Physical Evidence: Nature, Types, Collection and Chain of Custody

Physical evidence is any tangible material recovered from a scene, a victim or a suspect that can clarify a fact in issue through scientific examination. Paul L. Kirk called it the "mute witness" that does not forget, does not get confused, does not get intimidated and does not lie, in contrast to eyewitness testimony, which Indian appellate jurisprudence treats as inherently fallible. The Supreme Court reaffirmed this preference in State of Maharashtra v. Damu (2000)where circumstantial physical evidence (recovery of the victim's belongings under Section 27 of the Indian Evidence Act, now BSA 2023 Section 23) tied the chain together, and in Mukesh v. State (NCT of Delhi) (2017)the Nirbhaya appeal, where DNA, dental and bitemark evidence carried weight that no single eyewitness account could.

The scientific bedrock isEdmond Locard's exchange principle, formally articulated in his 1920 work L'Enquête criminelle et les méthodes scientifiques at the Lyon police laboratory (established 1910): "every contact leaves a trace". When a suspect touches a victim, fibres, hair, skin cells, sweat, saliva, blood, soil, paint, glass fragments and gunshot residue move in both directions. The principle is the reason a forensic examiner collects control samples, reference samples and the substrate alongside the questioned stain, and the reason an integrated CSI kit (as supplied by the Directorate of Forensic Science Services DFSS, New Delhi, to State SFSLs) carries swabs, tweezers, tape lifts and sterile containers for each transfer class. The Indian CSI doctrine adds three working corollaries: physical evidence is created at the moment of contactdegraded by every subsequent action(weather, footfall, well-meaning bystanders), and only as good as its documentation.

Physical evidence is classified along three axes, and the correct interpretation of any specific item depends on which axis is being applied.

Axis 1, evidential value.Individual characteristics allow association with a single source: fingerprint minutiae (ridge endings, bifurcations), DNA STR profile across the CODIS-style 13 to 20 loci panel used by the CFSL DNA division and CDFD Hyderabad striations on a fired bullet from a single barrel, handwriting from a single writer, and tool-mark striations on a single tool edge.Class characteristics allow categorisation only: ABO blood group, shoe brand and size, paint colour and resin type, fibre polymer (cotton, polyester, nylon), glass refractive index, fired-cartridge calibre. Class evidence narrows the suspect pool; individual evidence identifies the source.

Axis 2, behaviour at the scene.Transient evidence is short-lived (odour of phosphine, ambient temperature, blood that dries from glossy to matt, ice melt around a body) and must be documented first or it is lost.Conditional evidence captures the event state (door bolt position, headlight switch state in a road-traffic-accident vehicle, lividity pattern on a body before it is shifted).Pattern evidence is geometric (bloodstain spatter direction, glass radial and concentric fracture, gunshot-residue tattoo and powder distribution, tyre mark spacing, tool-mark impression shape).Transfer evidence is the direct Locard product (hair, fibre, paint, glass, soil, body fluid, gunshot residue on hands).

Axis 3, nature of the material.Biological evidence covers blood, semen, saliva, hair, bone, viscera, tissue, urine, faeces, nails and the bacterial-toxin / botulinum / Vibrio cholerae specimens forwarded to the Microbial Toxicology Division at CFSL Hyderabad.Chemical evidence covers drugs and poisons (NDPS exhibits, pesticides, heavy metals, alcohol, arson accelerants, explosives, dyes, inks).Physical evidence in the narrow sense covers fingerprints, footwear and tyre impressions, tool marks, firearms and cartridge cases, glass and paint fragments, fibres, and questioned documents. NCRB's Crime and Criminal Tracking Network and Systems (CCTNS)uses these categories to index seized exhibits across States.

Five search patterns are standard in forensic scene examination. The choice depends on the size of the scene, the number of searchers and the terrain.

Spiral search. A single searcher walks in a spiral from a fixed point.Spiral inward starts at the perimeter and converges on a centre target (typically the body in a homicide).Spiral outward starts at the centre and works outward to the perimeter. Inward spiral preserves the centre, outward spiral preserves the perimeter; both fail in cluttered indoor scenes. Best for small open scenes or the scene under a body once the body is moved.

Grid search. Two passes at right angles: first a strip search north-south, then the same area re-searched east-west. Slow but the most thorough; finds the second-pass evidence the first pass missed. Standard for outdoor scenes where time allows, for example open-field homicide and aircraft-crash debris recovery as performed by DGCA / AAIB alongside the State SFSL.

