Investigation of Explosion and Arson Cases

Both arson and bomb-blast scenes sit inside the same procedural envelope. Arson is charged under Bharatiya Nyaya Sanhita Sections 324 to 326 (mischief by fire, with imprisonment scaling up to ten years for life-threatening or dwelling fires). Bomb attacks are charged under the Explosive Substances Act 1908 (Sections 3 to 5), often read with the Unlawful Activities (Prevention) Act 1971 when terror motive is present, and with sections of the BNS for the resulting deaths and injuries. Because every one of these carries seven years or more, BNSS Section 176(3)makes a forensic-team visit mandatory. The first lawful act on arrival is not collection. It is documentation and cordon.

First-responder priorities at both scene types follow the same three-letter discipline.

1. Rescue. Life safety first. Fire suppression, casualty extraction, primary medical triage. At explosion scenes a dedicated secondary-device search is run before any forensic work begins, because a second bomb timed for first responders is a documented terrorist tactic from the 1993 Mumbai serial blasts onwards.
2. Preserve. Inner perimeter for forensic personnel only; outer perimeter for crowd, press and uniformed support. Both perimeters are recorded with time-stamped photographs before anything is touched or moved. Panch witnesses are called for the seizure memo.
3. Command. A single Incident Commander signs every entry log, every evidence label, and every dispatch document. This is what survives cross-examination under BSA Section 39when the analyst is on the stand months later.

Life safety is always the first priority.

The post-blast scene is read outward from a single point. That point is the seat of explosion identified by the convergence of three observables: the deepest crater (or for a vehicle bomb, the maximum metal deformation), the geometric centre of fragment dispersal, and the radial blast-pattern lines on adjacent walls and ground. Locating it correctly is the single most important act of the entire investigation; everything downstream (charge estimation, witness-account reconciliation, fragment quadrant labels) keys off this origin.

Once the seat is fixed, the investigator measures the crater. Diameter, depth and the direction of soil or floor-slab ejecta are recorded with scale and ABFO ruler.Hopkinson-Cranz scaling then back-calculates an approximate TNT-equivalent charge weight, which constrains the suspect explosive (low or high, primary or secondary, military or improvised).

Damage radiates outward in three over-pressure zones. The boundaries are not exact metres; they are pressure-defined and must be inferred from structural damage.

The scene is then divided into a quadrant grid centred on the seat. Each quadrant is searched systematically using grid and zone search techniquesby trained SOCO personnel. Metal detector and rare-earth magnet sweep up ferrous fragments: nuts, bolts, ball bearings, casing pieces, circuit fragments, timer remains, battery casings, wire bundles with colour-coded insulation. UV alternate-light catches trace organic residues; portable Ion Mobility Spectrometry (IMS) screens swabs from crater walls and casing fragments at the scene itself for nitroaromatics (TNT), nitrate esters (PETN, NG) and RDX. The post-blast residue chemistry workflowtakes over once samples reach the lab.

Witness interviews at this stage carry hard forensic value, not just narrative value. Trained investigators ask for specific cues: pressure-pattern (single bang versus sequential thuds, the latter hinting at multiple devices as in the 1993 Mumbai serial pattern), smoke colour (white tends to indicate low explosive or pyrotechnic mixtures, black indicates fuel-rich detonation), and smell. Almond smell points to cyanogen-laced devices, sulphur to low explosives, sweet petroleum-like odour to nitroaromatics. These are corroborative, never standalone, but they direct the chemistry.

Arson scenes are read inward, not outward. The investigator works from the perimeter of fire damage toward the area of greatest charring, looking for the point of origin. The full NFPA 921 systematic methodology for cause-and-origin work is covered in the related topic on fire and arson investigation: cause, origin and burn patternsat order 2 of this unit, and the book chapter on fire and burn pattern interpretationcarries the detailed treatment. retain the headline indicators: V-patterns widening upward from a single low point indicate natural growth; multiple low V-patterns, low burns running along the floor between rooms, and pour patterns on horizontal surfaces all point toward incendiary origin with an accelerant.

Each suspected pour area is photographed with scale before any disturbance.Sampling then collects char plus concrete substrate plus carpet plus underlying wood from the same square, into a single container, because volatile accelerant residues partition between substrate types and the lab needs all of them for passive headspace SPME-GC-MSwork-up. A control sample from a visually clean adjacent area is collected in a separate container, labelled as control, and submitted to the same lab in the same run. Without a paired control, defence counsel will argue the residue came from cleaning fluids, polish, or background contamination.

