the examination of physical evidence, such as the victim's blood identified on their clothing of fingerprints identified on a weapon, will encourage the person to admit involvement in a crime.
7. Exonerating the innocent. Physical evidence may be found that may prove a person did not commit a crime. This is often referred to as exculpatory evidence.
8. Providing expert testimony in court. The presentation of physical evidence in court by an expert is the ultimate test of the validity of the evidence.

The Functions of the Forensic Scientist and the Forensic Laboratory

1. Analysis of physical evidence
2. Provision of expert testimony
3. Furnishing training in the proper recognition, collection, and preservation of physical evidence

Glossary of Forensic Science

1. Forensic Criminalistics
This rather too-broad general term is used to refer to all physical and other evidence found at crime scenes and the science of their comparative study and examination, for the purposes of identification and tracing of and matching between perpetrator and scene, or perpetrator and victim, or victim and scene.

Criminalistics is the overall wide field where all natural sciences are applied in investigation, and includes most of the areas of special attention additionally mentioned below. It includes firearms and explosives examination, toolmark examination, document examination, biologic examination, physical analysis, chemical analysis, soil analysis, and identification, etc.. Voiceprint comparison is a recently developed specialty of crime laboratories. Many techniques including X-ray films, photography, fingerprinting, dental comparison, and blood typing may also be included here as a wider definition of the term.

The specific fields below are well-developed areas of Forensic Criminalistics:

2. Forensic Medicine (alt. Forensic Pathology)
Forensic Medicine is that branch of medicine where emphasis is laid on the role of the doctor, his obligations and responsibilities towards his patients and towards the administration of justice in criminal as well as civil cases.

Forensic Medicine can be divided into two distinct but not exclusive specialities: Clinical Forensic Medicine and Forensic Pathology.

Clinical Forensic Medicine
Clinical Forensic Medicine is a discipline of Medicine which deals with the examination and completion of medico-legal reports on living patients in instances where legal proceedings may follow from an incident.

Forensic Pathology
Pathology in general refers to the study of disease and tissue injury by scientific methods, while Forensic Pathology relates to the investigation of unnatural disease and trauma. The investigation usually seeks to determine the cause of unnatural and suspicious deaths by means of a post-mortem/autopsy examination.

3. Forensic Anthropology
Forensic anthropologists are experts in the identification of bones and work almost solely with skeletal remains, identify whether bones are human or animal, age, race, gender, stature, handedness, etc. This is not an easy task and medical doctors often find that they are very unsure about this field. The anthropologists also help with facial reconstruction of an unknown individual.

4. Forensic Odontology
The value of a person's dental (teeth) arrangement is without doubt in forensic identification work. It could be that:

  • Dental records can be used to match with the teeth found in human remains of a mass disaster such as an aircraft crash, a decomposed or skeletonised body, or the remains of a charred body found, all of which are otherwise difficult to identify. Victims of a disaster or homicide may be identified by a comparison of their dental charts and X-rays to the dental evidence from the victims.
  • In abuse cases, particularly child abuse cases, bite marks profiles may be used to compare with suspected perpetrators;
  • ? In other cases, where bite mark impressions may be used to identify the suspect. Bitemarks in apples, cheese, chewing gum, and other media as well as on a victim's body may be studied by these scientists.
5. Forensic Toxicology
Toxicology deals with the detection of toxic substances and drugs in body tissues and fluids. Forensic Toxicology is the study of poisons, the chemical and physical properties of toxic substances and their physiological effects on the living organism.
The toxicologist analyses biological fluids and tissue from victims who are thought to have been poisoned accidentally or purposely. The toxicologist, as distinct from the forensic chemist, primarily handles biological materials and can detect poisons in blood, urine, spinal fluid, gastric contents, bile, and tissues.

6. Forensic Chemistry
The forensic chemist handles the identification of a variety of other chemicals that may be found or associated with a scene of crime, such as the identification of accelerants in cases of arson, the identification of industrial, agricultural or military chemicals, or the identification of explosive chemicals, etc. It may also involve the identification of fibres, paints, clays, soils, glass, etc.

