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

Correct. Each distinct specimen must be: (1) photographed in situ, (2) collected with appropriate technique, (3) separately packaged to prevent cross-contamination between samples, (4) sealed with tamper-evident labels, and (5) individually documented in the chain of custody log at the time of collection. Mixing samples destroys their individual evidentiary value.

Scene of crime protocol: (1) secure the scene; (2) photograph before touching; (3) collect in priority order (most fragile/perishable first); (4) separate packaging for each specimen; (5) seal, label (description, location, date, time, collector); (6) chain of custody log entry before leaving scene. Contamination between samples = inadmissible confusion in lab analysis.

Pooling specimens is the worst possible approach — it destroys the evidentiary integrity of each individual specimen. Photography preserves documentation but does not replace physical collection of trace evidence. All evidence must be physically collected and documented. The forensic examiner should personally supervise or perform collection.

Correct. Post-mortem redistribution causes alcohol (and many drugs) to diffuse from the stomach and liver into the central blood compartment, artificially elevating central blood concentrations. Femoral vein blood is the accepted standard for post-mortem blood alcohol because it is most distant from gastrointestinal sources and shows least redistribution. Vitreous humour is also used as a confirmatory sample — it correlates well with ante-mortem blood alcohol but is used as supplementary evidence.

Post-mortem alcohol sampling: primary = femoral vein blood (with NaF preservative); confirmatory = vitreous humour (correlates 1:1 with blood at equilibrium, unaffected by redistribution). Post-mortem redistribution: alcohol, many drugs (opioids, sedatives) move from GI tract/liver → central blood post-mortem. Always state sampling site in forensic report.

Heart blood is the WORST site for post-mortem alcohol — it is adjacent to the stomach and severely affected by redistribution. Vitreous humour is useful but is a supplementary sample, not the primary one. Urine gives historical exposure (not acute BAC) and is affected by decomposition.

Correct. Mitochondrial DNA (mtDNA) has two advantages for degraded/old samples: (1) each cell contains hundreds to thousands of mitochondria (vs. 2 copies of nuclear DNA), so more copies survive degradation; (2) maternal inheritance means mtDNA from a maternal relative (e.g., the deceased's mother, maternal sibling) can be used as a reference even if no direct sample from the deceased exists. This makes mtDNA ideal for skeletal, dental, and hair shaft analysis.

Nuclear STR vs mtDNA: Nuclear STR = high discrimination, paternal and maternal origin, distinguishes individuals including siblings. mtDNA = low discrimination, maternal lineage only, cannot distinguish maternal relatives, but survives in old/degraded samples (bone, teeth, hair shaft). Use mtDNA when nuclear DNA is too degraded. Always report mtDNA as 'cannot exclude' not 'matches'.

mtDNA has LOW discriminatory power (limited hypervariable region sequences) compared to nuclear STR (billions of possible combinations). mtDNA cannot distinguish identical twins AND it cannot distinguish maternally related individuals — the opposite of what makes nuclear STR powerful. Rapid results are not an advantage of mtDNA.

Correct. An expert witness's primary duty is to the court (not the party who called them) and they must only opine within their stated area of expertise. It is professionally and legally appropriate to say: 'That question falls outside my area of forensic medical expertise; I am not in a position to provide a reliable opinion on that matter.' Speculating outside expertise can mislead the court and expose the expert to criticism.

Expert witness duties: (1) duty to the court, not the calling party; (2) opinion within area of expertise only; (3) objective, impartial, and not an advocate; (4) acknowledge uncertainty and limitations; (5) never speculate; (6) must be able to defend opinion under cross-examination. Key Indian case: Ramesh Chandra Agrawal v Regency Hospital (2010) SC — expert witnesses must give objective evidence.

Contempt of court requires wilful disobedience of a court order — declining to opine outside expertise is not contempt. Asking the judge to dismiss a question is the lawyer's role, not the expert's. Agreeing with a question formulated by the defence is a serious professional error.

Correct. A proper EMR system maintains an immutable audit trail (access log) that records: who accessed the record, when, what was viewed or changed, and any modification with before/after values. This log is typically stored separately from the main record and cannot be altered without detection. It is the primary technical evidence of document integrity in disputes about record tampering.

EMR integrity features: (1) immutable audit trail; (2) digital signature/hash of entries; (3) date/time stamping from a trusted time source; (4) access controls and user authentication; (5) disaster recovery backups. Under BSA Section 63 (old IEA 65B): electronic records admissible with certificate from responsible official. Altered EMR: audit trail mismatch → admissibility challenge → potentially fabrication charge.

Printed copies can themselves be fabricated. Notarised affidavits cannot certify digital integrity. Backup copies show the content at a point in time but do not by themselves prove the original was not tampered with between backups. The audit trail is the definitive integrity tool.