Strip or lane search. The scene is divided into parallel strips; searchers walk each strip in turn. Faster than grid (single pass) but misses what a perpendicular pass would catch. Used for railway-track scenes, road verges, and the perimeter of an explosion site coordinated by the NSG Bomb Data Centre and the NIA.

Zone or quadrant search. The scene is divided into zones (rooms in a house, quadrants in a hall), and a searcher or team is assigned per zone. Standard indoor method, used by Delhi Police Crime Branch in flat and apartment scenes and by State SFSL mobile units sent under BNSS 2023 Section 176(3).

Wheel or ray search. A small circular scene is searched along rays radiating from a centre. Limited utility because spacing widens away from the centre; used mainly for clearly circular scenes (a single bomb crater).

A sixth pattern, the link search is taught in some Indian curricula: the investigator follows logical connections between items (body, weapon, point of entry) rather than a geometric pattern. It is more a state of mind than a method.

Collection rules are evidence-class-specific; the operational details determine whether a sample survives analysis.

Biological evidence (blood, semen, saliva, hair, tissue). Wet stains are dried at room temperature, away from direct sunlight and heat, then packed in paper bags or breathable cotton cloth never plastic. Plastic traps moisture, encourages bacterial and fungal growth, and destroys DNA within hours. Liquid blood for grouping and DNA is drawn into an EDTA vacutainer(purple cap, 5 ml) and refrigerated at 4 degrees Celsius; for alcohol estimation, sodium fluoride and potassium oxalate(grey cap) is used to prevent fermentation. Swabs of dried stains are taken with sterile distilled-water-moistened cotton swabs, air-dried, and placed in paper sleeves. Hair is collected with clean tweezers (root preserved for nuclear DNA, shaft for mitochondrial DNA at CDFD Hyderabad) and packed in folded paper bindles inside paper envelopes. A control sample of unstained substrate is always taken from the same surface.

Viscera for toxicology. Stomach with contents, small intestine first 30 cm with contents, half each of liver and kidney, blood, urine, and where relevant brain, lung and skin around an injection mark, are placed in wide-mouthed glass jars with saturated common salt (sodium chloride) as preservative except blood (NaF or sodium fluoride) and the specimen for alcohol (NaF). Each jar is sealed, labelled, and forwarded with Form 21 to the FSL toxicology division. Where insecticide poisoning is suspected, rectified spirit must not be used because it interferes with the analysis.

Chemical evidence. Suspected drugs under the NDPS Act are weighed, sampled (representative portions per the standing instruction of the Narcotics Control Bureau), packed in heat-sealed polythene with a moisture-resistant outer wrap, sealed with the seizing officer's seal, and forwarded with the NDPS forwarding memo. Arson debris is packed in clean unused metal paint cans or nylon evidence bags never plastic zip bags, to retain volatile accelerant vapours for headspace GC-MS.

Glass and firearms. Glass fragments are packed in rigid cardboard boxes with cotton padding edges separated, to preserve fracture edges for jigsaw fits. Each fragment is bagged individually if small.Firearms are never packed loaded the magazine is removed, the chamber cleared, the weapon is held at the chequered grip and trigger guard to preserve fingerprints, and packed in a rigid box with cable ties through the trigger guard.Live cartridges and fired cartridges are packed separately in cotton-padded boxes.

Fingerprints and impressions. Latent prints on portable items are submitted with the item, packed to avoid contact with the print surface. Latent prints on immovable surfaces are lifted with black powder + transparent lifting tape onto a backing card for dark prints on light surfaces, white powder for light prints on dark surfaces, magnetic powder for plastic and leather. Footwear impressions in dust are lifted with electrostatic dust lifters and in soil with dental stone casts(preferred over plaster of Paris because dental stone is harder, cures faster and captures finer detail).

Tool marks and questioned documents. Tool marks are photographed in oblique light, then cast in silicone rubber or polyvinylsiloxane. Documents are handled with cotton gloves, placed flat between two sheets of acid-free paper inside a rigid folder, and never folded across writing or stapled.

The Indian context anchor: every State Mobile Forensic Unit under the DFSS Centrally Sponsored Scheme carries a standard CSI kit with these collection items, and the BNSS 2023 Section 176(3)makes the FSL visit to the scene of every offence punishable with seven years or more imprisonment mandatory.

Packaging is a legal act, not a logistical one. Each exhibit is packed in its own container, the container is closed, the closure is sealed with the seizing officer's brass seal in molten wax or a numbered tamper-evident security tag, and the seal impression is recorded on the seizure memo, the panchnama and the forwarding memo. A duplicate seal impression on a separate paper accompanies the parcel so the FSL can verify the seal is intact and matches the impression.

