Unit 3: Functioning of Forensic Sciences Laboratory

FSC100 — Introduction To Forensic Science 7 min read

Forensic science laboratories (FSLs) convert crime-scene material into court-admissible evidence through a chain of specialised divisions bound by common scientific principles. In India the system is tiered: the Directorate of Forensic Science Services (DFSS) under the Ministry of Home Affairs oversees Central Forensic Science Laboratories (CFSLs), while each state runs a State FSL (SFSL) with Regional (RFSL) and Mobile units below it. This unit establishes how such a laboratory is organised, what each branch does, and the quality and legal framework that makes its findings defensible.

Purpose: the FSL applies natural-science methods to physical evidence so that facts about a crime can be established objectively for investigators and courts.
Locard's principle as foundation: "every contact leaves a trace" is the assumption that any transfer of evidence is analysable — it underpins every division discussed below.
Independence: laboratories are kept administratively separate from investigating police to protect impartiality of results.
Traceability: every exhibit carries a documented chain of custody from seizure to reporting, without which analysis is worthless.
Tiered coverage: CFSL (national/complex cases), SFSL (state cases), RFSL/Mobile (local and scene-based work).

II. Organisational Structure of Forensic Science Laboratories

How authority, exhibits and reports flow through the laboratory.

A. Hierarchy and reporting lines

A forensic laboratory is a pyramid with a single scientific head and specialised divisions beneath.

Director / Chief Forensic Scientist: administrative and scientific head; signs off contested reports and represents the lab in court.
Deputy / Joint Directors: supervise groups of divisions and manage caseload allocation.
Assistant Directors / Senior Scientific Officers: head individual divisions (e.g. Biology, Chemistry).
Scientific Officers and Assistants: perform bench analysis and instrumentation.
Support cadre: exhibit clerk (malkhana), photographers, IT and administrative staff.

B. Central vs. State laboratories

The two tiers differ in jurisdiction and case complexity.

CFSL (Central): located at Chandigarh, Hyderabad, Kolkata, Guwahati, Bhopal, Pune; handle inter-state cases, high-profile matters and referrals; CFSL Delhi works under the CBI.
SFSL (State): one per state under the Home Department; handle the bulk of routine state casework, supported by RFSLs and Mobile units for faster scene response.

C. Exhibit-flow and chain of custody

Structure exists to preserve evidence integrity as items move between divisions.

Receipt: exhibits logged with case number, sealed condition and forwarding authority recorded.
Storage: malkhana holds sealed exhibits; refrigeration for biological samples.
Internal routing: an exhibit may pass sequentially through several divisions (e.g. a bloodstained knife → Biology → Physics → Fingerprint), each documenting handling.

III. Branches of Forensic Sciences

The scientific disciplines the laboratory draws upon.

A. Scope of the branches

Forensic science is an umbrella term for many parent sciences applied to legal questions.

Forensic Biology & Serology: identifies blood, semen, saliva, hair, and body fluids; species and blood-group determination.
Forensic Chemistry & Toxicology: analyses drugs, poisons, petroleum products, and body fluids for toxic substances.
Forensic Physics / Ballistics: examines firearms, tool marks, glass, paint, and soil.
Forensic Biology–DNA: short-tandem-repeat (STR) profiling for identity.
Questioned Documents: handwriting, forgery, ink and paper examination.
Fingerprint / Dactyloscopy: ridge-pattern identification.
Forensic Anthropology & Odontology: skeletal and dental identification.
Digital / Cyber Forensics: recovery of data from computers and phones.
Forensic Psychology: polygraph, narco-analysis, brain-mapping support.

B. Basis of classification

Branches are grouped by the nature of the evidence they examine.

By material: biological (Biology, DNA) versus physical/chemical (Physics, Chemistry).
By technique: microscopic (hair, fibre), instrumental (GC-MS, spectroscopy), pattern-comparison (fingerprints, ballistics, documents).

IV. Functions of Various Divisions of Forensic Sciences

What each operating division actually does with an exhibit.

A. Purpose of divisional specialisation

Each division isolates one evidence type so expertise and instruments stay concentrated.

