CLE Forensic Science (Criminalistics): Lab Foundations

CLE Forensic Science — the subject older reviewers know as Criminalistics — is one many reviewers underestimate. It looks technical and sounds intimidating, yet much of it rests on a finite set of facts and techniques. Learn the right facts, drill the right techniques, and it becomes one of the more manageable papers on the board.

PRC's 2026 programme lists seven topic areas under Forensic Science. We'll walk through them.

The Topic Areas of Forensic Science

Forensic Science carries 15% of your weighted average and is the afternoon paper on Day 2 (1:30–4:00 p.m.). PRC's programme lists:

Personal Identification Techniques — fingerprints (dactyloscopy), anthropometry, other identification methods.
Forensic Photography — crime scene photography, lighting, documentation.
Forensic Chemistry and Toxicology — drug identification, blood, semen, poisons.
Questioned Documents Examination — handwriting, forgery, ink and paper, alterations.
Lie Detection Techniques — the polygraph, its components and test formats.
Forensic Ballistics — firearms, ammunition, comparison microscopy.
Forensic Report Writing and Laboratory Safety.

PRC doesn't publish item counts per topic. Bring an ordinary magnifying glass on exam day — PRC's programme lists it as an item to bring.

Personal Identification: The Fingerprint Block

Three frameworks carry most of the fingerprint material:

The three fingerprint pattern types — Loop, Whorl, Arch. Then the subtypes: radial and ulnar loops; plain and tented arches; plain whorl, central pocket loop whorl, double loop whorl and accidental whorl.
The Henry classification system — the primary classification assigns values to whorls by finger position and expresses the result as a fraction. Drill the computation.
Ridge characteristics — ending ridge, bifurcation, dot, island, lake (enclosure), spur, crossover. These are the identification minutiae.

Anthropometry

Bertillon's system. Obsolete in practice, but know its inventor and why it fell out of use — the Will West/William West case, where two men with near-identical measurements were told apart by their fingerprints.

Forensic Ballistics

This is a dense block. Three fields:

Interior ballistics — what happens inside the firearm.
Exterior ballistics — the bullet's flight from muzzle to target.
Terminal ballistics — what happens at the target.

Add forensic ballistics proper — the comparison and identification side: rifling marks on bullets, firing pin and breech face marks on cartridge cases, and the comparison microscope.

Know Your Numbers

Ballistics has numerical items: common calibres (.22, .38, 9mm, .45), calibre designations in inches vs millimetres, and rifling characteristics (number of lands and grooves, direction and rate of twist). Pick one textbook reference and stick to its figures — references can differ slightly, and consistency helps.

Forensic Chemistry and Toxicology

Much of this block sits on a finite knowledge base of named tests:

Drug identification colour tests — Marquis, Mecke, Mandelin, Duquenois-Levine (cannabis), Dille-Koppanyi (barbiturates), cobalt thiocyanate (cocaine).
Blood tests — Kastle-Meyer (preliminary), Takayama and Teichmann (confirmatory crystal tests). Then ABO grouping basics.
Semen tests — Florence and Barberio (preliminary crystal tests), acid phosphatase; microscopic identification of spermatozoa confirms.
Toxicology — Reinsch test (heavy metals), Stas-Otto (extraction of alkaloids).

Questioned Documents and Lie Detection

For questioned documents, drill handwriting characteristics (line quality, slant, alignment, spacing), the difference between simulated and traced forgeries, and ink and paper examination.

For lie detection, know the polygraph's components — pneumograph (breathing), galvanograph (skin conductance), cardiosphygmograph (blood pressure and pulse), and on modern instruments a movement sensor — and the contrast between the Control Question Technique and the Guilty Knowledge Test.

How to Study Forensic Science

Week 1 — Personal identification. Memorise the patterns and ridge characteristics. Drill 50 items.
Week 2 — Ballistics. Build flashcards for calibres, rifling and the three fields. Drill 50 items.
Week 3 — Forensic chemistry and toxicology. Give it plenty of time — there are many named tests. Drill 80 items on drug colour tests and blood/semen tests.
Week 4 — Questioned documents, photography, lie detection, report writing and lab safety. Light reading, heavy MCQ drilling. 60 items mixed.

Finish week 4 with a timed practice set across all seven topics before moving on to the next subject.

Common Traps

Preliminary vs confirmatory — examiners like items where the trap option swaps the two. Kastle-Meyer is preliminary. Teichmann is confirmatory.
Forensic photographer's role — the photographer documents; sketching and evidence collection are separate roles.
Polygraph admissibility — Philippine courts don't accept polygraph results as evidence of guilt or innocence. Items frame this as a scenario.

