FM12.1-6,FM14.{7,19} | Forensic Laboratory, Trace Evidence & Recent Advances — Practice Quiz

Correct. For trace blood stains intended for DNA analysis: swab, air-dry thoroughly (wet swabs develop mould that degrades DNA), and pack in paper (not plastic — plastic traps moisture and causes degradation). Formalin crosslinks DNA and destroys it for analytical purposes. EDTA tubes are for fresh blood from living persons, not dried crime scene stains.

Crime scene biological specimen collection rules: Blood stains → swab, air-dry, paper pack. Fresh blood (living person) → EDTA tube. Viscera → saturated NaCl (formalin NEVER for toxicology/DNA). Semen stains → cut substrate, air-dry, paper pack. All evidence → sealed + labeled + continuous chain of custody.

Formalin preserves tissue morphology but destroys DNA. Plastic airtight bags trap moisture causing mould and DNA degradation. EDTA tubes with refrigeration are for fresh venous blood samples. The correct method for scene stains is swab + air-dry + paper packaging.

Correct. Edmond Locard (1877-1966) formulated the exchange principle: 'Every contact leaves a trace'. When two objects come into contact, material is transferred bidirectionally. The criminal carries away traces from the scene AND leaves traces on the scene. This principle underlies all trace evidence analysis — fibres, glass, paint, pollen, DNA, and fingerprints.

Locard's Exchange Principle: bidirectional transfer at every contact. Types of trace evidence: fibres, glass fragments, paint chips, pollen/botanical, soil, hair, fingerprints, blood/biological fluids, gunshot residue. Transfer efficiency: depends on surface type, contact duration, activity intensity. Primary transfer (direct) vs secondary transfer (indirect) — both considered in casework.

Locard's principle is broader than DNA alone — it applies to all materials (fibres, paint, glass, soil, pollen). Chain of custody is a separate legal principle ensuring evidence integrity. Witness observation is not required by Locard's principle.

Correct. Viscera for chemical/toxicological analysis must be preserved in saturated sodium chloride (NaCl) solution. Formalin crosslinks proteins and interferes with most chemical analytical methods. Ethanol would confound alcohol analysis. EDTA is for blood/DNA samples, not viscera. The standard containers are clean glass jars sealed with sodium salt.

Forensic specimen preservation (viscera): Saturated NaCl — standard for all viscera sent for chemical analysis. Blood for alcohol: NaF (sodium fluoride) + oxalate. Blood for DNA: EDTA. Urine: no preservative or boric acid (bacteriostasis). NEVER formalin for anything requiring chemical/toxicological analysis.

Formalin is the standard histological preservative but destroys toxicological samples. Ethanol interferes with volatile toxin analysis. EDTA is for hematological samples. Saturated NaCl is the universal viscera preservative for forensic chemical analysis.

Correct. Random Match Probability (RMP) is the statistical value that expresses how likely it is that a random unrelated person from the population would share the same STR profile by chance. A typical CODIS 20-locus profile gives RMP values of 1 in 10^20 or less, meaning the profile is essentially unique. This is what courts use to assess the significance of a DNA match.

STR DNA profiling: tandem repeats at multiple loci compared. CODIS (20 loci) gives RMP ~1 in 10^20. Interpretation: inclusion (profile matches), exclusion (profile differs — conclusive), inconclusive (mixed/degraded sample). Forensic report must state: probability of match, population database used, any limitations. India: forensic labs use CODIS-compatible panels.

PCR sensitivity is a technical parameter. The number of loci increases the discriminatory power but RMP is the statistical expression of significance. RFU thresholds determine peak calling but are not the statistical measure used in court.

Correct. Virtopsy (virtual autopsy) using post-mortem CT/MRI provides non-invasive, 3D documentation of skeletal fractures, haemorrhage, gas distribution, and implant positions without altering the body. It is particularly useful for skeletal trauma, mass disasters, and culturally sensitive cases. However, it cannot replace conventional autopsy for histology, tissue sampling, and toxicology — it is complementary.

Virtopsy: post-mortem CT + MRI ± angiography. Advantages: non-invasive, 3D permanent record, no tissue destruction, useful in decomposed/burned/skeletonised remains, mass disasters, cultural/religious concerns. Limitations: cannot assess biochemistry, histology, or toxicology. Future: may become standard pre-autopsy documentation in major trauma centres.

Virtopsy is complementary, not a replacement for conventional autopsy. It cannot detect poisons — toxicology still requires conventional sampling. Chain of custody applies equally to imaging data and physical evidence.

Correct. Digital evidence in India is governed by the Information Technology Act 2000 (IT Act) and, for court proceedings, by the Bharatiya Sakshya Adhiniyam (BSA) 2023 (which replaced the Indian Evidence Act 1872 and modernised provisions for electronic records). Section 63 of BSA (corresponding to old Section 65B IEA) governs admissibility of electronic records. The IT Act addresses cybercrimes, data protection, and digital signatures.

Digital evidence admissibility (India): BSA 2023 Section 63 (= old IEA Section 65B) — electronic records are admissible if accompanied by a certificate from a responsible official confirming authenticity. IT Act 2000 Section 43A: compensation for data security breaches; Section 66: computer-related offences; Section 72: penalty for privacy breach.

The Indian Evidence Act 1872 has been replaced by BSA 2023. CPA 2019 does not govern digital evidence. NMC/MCI regulations govern professional conduct but not the admissibility of digital evidence in court.