Biology & Serology Division: confirms whether a stain is blood (Kastle-Meyer test), determines it is human (precipitin test), and assigns ABO group; examines hair and fibres.
DNA Division: extracts DNA, amplifies loci by PCR, and generates an STR profile matched against a suspect or database; used in paternity and sexual-assault cases.
Chemistry Division: analyses explosives residue, petroleum accelerants in arson, and adulterants; uses gas chromatography and spectrophotometry.
Toxicology Division: detects poisons and drugs in viscera and body fluids; e.g. identifying organophosphate pesticide in a suspected poisoning.
Physics / Ballistics Division: matches a fired bullet to a barrel via striation comparison on a comparison microscope; examines tool marks, glass fracture and soil.
Questioned Documents Division: compares questioned and specimen handwriting, detects erasures under UV/IR, and dates inks.
Fingerprint Division: develops latent prints (ninhydrin, cyanoacrylate fuming) and compares minutiae.
Cyber Forensics Division: images storage media, recovers deleted files, and verifies data with hash values.

B. Instrumental support common to divisions

Divisions share a pool of analytical instruments.

TEXT

GC-MS   : separates and identifies drugs/toxins by mass
FTIR    : identifies compounds by infrared absorption
SEM-EDX : examines gunshot residue particles (Pb, Ba, Sb)
UV-Vis  : quantifies coloured compounds by absorbance

Confirmatory vs. presumptive: presumptive tests (colour reactions) screen quickly; confirmatory instrumental tests establish identity for court.

V. Quality Assurance and Accreditation

How the laboratory guarantees and proves the reliability of its results.

A. Quality assurance (QA) and quality control (QC)

QA is the overall system that ensures results are reproducible and defensible; QC is the day-to-day checking within it.

Standard Operating Procedures (SOPs): every test follows a written, validated method.
Method validation: demonstrating accuracy, precision, sensitivity and specificity before use.
Controls: positive, negative and reagent-blank controls run alongside samples to detect error and contamination.
Calibration: instruments checked against certified reference materials at set intervals.
Proficiency testing: analysts periodically examine blind samples to prove competence.
Documentation & audit trail: raw data, worksheets and instrument logs retained for review.

B. Accreditation

Accreditation is third-party recognition that the laboratory's QA system meets an international standard.

ISO/IEC 17025: the general requirement for testing and calibration laboratory competence.
NABL: in India, the National Accreditation Board for Testing and Calibration Laboratories grants accreditation against ISO/IEC 17025.
Assessment cycle: application → document review → on-site assessment → corrective action → grant → periodic surveillance and re-assessment.
Benefit: accredited results carry weight in court and are recognised across jurisdictions.

VI. Principles and Laws Governing Forensic Sciences

The scientific axioms and the statutes that make evidence usable.

A. Governing scientific principles

A small set of principles justifies every comparison a laboratory makes.

Locard's Exchange Principle: contact between two objects transfers material both ways — the basis of trace evidence.
Principle of Individuality: no two objects are exactly alike (fingerprints, ridge patterns, STR profiles), allowing unique identification.
Principle of Comparison: only like can be compared with like — a questioned sample is judged against a known standard.
Principle of Analysis: results are only as good as the sample, its collection, and its packaging.
Law of Progressive Change: everything changes with time (decomposition, weathering), so evidence must be examined promptly.
Principle of Probability: conclusions are expressed in terms of likelihood, not absolute certainty, especially for class evidence.

B. Statutes and legal framework

Laws determine when scientific findings become admissible evidence.

Indian Evidence provisions: the opinion of an expert is admissible under the expert-opinion rule (Section 45 of the Indian Evidence Act, now mirrored under the Bharatiya Sakshya Adhiniyam, 2023).
Section 293 CrPC / BNSS equivalent: reports of specified government scientific experts may be used as evidence without the expert personally appearing.
Electronic evidence: admissibility of computer output requires a certificate under the electronic-records provision (Section 65B of the Evidence Act).
DNA and bodily samples: collection of samples is supported under the identification-of-prisoners framework and the Criminal Procedure (Identification) Act, 2022.
Court's role: the expert only assists; the judge remains the final arbiter of fact and weighs the opinion against the whole record.

C. Ethical and evidentiary obligations

Legal admissibility rests on the analyst's conduct as much as on technique.

Objectivity: the analyst reports findings for the court, not for the prosecution or defence.
Chain of custody: an unbroken, documented custody record is a legal precondition for admitting an exhibit.
Reproducibility: methods must be transparent enough that another expert could repeat and check them.
Disclosure of limitations: class evidence (blood group, fibre type) narrows possibilities but rarely identifies uniquely, and this limitation must be stated.