Crime Scene Investigation Tools, Kits and the Mobile Laboratory

Indian forensic practice runs the kit chain through four tiers, and the tier that responds depends on the seriousness of the offence and how quickly the scene needs handling. The hierarchy is not academic. It maps directly to who's authorised to do what at the scene, what evidence stays at the scene for the next tier, and what gets shipped onward.

The capability grows at each tier, but the discipline at every tier is the same: nothing leaves a tier in a state worse than it arrived. Tier 1 holds the scene without contaminating it. Tier 2 recognises and lifts without destroying. Tier 3 produces a sealed packet that survives transit. Tier 4 opens the packet, runs the confirmatory test, and signs the report. The chain of custody you read about in Chain of Custody is what stitches the tiers together.

The basic field kit is the minimum toolset every police patrol vehicle in India is required to carry. Its function is to hold the scene without contaminating it until the IO and SOCO arrive. An officer who enters the scene without PPE can compromise more evidence than any reagent will recover.

Contents worth knowing cold:

• Personal protective equipment. Nitrile gloves (multiple pairs, multiple sizes), surgical masks, shoe covers, hair caps. Indian state SOPs require fresh gloves between every item handled.
• Torch and a high-power LED hand-lamp. Most scenes are processed under poor lighting; a 1000-lumen LED is now standard.
• Sealed packet bags in three sizes (small for swabs, medium for clothing, large for bulkier items) plus a roll of wax thread and a sealing wax stick. Security tape is the modern alternative.
• Cotton swabs and sterile distilled water vials for wet-and-dry biological swabbing.
• A measuring tape (5 m and 50 m). The 50 m tape is for outdoor scenes; the 5 m for indoor and item-to-landmark dimensions.
• A pocket-size camera or a smartphone in a forensic case-management app. Most state forces now issue 5G-enabled tablets running CCTNS modules.
• A pad of barricade tape and a few traffic cones to extend the cordon described in Securing and Documenting the Crime Scene.
• A notebook and pen (in working ink, in 2026 still important because pencils smudge and digital devices fail).

The entire kit fits in a single field bag and costs a few thousand rupees in total. Its value is in being present, fully stocked, and correctly used.

The investigator's kit is the SOCO-level kit. It adds the tools needed to recognise less-obvious evidence (latent prints, biological stains under ALS, trace fibres), to conduct presumptive tests on the spot, and to lift impression evidence that won't survive transit. Most district-headquarters SOCO units carry a standardised kit issued by the state FSL.

Field notes on kit use:

• The ALS unit is the single most expensive item in the kit (typically ₹40,000 to ₹2,00,000 for a multi-wavelength unit), and it's the item most often left behind because of weight. Don't.
• Presumptive reagents have shelf lives. Most state SOPs require a fresh batch every six months, with the date stamped on each vial. An expired Kastle-Meyer can produce a false negative that misses a wiped-down blood scene.
• Magnetic powder is gentler on porous surfaces (untreated wood, leather) than standard powders. This is often missed because most kit lists treat all powders as one item.
• The casting frame for plaster work is often improvised from a plastic strip; the kit's frame is for the situations where time matters and improvisation costs evidence.

The sealed packet bag is the outer envelope that turns a collected item into a forwardable exhibit. The packet bag is the thing the FSL receives, logs at intake, and opens under controlled conditions. If the packet fails at intake (torn, unsealed, mis-labelled, missing memo), the exhibit is sometimes refused outright and almost always weakened at trial.

What a correctly prepared sealed packet looks like:

• Outer envelope. Heavy paper or a sturdy plastic-laminated paper. Plastic-only packets are forbidden for biological exhibits because they breed bacteria and degrade DNA.
• Case-identifying label. FIR number, IO's name and signature, case-diary serial number for the item, brief description, date and time of collection, location coordinates (GPS or address), and a tested-for field listing what analysis the IO is requesting.
• Seal impression. Either a wax-thread closure with the unit's brass seal pressed into a wax pool covering the thread, or a numbered security tape that records the seal serial number on the case-diary entry. The wax-thread method is still standard at most state FSLs because it's the version Indian appellate courts have most clearly affirmed.
• Form 95 forwarding memo (the name varies by state) accompanying the packet. The memo lists every packet forwarded under one FIR, with the IO's signature, the seal impression replicated on the memo, and the addressed FSL section.
• Tested-for line. Critical and routinely missed. The FSL section's analysis is bounded by what the IO requested. A blood-stained shirt forwarded for "blood grouping" will not get a DNA profile unless DNA is on the tested-for line.

Most courtroom failures of the sealed packet trace back to the same three causes. Either the seal was broken in transit and not re-sealed under a clear chain entry, the memo was missing the IO's signature, or the tested-for line was wrong and the FSL ran the wrong test. None of these are exotic failures; all of them are the kit's discipline failing at the boundary between the scene and the lab. Chain of Custody covers what happens in court when one of these slips.

A mobile crime scene laboratory (often just "the CSI van") is a vehicle-mounted lab operated by the state FSL. Indian deployments are typically built on a 4x4 SUV chassis or a small truck, with a generator, a powered work surface, a refrigerated specimen compartment, a photography and videography rig, a presumptive testing bench, and a latent-print development station. The van turns a scene visit from a recognise-collect-forward exercise into a recognise-test-confirm-forward exercise, which is faster and more defensible.

The BNSS push made these vans non-optional. Section 176(3) of the Bharatiya Nagarik Suraksha Sanhita 2023 mandates that a forensic team visit the scene, collect physical evidence and videograph the proceedings for every offence punishable with seven years or more imprisonment. The earlier CrPC framework treated the FSL visit as discretionary; BNSS made it the rule. State governments responded by procuring CSI vans at scale.