Documentation extends beyond the burn area. Ambient temperature, wind direction, ventilation state (doors open or closed, HVAC running), and weather conditions are logged because all four affect fire dynamics and volatile-residue preservation. Time of fire-service arrival, hose-stream entry points, and overhaul activity are noted, because firefighting itself moves and dilutes evidence.

Major Indian explosion and arson investigations fan out across a stack of agencies with non-overlapping mandates. Each agency has a defined, non-overlapping mandate.

• State Bomb Disposal Squad (BDS). First on scene for any suspect or unexploded device. Renders safe (water-jet disruptor, manual disarm, or controlled detonation). Hands the residue and any recovered components to the forensic team.
• National Security Guard (NSG) Special Action Group plus Bomb Squad. First call for major terrorist devices, VVIP threats, and complex IEDs requiring specialised technical render-safe. NSG bomb data centre maintains a national device-pattern database that informs attribution.
• National Investigation Agency (NIA). Statutory investigating agency for terrorism cases under UAPA. Takes over from state police on declaration of NIA jurisdiction. Coordinates forensic submission and prosecution.
• CFSL Hyderabad. Designated central lab for post-blast residue analysis and arson fire-debris analytical work. Houses GC-MS, LC-MS, IMS and Raman instrumentation for explosive identification.
• CFSL Chandigarh. Second post-blast analytical centre, particularly for cases originating in northern and western India.
• State SFSL fire-debris and explosives divisions. Handle routine arson and small-bomb casework; major cases are referred up.
• BPR&D (Bureau of Police Research and Development). Issues SOPs and runs training programmes for state police bomb-disposal personnel and SOCO teams.

Every transfer between hands is logged on a chain-of-custody form. Seizure of evidence at the scene happens in front of panch witnesses(independent local witnesses, typically two), whose signatures appear on the seizure memo. Containers are sealed with lacquer or tamper-evident tape, labelled with case number, date, time, location, collector name and panch witness names, and dispatched to the assigned lab through a documented courier line. The full ledger is admissible under BSA 2023 Section 39and any gap in the chain is the easiest single line of attack for the defence.

The SOCO mobile lab and field kit inventorycovers the standard tools deployed: metal detectors, IMS units, paint cans, nylon pouches, swab kits, evidence flags and the Bureau of Indian Standards photography rig.

Death investigation runs in parallel with scene work, and the autopsy findings constrain the scene interpretation. Bodies recovered from an explosion show characteristic blast injuries: blast-lung from over-pressure (alveolar haemorrhage, pneumothorax), tympanic-membrane rupture (a sensitive marker for shock exposure even when external injury is minimal), fragmentation wounds from primary and secondary fragments, and traumatic amputation when the victim was close to the seat. Fire deaths show charring, pugilistic posture, and biochemical evidence of inhalation injury. Carboxyhaemoglobin and cyanide quantification on heart-blood samples distinguish ante-mortem from post-mortem fire exposure; this is the toxicology bridge into gases and volatile poisons: CO, cyanide and alcoholswhere the analytical chemistry of CO and HCN is covered for the forensic-toxicology bullet.

Key Indian cases illustrating investigation methodology:

• Bombay 1993 serial blasts. RDX-based vehicle and tiffin bombs across twelve sites; the methodological template for post-blast quadrant searches in Indian metros.
• Bombay Stock Exchange 1993 and Delhi serial blasts 2008.Vehicle-borne and motorcycle-borne devices; investigation models for multi-site coordination.
• Mumbai 7/11 train blasts 2006 and 26/11 attacks 2008.Pressure-cooker and grenade devices, then assault rifles; redefined NSG and NIA coordination after the Multi-Agency Centre reforms.
• Pulwama 2019.VBIED against a CRPF convoy; the post-blast analysis identified an ammonium-nitrate-based main charge, demonstrating the role of trace residue chemistry in attribution.
• Uphaar cinema fire Delhi 1997.Transformer-room electrical fault plus blocked exits; the Indian case study for arson-versus-accidental investigation and the building-safety angle.
• Kumbakonam school fire 2004.Thatched-roof kitchen fire that killed 94 schoolchildren; led to revised fire-safety norms for schools.
• AMRI Hospital fire Kolkata 2011.Basement storage fire; institutional failure of fire-safety compliance, prosecuted as culpable negligence.
• Surat coaching-centre fire 2019.Takshashila Arcade building rooftop coaching; ground-floor electrical short circuit combined with single-staircase egress.