What Forensic Science Is

It is interdisciplinary. Chemistry, biology, physics, medicine, dentistry, psychology, engineering and now computer science all supply branches. That is the reason a laboratory is organised in divisions, which is the subject of Module II.

It is adversarial in its setting even though it is not adversarial in its method. The scientist works to a scientific standard, then gives evidence in a system where a lawyer is paid to attack it. Much of the practice of the subject exists to survive cross-examination: the notes, the case file, the second examiner's check, the retained sample.

Objectives: what it is for

To establish that an offence has been committed at all. A death may be natural, accidental, suicidal or homicidal, and often only the autopsy and the chemical analysis can say which. A fire may be an accident or arson. A cash shortfall may be theft or bad book-keeping.

To reconstruct what happened. Where did the shot come from, in what order were the injuries caused, was the body moved after death, was the door forced from inside or outside.

To identify. Both the victim and the offender. Identification of the dead from bones, teeth and fingerprints, and identification of the offender from what he left behind or took away.

To link, and equally to exclude. A link is proved between a person, a place and a thing. The mirror of that objective is exclusion, and it is not a lesser result: an accused eliminated by a blood group or a profile has been served by the same science that would have implicated him.

To provide evidence a court can act on. An opinion that cannot be explained, or that rests on material nobody can trace, is not evidence however good the science was.

To prevent and to deter. This objective belongs to Module III, and it is the reason the syllabus separates control and prevention from detection.

Importance: why the criminal justice system needs it

Because eyewitnesses are unreliable and are known to be. Indian criminal trials rest heavily on oral testimony, and oral testimony in India is subject to a further pressure that is not present everywhere: witnesses turn hostile. A scientific exhibit does not resile from its statement under threat.

Because a great many offences have no witness at all. Poisoning, sexual offences, cheating by electronic means, and most homicides committed indoors.

Because it protects the innocent. This is the half of the argument that most answers omit, and it is the half an examiner rewards. The same laboratory that reports a match reports an exclusion.

Because the law now requires it. Section 176(3) of the Bharatiya Nagarik Suraksha Sanhita, 2023 obliges the officer in charge of a police station, on information of an offence punishable with seven years or more, to cause a forensic expert to visit the scene, once the State Government has notified the date. That is a duty, not a good practice, and it is taken up in [The Forensic Expert at the Crime Scene: Section 176(3)].

Because the volume and the kind of crime have changed. Offences committed through a computer, offences committed by an organised group across three States, and offences whose proceeds move through several bank accounts in a day cannot be investigated by knocking on doors.

What forensic science is not

It is not infallible. Whole disciplines once thought reliable have been discredited. The paraffin glove test for gunshot residue reacted to fertiliser and to urine. Comparative bullet lead analysis was abandoned. Bite mark comparison has been withdrawn from serious use in several countries. A student who presents the subject as certainty has not understood it.

It is not investigation. The laboratory answers what it is asked. It does not decide whom to suspect, and it cannot correct an investigating officer who sends the wrong exhibits or asks the wrong question.

It does not decide guilt. The scientist proves that this bullet came from that pistol. Whether the accused fired it is for the court.

It is not the same as medical jurisprudence. Forensic medicine applies medicine to legal questions. Medical jurisprudence runs the other way and deals with the law that governs the doctor. The two are taken apart in [Forensic Medicine and Medical Jurisprudence].

A worked example: the same fact seen four ways

A watchman at a godown in Bhiwandi is found dead with a head injury. An iron rod lies beside him. Suspicion falls on Nitin, a former employee.

The question the investigating officer asks himself is whether Nitin did it. That is not a question science can answer and the laboratory will not be asked it.

The questions the laboratory can be asked are four, and each belongs to a different division. Is the stain on the rod human blood, and of what group and profile, which is biology and serology. Is the shape of the wound consistent with this rod, which is forensic medicine. Are there fingerprints on the rod and whose, which is the fingerprint bureau. Is the soil on Nitin's sandals the same as the soil at the godown gate, which is trace evidence.

Suppose the answers come back: the blood is the watchman's, the wound is consistent with the rod, the print on the rod is not Nitin's and belongs to nobody on record, and the soil comparison is inconclusive. That is a good day's science and it proves that the rod was the weapon. It does not implicate Nitin at all, and the print that is not his is a fact that helps him.

Now suppose the officer had sent only the rod, and had not taken Nitin's sandals or a control sample of the gate soil. The soil question can never be answered afterwards, because the sandals will have been worn and the gate will have been walked over. That is the difference between forensic science and the scientific investigation of crime, and it is why the collection stage is in the definition.

Distinctions that carry marks

Quick revision

• Definition: the application of the principles and techniques of science to the identification, collection, preservation, examination and interpretation of material connected with an alleged offence, to assist the administration of justice.
• Nature: applied, comparative, inferential with a scale of certainty, interdisciplinary, and practised in an adversarial setting.
• Objectives: establish that an offence occurred, reconstruct, identify, link and exclude, produce usable evidence, and prevent.
• Importance: unreliable and hostile witnesses, offences with no witness, protection of the innocent, the statutory duty in section 176(3), and the changed nature of crime.
• Limits: not infallible, not investigation, does not decide guilt.

Test yourself

1. Give a full definition of forensic science and explain why the word "alleged" appears in it. It is the application of the principles and techniques of science to the identification, collection, preservation, examination and interpretation of material found in connection with an alleged offence, to assist the administration of justice. "Alleged" is there because the scientist works before guilt is established and must be as ready to exclude a suspect as to implicate one.

2. Name three features of the nature of forensic science. It is applied rather than pure, since the question comes from the investigator. It is comparative, since almost every examination compares a questioned item with a known one. It is inferential and reports a strength of opinion rather than a bare yes or no.

3. State four objectives of forensic science. To establish that an offence was committed, to reconstruct the event, to identify persons and things, and to link or exclude a suspect. Providing court-usable evidence and preventing crime are the fifth and sixth.

4. Why is the protection of the innocent an argument for forensic science rather than against it? Because exclusion and implication come from the same examination. A profile that does not match, or a blood group that is inconsistent, removes a suspect on objective grounds that no amount of oral evidence can supply.

5. Give two examples of forensic techniques that were once accepted and are now discredited or doubted. The paraffin glove or dermal nitrate test for gunshot residue, which reacted to common substances such as fertiliser, and comparative bullet lead analysis, which was abandoned. Bite mark comparison is a third and is now heavily doubted.