Where the vans actually run, by mid-2026:

• Delhi. The FSL Rohini operates mobile CSI units across the 15 police districts of Delhi, with a target of one unit per district. Deployed primarily for homicide, sexual offence and major arson scenes.
• Maharashtra. The Directorate of Forensic Science Laboratories runs a fleet of around 59 mobile units across the state, with each district FSL having at least one assigned vehicle. Mumbai's fleet is the largest.
• Karnataka. Roughly 35 mobile units operate out of Bengaluru, Mysore, Mangaluru, Hubballi and the smaller divisional centres. Bengaluru's Madiwala FSL anchors the urban response.
• Gujarat. A state-wide rollout under the Directorate of Forensic Sciences, with around 30 vehicles distributed across districts, the largest concentration in Ahmedabad and Surat.
• Tamil Nadu. Around 40 units across the state, anchored at the FSL Chennai with district reach into Madurai, Coimbatore, Tiruchirappalli and Salem.

Larger fleets are now operational in Uttar Pradesh (75 units, one per district, inaugurated August 2025), Telangana, Andhra Pradesh, Haryana, Punjab and Kerala. NFSU's training centre in Gandhinagar runs the standardised mobile-unit curriculum for state FSL personnel.

What a typical CSI van actually carries (the contents map closely to the investigator's kit, but with scene-side analytical capability added):

• Power and environmental. Onboard generator (3-5 kVA), inverter, multiple 230 V outlets, climate control (specimens degrade in 40°C+ summer interiors).
• Refrigeration. A small forensic-grade refrigerator for biological samples, holding 2-8°C, and a freezer compartment for samples that need lower temperatures pending FSL transit.
• Presumptive testing bench. Folding work surface with reagent racks, calibrated pipettes, disposable plastic pipettes, and the standard reagent set (Kastle-Meyer, leucomalachite, AP, Marquis, Scott, Duquenois-Levine).
• Latent print station. Powder bench, magnetic wand, cyanoacrylate fuming chamber for porous surfaces (some vans, not all), and a dedicated photo bench for development photography.
• Photography and videography. Tripod, full-frame DSLR with macro and wide lenses, video camera with date-time overlay, drone for outdoor overheads (newer vans). The videography kit is the BNSS 176(3) requirement.
• GPS and case-management terminal. A laptop or tablet running the state CCTNS module, with offline capability and sync-on-return.
• Sealed packet bag stock. Multiple sizes, wax-thread rolls, sealing wax, the unit's brass seal, security tape rolls, and a stock of Form 95 forwarding memo books.
• Biohazard handling. Sharps boxes, double-bagged pouches, full PPE for two operators, decontamination wipes for the van's interior between scenes.

Replenishment is the post-scene work that determines whether the kit is fit for the next deployment. Most state SOPs follow a consistent pattern, and the gap between policy and practice is wide enough that it matters in trial.

1. On-scene closure
   Before leaving the scene, the SOCO inventories what was consumed: number of gloves and masks, swabs used, packet bags sealed, reagent vials opened, casting kits expended. The inventory goes into the case diary and the kit's running consumption log.
2. Return to base
   The kit returns to the district or state FSL store-room within the operational window (typically 24 hours). Any sealed packets travel separately with the IO under the chain-of-custody protocol; the kit itself returns with the SOCO.
3. Store-keeper handover
   The kit is signed back in with the FSL's store-keeper, who tallies the consumption log against the returned items. A discrepancy (gloves logged as used but the box still feels heavy, vials missing from the rack) is flagged and investigated. This step is where most state SOPs are weak in practice.
4. Restocking
   Consumables are replaced from the central store: fresh gloves, masks, swabs, packet bags, wax-thread rolls, sealing wax, reagent vials with the new expiry date, casting media, Form 95 memo books. The replacement is logged with batch numbers for traceability.
5. Instrument re-certification
   Re-usable instruments are checked. The camera's flash, focus and date stamp are tested with a calibration frame. The ALS unit's wavelength output is verified against a reference card. The GPS unit's positional accuracy is checked against a known landmark. Any instrument outside its tolerance is pulled out of service and re-calibrated by the FSL's instrumentation cell.
6. Seal stock check
   The unit's brass seal is checked for legibility. Wax-thread stock is replenished. Security tape rolls are checked for serial-number sequence continuity (the next serial in stock is recorded so a torn or missing tape during the next scene is detectable).
7. Operational readiness sign-off
   The store-keeper and the SOCO co-sign the kit's readiness log. The kit is now operational for the next deployment. Most state SOPs require this sign-off within 48 hours of return; longer delays disqualify the kit from urgent response.

The chain-of-custody implication is the bit candidates miss. Every replenishment item that touches a sealed packet (wax, thread, security tape) has to come from a logged stock with a batch number traceable to the state FSL's central store. If the defence at trial argues that the wax used to seal the packet came from an unverifiable stock, the court is asked to doubt the seal. State SOPs answer this by maintaining batch numbers in the replenishment log and recording the batch in use on the case diary for each scene. It's a paper trail, but it's the paper trail that holds the seal at trial.

A few replenishment failures worth recognising:

• The expired reagent. A presumptive vial past its shelf life produces unreliable results. The fix is the six-month rotation discipline.
• The torn packet bag. An unflagged tear in stock means a packet sealed at the scene was already compromised on issue. The fix is the store-keeper's intake check.
• The depleted wax-thread roll. A roll close to the end produces a thin seal that won't hold. The fix is the consumption log triggering a restock at 25% remaining.
• The uncalibrated camera flash. A flash that has drifted in output produces under-exposed close-ups. The fix is the calibration-frame check on every return.