7. Forensic Entomology
The utilisation of entomological data (study of local insect life) to establish the circumstances and time of death by means of identifying insect species and the stage of their life cycle at which they are found on the bodies they infest. A limited usefulness in detecting poisons by insect examination is possible.

8. Forensic Engineering
The investigation of accidents involving vehicles in traffic, recreational vehicles, or aircraft, or industrial, fire, electrical, or metal fatigue accidents has brought into the picture those who develop and apply engineering principles to the solution of the cause of accidents. Thus, forensic engineering has been added to the other areas of the forensic sciences. These scientists look at failure analysis of structural elements of buildings, bridges, etc., and other structures.

Automobile crashes (accident reconstruction) are one area of a great deal of work. Balconies of buildings that collapse, or spectator stands at a sports event, etc., are those that stand out in the literature. Aircraft crashes and the examination and analysis of the ''black box'' from a crash are an example as well.

9. Forensic Document Examination (Questioned Documents [QD])
The Forensic Document Examiner's work includes the examination of handwriting, ink, paper, typewriter or printer impressions, or any other form of writing or printing that may have been used in a case. The expertise includes detection of counterfeiting and carious types of fraud involving government paper, checks, forms, money, and credit cards of the possible falsification of entries, e.g. in a ship's log.

10. Forensic Ballistics
The forensic ballistic examiner examines firearms and projectiles (bullets and cartridge cases) found at crime scenes in a ballistic laboratory, where he identifies and matches a fired bullet to a cartridge case or forearm, by means of microscopic comparison of rifling marks, etc. He may also test-fire firearms in controlled conditions for the matching of rifling marks and also for the determination of the range of fire of a particular gun.

11. Forensic Toolmark Examination
Similar to the markings left by a gun on bullets and cartridges, marks left on surfaces and objects by tools and instruments are studied by the Forensic Toolmark Examiner. The Forensic Ballistic Examiner often fulfills this role as well - they may be one and the same as the examination system in the laboratory may be very similar. The analysis of toolmarks takes advantage of the observation that toolmarks may be individualisable.

12. Forensic Prints Analysis:
The analyses of the following are also done in this context:

  • Fingerprints (dactyloscopy)
  • serial numbers, their erasing and their restoration
  • sole-prints
  • tyre-prints

13. Forensic Botany
The examination of plant life, insects, soil, trees, dirt, seeds, and pollen are occasionally used and can be a means of developing new resources to a forensic investigation.

14. Forensic Serology and DNA typing (molecular biology)
Application of techniques in immunology, blood group serology and molecular biology (DNA technology) for:

Human identification
Paternity testing
Linkage of the victim and /or assailant to a particular incident
DNA technology involves the determination of the DNA profile of the nuclear chromosomal material that is unique to each and every person (DNA "fingerprinting"). This technique has transformed identification methods in forensic science in recent years.

15. Forensic Trichology:
Can use this term for hair analysis.

16. Forensic Radiology
The utilisation of radiography in visualising injuries, foreign bodies such as bullets, etc. and anatomical traits, including ageing for medico-legal and evidential purposes. It also plays an important role in identification of unknown remains.

17. Forensic Photography
Application of photography in establishing a permanent record of forensic clinical and pathological evidence that is transient due to healing or post-mortem deterioration / decomposition. It is a useful adjunct to the post-mortem or other medico-legal report.

18. Forensic Psychiatry
The forensic psychiatrist plays an important role in forensic cases, e.g. assessing a person's fitness to stand trial, criminal profiling and conducting 'psychological autopsies' in suicide cases.

19. Forensic Psychology:
This deals with criminal study of offenders and crime psychology (Criminology) and when it is applied to forensic investigation it usually involves e.g. the criminal profiling of serial killers, etc.

20. Forensic Biology:
This too non-specific a category, as it includes all the biological examinations of pathology, anthropology, odontology, botany, serology and DNA typing, and even hair analysis.

21. Miscellaneous areas of Forensic involvement:

  • Forensic Nursing
  • Forensic Artistry: where facial identikits are made for publication for identification purposes and use in investigation
  • Forensic Facial Reconstruction: here, the anthropologist, odontologist and the artist often combine their talents and abilities for this work and, for computerised application of this work, the use of computer technology.
  • Lie Detection Analysis (Polygraph testing)

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