Correct. Blood group O requires genotype OO (two recessive O alleles). Father with blood group A may have genotype AO (heterozygous). Mother with group B may have genotype BO (heterozygous). AO × BO can produce OO offspring with a 1 in 4 probability. This means the putative father CANNOT be excluded based on blood group alone.

ABO blood group genetics: A = AA or AO; B = BB or BO; AB = AB; O = OO. Forensic application: blood groups can EXCLUDE paternity (if child has allele neither parent can provide) but cannot CONFIRM paternity (too common). DNA profiling is the standard for positive paternity establishment. Always state 'cannot exclude' or 'excluded' — never 'proven'.

If the father were AA (homozygous), he could not pass an O allele — the child could not be OO. If the mother is BB, she cannot pass an O allele. Blood group O cannot be born from parents who are both homozygous dominant. Mutation is an extremely rare explanation and is not invoked in routine casework.

Correct. When samples are stored unsealed in close proximity, cross-contamination is a realistic possibility. If the crime scene sample was contaminated with the reference sample (or vice versa), an apparent match could be an artefact of laboratory contamination rather than evidence of the suspect's presence at the scene. The result must be declared inconclusive and the matter referred to quality assurance review.

Chain of custody + contamination control are inseparable. Laboratory contamination sources: aerosol during opening, direct contact, analyst's DNA (eliminated by staff elimination database), reagent contamination. Standard lab practice: negative controls in every batch, separate pre- and post-PCR areas, staff DNA database for exclusion, sealed evidence until bench work. Contamination = chain of custody failure = inadmissibility challenge.

A match under contamination risk conditions is not confirmatory evidence. DNA can migrate between open containers via aerosol or direct contact. Repeat testing of contaminated samples only replicates the contamination — it does not validate the original result.

Correct. GC-MS provides both separation (gas chromatography) and structural identification (mass spectrometry — molecular fragmentation pattern = fingerprint). LC-MS/MS is preferred for polar/non-volatile compounds. Both techniques provide confirmatory (not just presumptive) identification because mass spectra are compound-specific and can be matched to reference spectral libraries. ELISA and TLC are screening tests only — positive results must be confirmed by GC-MS or LC-MS/MS before medicolegal reporting.

Forensic toxicology two-step approach: (1) Screening: immunoassay (ELISA/RIA) or TLC — fast, sensitive, some false positives; (2) Confirmation: GC-MS or LC-MS/MS — specific, definitive, court-acceptable. Both methods must be applied before forensic reporting. GC-MS: separates volatile compounds; LC-MS/MS: preferred for drugs of abuse, opioids, polar metabolites. Chain of custody applies equally to toxicological specimens.

ELISA is an excellent screening test but has cross-reactivity and cannot provide the compound-specific structural information needed for confirmation. TLC is a screening technique. HPLC separates but without MS detection cannot confirm molecular identity with the certainty required for forensic reporting.

Correct. Microscopic morphological comparison of hair characteristics (medulla pattern, cuticle scale, pigmentation distribution) was once used forensically but has been shown by NIST studies (2009) and FBI reviews to be scientifically unreliable for positive identification. Several wrongful convictions were linked to misleading microscopic hair comparisons. It is now considered a presumptive tool only. Nuclear STR from root cells and mtDNA from shaft are the scientifically valid approaches.

Hair evidence: nuclear DNA (root cells) = best for identification; mtDNA (shaft) = useful when root absent, identifies maternal lineage; morphological microscopy = NOT reliable for positive ID (NIST 2009); toxicology (hair shaft segmental analysis) = chronic drug exposure history (~1 cm = 1 month). NB: FBI 2015 review found microscopic hair comparison overstated in hundreds of cases.

mtDNA analysis of the hair shaft is valid forensically (maternal lineage). Nuclear DNA from root with follicular material is the best identification method. Toxicological hair analysis for drug history is a validated technique. Microscopic morphological comparison is the LEAST reliable of these options.

Correct. EDTA (ethylenediaminetetraacetic acid) is the anticoagulant of choice for DNA analysis. It chelates divalent cations (Mg²⁺, Ca²⁺) required by DNases, thereby inhibiting DNA degradation. EDTA anticoagulated whole blood preserves white cell nuclear DNA for extraction. Sample is stored at 4°C or -20°C for longer storage.

Blood collection tubes for forensic purposes: EDTA (purple) = DNA analysis; NaF/oxalate (grey) = blood alcohol estimation; Plain (red) = serology/grouping; Heparin (green) = NEVER for DNA (PCR inhibitor). Volume: 2-5 mL for DNA; must be labeled with name, date, collector; cold chain maintained.

Plain tube (serum) has no anticoagulant — DNA degradation begins quickly after clotting. Fluoride-oxalate tubes are for blood glucose/alcohol estimation; fluoride is inhibitory to some DNA enzymes. Heparin interferes with PCR amplification and is NOT suitable for DNA analysis.