Forensic Science Basics
Unit – 2 INTRODUCTION TO
FORENSIC SCIENCE
Laws and Principles of Forensic Science
• Forensic science is concerned with the reconstruction of unique events — attempting to determine
– what happened – how it happened
– where and when it happened – who was involved
• Each crime occurs under a different combination of circumstances affected by an enormous number of variables, and is thus nonreplicable
• Forensic scientists deals with samples that are limited in size and quality, and which have an unknown history
• Legal process imposes unique constraints and characteristics on forensic science
Law of individuality Principle of exchange
Law of progressive change Principle of comparison Principle of analysis
Law of probability
The laws and principles of all the natural sciences are the bases of forensic science. In addition, it has
developed its own principles which are as follows:
• Every object, natural or man-made, has an individuality which is not duplicated in any other object. This principle, at first sight appears to be contrary to common beliefs and observations.
• The grains of sand or common salt , seeds of plants or twins look exactly alike. Likewise, man-made objects: coins of the same denomination made in the same mint, currency notes printed with the same printing blocks one after the other (excluding serial number) and typewriters of the same make, model and batch appear to be indistinguishable. Yet the individuality is always there. It is due to small flaws in the materials, in the arrangement of the crystals, imperfect stamping or due to inclusions of some extraneous matter. The individuality has been verified in certain fields.
• The law of individuality is of fundamental importance in forensic science. Anything and everything involved in a crime, has an individuality. If the sane is established , it connects the crime and the criminal.
Law of individuality
• Contact exchanges traces is the principle of exchange. It was first enunciated by the French scientist, Edmond Locard.
• According to the principal, when a criminal or his instruments of crime come in contact with the victim or the objects surrounding him, they leave traces. Likewise, the criminal or his instruments pick up traces from the same contact. Thus, a mutual exchange of traces like takes place between the criminal, the victim and the objects involved in the crime If these traces are identified to the original source, viz., the criminal or his instrument (or vice versa), they establish the contact and pin the crime on to the criminal. The principal of exchange is aptly demonstrated in hit and run cases and in offences against person.
If the investigating officer is able to establish the points of contact , he is likely to gather physical clues:
• If a criminal enters the premises through a ventilator , he leaves his foot prints in dust on the sill.
• If he breaks a window or a door, the jimmy leaves its marks on the wooden frame.
Principle of exchange
Principle of recovery
• Do not harm (evidence)
• Nothing should be added, damaged or obliterated in the recovery process
• Particular attention should be paid to avoiding contamination, a concern that gains increasing importance with each advance in analytical sensitivity.
• Where there is risk of losing or damaging evidence, appropriate experts should be called in.
• Exhibit items should be safely and securely packaged as soon as possible.
• If an object is portable, transfer to the lab for evidence recovery under controlled conditions.
• Do no harm to yourself! Crime scenes and recovered evidence may pose biological or chemical hazards.
• Health & safety measures for collecting and transporting evidence.
Everything changes with the passage of time. The rate of change varies tremendously with different objects.
1. The criminal undergoes rapid changes. If he is not apprehended in time, he becomes unrecognizable except perhaps through his fingerprints, bone fractures or other characteristics of permanent nature which are not always available.
2. The scene of occurrence undergoes rapid changes. The weather, the vegetable growth, and the living beings (especially human-beings) make extensive changes in comparatively short periods. Longer the delay in examining the scene, greater will be the changes. After some time ,the scene may become unrecognizable.
3. The objects involved in crime change gradually, the firearm barrels loosen , metal objects rust, the shoes suffer additional wear and tear and the tools acquire new surface patterns. In course of time the objects may loose all practical identity vis-à-vis a particular crime.
The principle, therefore, demands prompt action in all aspects of criminal investigation.
Law of progressive change
• Improper sampling and contamination render the best analysis useless. The principle emphasizes the necessity of correct sampling and correct packing for effective use of experts.
For example:-
A small amount of dust is recovered from a small sticky patch of the shoe of a culprit. The investigating officer collects about two kilograms of soil from the scene packs it in tin and sends it as a control sample. The results of comparison are inconclusive.
Why?
Principle of analysis
Only the like can be compared is the principle of comparison.
It emphasizes the necessity of providing like samples and specimens for comparison with the questioned items:
1. In a murder case, a bullet is recovered from the deceased. The expert opines that the bullet has been fired from a firearm firing high velocity projectiles like a service rifle. It is futile to send shotguns, pistols or revolvers as the possible suspect firearm.
2. A bunch of hair is recovered from the hands of a deceased. The expert opines that the hair belong to a Negroid person. Hair from persons of white races for comparison will not be of any use.
3. The questioned writing is found to have been writing with a ball pen.
To send fountain pen as a likely instrument of writing is futile.
Principle of comparison
• All identifications, definite or indefinite, are made, consciously or unconsciously, on the basis of probability.
• Probability is the mathematical concept.
• It determines the chances of occurrence of a particular event in a particular way out of a number of ways in which the event can take place or fail to take place with equal facility.