Correct. Secretor status is genetically determined (~80% of people are secretors). Secretors have ABO antigens in body fluids (saliva, sweat, semen, vaginal secretions). Blood group O secretors secrete H antigen (since they don't have A or B antigens). Secretor testing on body fluid stains can indicate the blood group of the person who deposited the fluid, which is useful in sexual assault forensics and crime scene investigations.

Secretor status: ~80% secretors (FUT2 gene dominant). Secretors express ABO antigens in saliva, semen, vaginal secretions, tears, sweat. Non-secretors: no ABO antigens in body fluids. Forensic application: saliva/semen swabs can identify blood group and narrow suspect pool. DNA profiling is more discriminatory but secretor status adds corroborating information.

Secretor status is independent of ABO group — it depends on the FUT2 gene. Approximately 80% of people are secretors; the remaining 20% are non-secretors. Rh status does not determine secretor status.

Correct. In a medicolegal report, 'findings' are objective, factual observations (injuries noted, their dimensions, characteristics). The 'opinion' is the examiner's expert interpretation of those findings (e.g., 'consistent with blunt force trauma', 'age of injury 12-24 hours'). The opinion is not binding on the court — it is expert evidence that the court weighs along with other evidence.

Medicolegal report structure: (1) Particulars — name, age, case details; (2) History — as stated to the doctor; (3) Findings — objective, detailed, without interpretation; (4) Opinion — expert interpretation; (5) Signature and date. Expert witness in court: can give opinion evidence; court is not bound; must distinguish fact from opinion in testimony.

Opinions are not summaries of findings — they are interpretive conclusions drawn from findings. Expert opinions are advisory to the court, not binding. Co-signature requirements depend on institutional policy, not legal admissibility criteria.

Correct. Chain of custody documentation allows the court to trace the sample from its collection at the scene through every transfer, storage, and analysis step. A documented, unbroken chain demonstrates that the evidence presented in court is the same evidence collected at the scene and has not been tampered with, contaminated, or substituted. A broken chain undermines evidentiary integrity and can render evidence inadmissible.

Chain of custody elements: (1) collection details (who, where, when, how); (2) packaging and sealing; (3) transfer record for each hand-off; (4) storage conditions and location; (5) analysis log. Break in chain: defence can challenge admissibility. Best practice: sealed evidence bags, tamper-evident labels, written transfer receipts.

Temperature tracking is part of storage conditions but not the primary reason for chain of custody. Analyst qualifications are documented separately. ISO 17025 is a quality standard for laboratories but chain of custody is a legal evidentiary requirement, not just an accreditation requirement.

Correct. Selvi v State of Karnataka (2010) — the Supreme Court held that P300/BEAP, polygraph, and narcoanalysis results are NOT admissible as evidence (violate Art 20(3) + Art 21). However, the Court also held that physical discoveries made as a consequence of voluntarily given information during such tests (e.g., 'I buried the weapon at X' leading to discovery of the weapon) may be used as circumstantial evidence under Section 27 Indian Evidence Act (now BSA Section 25).

Selvi 2010 summary: Polygraph + Narcoanalysis + BEAP/P300 = inadmissible as evidence (Art 20(3) + Art 21). Physical discoveries from voluntarily disclosed information during the procedure = potentially admissible as circumstantial evidence (BSA Section 25). DNA, blood alcohol, breath alcohol = permissible (don't violate mental privacy).

BEAP results are inadmissible in both civil and criminal proceedings. Voluntary consent does not make them admissible — Selvi is absolute on this. Witness corroboration cannot rescue inadmissible evidence. Only consequential physical discoveries are usable.

Correct. In mixed DNA profiles from sexual assault cases, differential extraction separates sperm cells from epithelial cells by exploiting the resistance of sperm heads to detergent lysis (differential lysis technique). The sperm fraction then undergoes Y-chromosome STR profiling (male contributor) separately from the autosomal STR profile of the epithelial fraction (victim). This separation is fundamental to SARC (Sexual Assault Referral Centre) forensic protocol.

Sexual assault forensic protocol: (1) time since assault (affects sample quality); (2) differential extraction — sperm fraction vs epithelial fraction; (3) Y-STR for male contributor from mixed profiles; (4) autosomal STR for victim; (5) sample types: vaginal swab, oral, anal, clothing. Time window: sperm viable 3-7 days vaginally; DNA degrades faster with washing.

Rh grouping does not differentiate profiles in a mixed sample. Mitochondrial DNA is useful for hair/skeletal remains but less informative for sexual assault mixed profiles. Precipitin test detects human blood, not useful for sperm/epithelial cell differentiation.

Correct. IT Act Section 43A (inserted by 2008 amendment) imposes a civil liability on 'body corporates' (including hospitals) that handle sensitive personal data and fail to implement 'reasonable security practices'. In case of negligent data security causing wrongful loss, the body corporate must pay compensation. The SPDI (Sensitive Personal Data and Information) Rules 2011 under Section 43A specifically include health records.

IT Act 2000 (amended 2008) healthcare relevance: Section 43A: hospital liable for sensitive personal data breach (civil compensation); SPDI Rules 2011: health records are sensitive personal data; Section 72A: disclosure of information in breach of lawful contract = criminal offence; Section 66C: identity theft. Hospitals must: implement IS/IEC 27001 or equivalent, conduct risk assessments, have incident response policies.

Section 66 (hacking) addresses criminal liability of the attacker, not the hospital's failure to protect data. Section 72 relates to certifying authorities (digital signatures). CPA 2019 could also apply but Section 43A specifically addresses the hospital's data security obligation.