The BNSS 2023 Section 105 requires audio-video recording of the search and seizure on any electronic device available to the police, with copies preserved for the Magistrate and the accused. This is the statutory upgrade over the old CrPC Section 100 and brings the search itself into the chain-of-custody record.BNSS 2023 Section 176(3)mandates an FSL visit for offences carrying seven years' imprisonment or more, with the seizure now reflected in the FSL examination report attached to the chargesheet.BNSS 2023 Section 348 carries forward the IEA Section 73 power, allowing the court to direct the accused to give specimens of handwriting, signature, finger impressions or voice for comparison.

The forwarding memo carries the FIR number, the case sections, the list of exhibits with seal numbers, the examination sought (DNA profiling, narcotics identification, toxicology, ballistics, fingerprint comparison, document examination), the laboratory addressed (CFSL Hyderabad for narcotics, DNA and toxicology; CFSL Chandigarh for ballistics and questioned documents; CFSL Kolkata for chemistry and serology; CFSL Pune for general chemistry and biology; CFSL New Delhi as the apex coordinating laboratory; CFSL Bhopal, Guwahati under DFSS expansion; the appropriate State SFSL for first-line work;RFSL for regional support), and the despatch mode (registered post, special messenger, sealed despatch).

Indian institutional anchor: the Directorate of Forensic Science Services(DFSS) under the Ministry of Home Affairs administers the central CFSL network and issues the Quality Manual that State SFSLs follow. The National Institute of Criminology and Forensic Science(now LNJN NICFS Rohini, Delhi) trains police and forensic officers on these packaging and forwarding protocols. NABL accreditation under ISO/IEC 17025 is now mandatory for CFSLs and many SFSLs and explicitly requires documented chain-of-custody and tamper-evident packaging.

Chain of custody is the unbroken paper trail showing every person who held the exhibit from the moment of seizure to its production in court. At each transfer, the record names the person handing over, the person receiving, the date and time, the location, the purpose of the transfer, the seal status, and the signature of both parties. The minimum nodes for a typical exhibit are:seizing officer at the sceneinvestigating officerstation house Malkhana with Malkhana register entrydespatcher to the FSLFSL receipt clerkanalystreturn to despatchreturn to policeproduction in court. Each node is a row in the register; gaps are fatal.

The Bharatiya Sakshya Adhiniyam 2023 frames the chain in three statutory provisions.Section 22(relevancy of facts forming part of the same transaction) puts the chain of seizure within the res gestae of the offence.Section 39(opinion of experts) makes the FSL report admissible only if the chain is intact, because the expert's opinion presupposes that the sample examined is the sample seized.Sections 56 to 63 govern electronic records: Section 56 makes electronic records primary evidence in the form printed, Section 61 prevents denial of admissibility solely because the record is electronic, and Section 63(carrying forward IEA Section 65B) requires the electronic-evidence certificate for any computer-generated output, including the videographed search under BNSS Section 105 and the FSL's analytical output (LC-MS chromatograms, DNA electropherograms, fingerprint AFIS hit lists).

Indian appellate jurisprudence on broken chains is rich. In State of Maharashtra v. Damu (2000)the Supreme Court accepted a chain that was carefully documented across multiple seizing officers and the Malkhana. In Anvar P.V. v. P.K. Basheer (2014)and Arjun Panditrao Khotkar v. Kailash Kushanrao Gorantyal (2020)the Court held that the Section 65B certificate(now BSA 2023 Section 63 certificate) is mandatory for any secondary electronic record, a holding that now applies to CCTV footage from a scene, mobile-phone extractions and FSL instrument printouts. In Tomaso Bruno v. State of UP (2015)the Court treated the failure to produce contemporaneous CCTV from the hotel as adverse to the prosecution, a chain-of-custody point dressed in adverse-inference clothing. In Mukesh v. State (NCT of Delhi) (2017)the Nirbhaya appeal, the defence attack on the DNA evidence focused squarely on chain integrity between the SHO, the autopsy surgeon, the AIIMS sample storage and the CFSL Rohini DNA division; the Court found the chain intact and upheld convictions.Selvi v. State of Karnataka (2010)sits adjacent to the chain framework by holding that polygraph, narco and brain-mapping results obtained without consent are inadmissible regardless of their analytical accuracy, a reminder that the chain begins with a lawful seizure or sampling, not with the laboratory door.

Common chain-of-custody failures include: missing Malkhana entry, broken seal at the FSL, mismatch between the seal impression on the despatch memo and the seal on the parcel, gap in dates between despatch and FSL receipt, absence of the BSA Section 63 certificate for electronic outputs, and a chain that ends at the analyst without the return-to-court signature.