If P= represents probability
Ns = the number of ways in which the event can successfully occur (with equal facility) and
Nf = the number of ways in which it can fail(with equal facility), Then the probability of success is given by the formula:
P= Ns/ Ns+ N2.
Law of Probability
Principle of Presentation
• Working within an ethical framework, a forensic scientist should fully disclose and present impartial evidence which is readily understandable and neither overstated nor understated.
• Full disclosure of all facts, assumptions, data, conclusions and interpretations should be made.
– Lab report: Complete & retained.
• He or she should not be an advocate for either side of the case at hand; it is, however, to be expected that a forensic scientist will be an advocate for his or her opinion.
• However, the forensic scientist should be prepared to change an opinion whenever background circumstances or assumptions change, or new information becomes available.
Branches of Forensic Science
Toxicology
• Toxicology deals with the detection of toxic substances and drugs in body tissues and fluids.
• The toxicologist analyzes biological fluids and tissues 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.
Anthropology
• Forensic anthropologists are experts in the identification of bones and skeletal remains. Their studies provide information about sex, race, age, and time of death.
• They may also lend support to investigations concerning living cases such as a mix-up of children in a hospital nursery or skeletal identification of persons involved in immigration problems.
• The forensic anthropologist may be extremely helpful in mass disasters with considerable skeletal remains or in cases of mass burials.
• A recent application of this expertise was reconstructing the face of a skeletonized head.
Odontology
• The odontologist, or dentist, provides information through examination of teeth and dental prostheses. 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.
• Bitemarks in apples, cheese, chewing gum, and other media, as well as on a victim’s body, may be studied by these scientists.
• This form of expertise may also be used in living cases, as the examination of teeth is helpful where there is a possibility of a hospital mix-up of children, as such examinations may depend upon the presence on inherited characteristics in teeth.
Biology
• The examination of plant life, insects, soil, trees, dirt, seeds, and pollen, as well as blood analysis, can be a means of developing new resources to a forensic investigation
Questioned Documents
• Questioned document (QD) examinations were reported as far back as Roman times, when cases of forged documents were described.
• The modern use of typewriters and computer printers has added significantly to the activities of questioned document examiners.
• The QD 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.
• This expertise includes detection of counterfeiting and various types of fraud involving government paper, checks, forms, money, and credit cards or the possible falsification of entries in a ship’s log.
• The investigation of computer fraud may also examine the validity of printout material
Forensic psychology
• It is the intersection between psychology and the justice system.
It involves understanding criminal law in the relevant jurisdictions in order to be able to interact appropriately with judges, attorneys and other legal professionals.
• It is concerned with collecting, examining, and presenting evidence to help facilitate a legal decision. Within the legal system, forensic psychology provides a means for being able to enforce the law while taking human behavior into consideration.
• A forensic psychologist may be called upon to differentiate between criminal behavior and human behavior that may be caused by a psychological imbalance.
Physics
• Types of evidences examined
The application of physics for purposes of civil or criminal law.
• Indirectly, physics has contributed to forensic science via the invention of the microscope, the electron microscope, the mass spectrometer, and optical spectrometers; but directly, its role in forensic science has been minimal.
• Forensic physics has traditionally involved the measurement of density (soil and glass examination), index of refraction, and birefringence (fiber analysis, glass examination).
Ballistics
• Ballistics is the science of mechanics that deals with the flight, behavior, and effects of projectiles, especially bullets, gravity bombs, rockets, or the like; the science or art of designing and accelerating projectiles so as to achieve a desired performance.
Forensic Entomology
• Forensic entomology is the study of the insects associated with a human corpse in an effort to determine elapsed time since death.
• Insect evidence may also show that the body has been moved to a second site after death, or that the body has been disturbed at some time, either by animals, or by the killer returning to the scene of the crime. However, the primary purpose of forensic entomology today is to determine elapsed time since death.
Judicial officer
• A judicial officer is a person with the responsibilities and powers to facilitate, arbitrate, preside over, and make decisions and directions in regard to the application of the law.
• Judicial officers are typically categorized as judges, magistrates, puisne judicial officers such as justices of the peace or officers of courts of limited jurisdiction;
and notaries public and commissioners of oaths.
• The powers of judicial officers vary and are usually limited to a certain jurisdiction.
Role of Police
• Securing the scene
• Questioning
• Assisting in evidence collection
• Documenting
• Arresting/taking into custody
Role of a medico legal expert
• Necessary to determine the cause of death.
Forensic Science Lab
– Processing of the scene of crime, collection, handling, preservation, packaging of the physical evidence
– Sample collection – Quick spot-test kits
– Scanning devices: UV, IR scanning devices
– Items: Gloves, Bags, cotton, cardboard boxes, labeling tools – Photography
1. Observe a problem or questioned evidence.
2. Consider a hypothesis to know the way of crime.
3. Examine, test and analyze those evidence.
4. Determine the significance of the evidence.
5. Formulate a theory based on evaluation of the significance of the evidence