Forensic Photography: Beyond Equipment

Photography items test concept and procedure, not gear.

Categories of Forensic Photography

Crime scene photography — overall, mid-range, close-up.
Surveillance photography — covert, telephoto, low-light.
Mug shots — front and profile, standardised lighting.
Evidence photography — with scale, identification marker, neutral background.
Aerial photography — for large scenes and major vehicular accidents.

Technical Concepts to Memorise

Aperture — controls depth of field. Smaller aperture (higher f-number) = deeper focus.
Shutter speed — controls motion blur. Slower = more light, more blur.
ISO — sensor sensitivity. Higher ISO = more grain (noise).
Depth of field — the range in acceptable focus. Critical for evidence photography.
Exposure triangle — aperture, shutter speed and ISO interact.

Common Photography Items

Items frame scenarios: a low-light interior crime scene, a moving vehicle, an evidence item that needs to fill the frame. Pick the setting that fits — wider aperture or supplemental light for low light, faster shutter for motion, macro for evidence close-ups.

Questioned Documents: The Examiner's Toolkit

Handwriting Analysis

Know the discriminating elements your reference lists: line quality, direction, slant, alignment to the baseline, spacing, size, proportion, letter formation, connecting strokes, beginning and ending strokes, pen pressure and individual habits. Items frame this as identification — match the questioned document to the standard.

Forgery Types

Simple forgery — the forger writes the name with no attempt to copy the genuine signature.
Simulated (copied) forgery — freehand imitation of a genuine model. Slow, deliberate strokes and hesitation are typical; a well-practised simulation flows better and is harder to detect.
Traced forgery — using carbon, indentation or transmitted light. Traces of guide lines may remain.

Ink and Paper Analysis

Ink comparison, for example by thin-layer chromatography.
Paper analysis — fibre composition, watermarks.
Erasures — chemical (ink eradicators) and mechanical (rubber eraser, blade). Each leaves different traces.

Lie Detection: The Polygraph

The polygraph records several physiological responses at the same time.

Pneumograph — breathing, via chest and abdominal tubes or belts.
Cardiosphygmograph — blood pressure and pulse, via a cuff.
Galvanograph — skin conductance (electrodermal activity), via finger electrodes.
Movement sensor — on modern instruments, detects countermeasures.

Test Formats

Control Question Test (CQT) — compares responses to control and relevant questions.
Guilty Knowledge Test (GKT) / Concealed Information Test (CIT) — tests for knowledge only the perpetrator would have.
Relevant-Irrelevant Test (RIT) — an older format.

Admissibility

The Philippine Supreme Court has held that polygraph tests haven't gained scientific acceptance as a reliable means of telling truth from deception, so results aren't admissible as evidence of guilt or innocence. Items frame this as a scenario where one side offers polygraph results — pick the rejection.

The Forensic Chemistry Memory Bank

Build flashcards for these tests:

Drug Identification — Colour Tests

Marquis reagent — purple/violet for opiates such as morphine and heroin; orange-brown for amphetamines.
Mecke reagent — green to blue-green for opiates.
Mandelin reagent — different colours for different alkaloids and amphetamines; learn the pairings in your reference.
Duquenois-Levine — purple for cannabis.
Dille-Koppanyi — violet for barbiturates.
Cobalt thiocyanate — blue for cocaine.

Blood Tests

Kastle-Meyer — preliminary (phenolphthalein, pink colour).
Luminol — preliminary (blue glow in the dark — chemiluminescence).
Takayama — confirmatory (haemochromogen crystals).
Teichmann — confirmatory (haemin crystals).

Semen Tests

Florence test — preliminary (choline crystals).
Barberio test — preliminary (spermine crystals).
Acid phosphatase — preliminary enzymatic test.
Microscopic examination — finding spermatozoa confirms.

Toxicology Tests

Reinsch test — heavy metals (arsenic, mercury, antimony, bismuth).
Stas-Otto procedure — extraction of alkaloids.

Personal Identification Beyond Fingerprints

Bertillon's anthropometry — historical method, displaced by fingerprints after the West case.
Forensic odontology — bite mark analysis, dental record matching for unidentified bodies.
DNA profiling — STR (short tandem repeat) analysis is the current standard.
Voice identification — spectrographic analysis. Limited acceptance as evidence.

For the broader CLE strategy, see the Complete CLE Guide 2026 and the six-subject rotation. Check the current programme and dates at the PRC — the next CLE is expected around February 2027, not yet announced.

FAQ

Is DNA covered?

Yes, as part of forensic chemistry and personal identification. Know the basics: STR analysis, mitochondrial vs nuclear DNA, and chain of custody for biological samples.

Do I need to memorise specific calibres and bullet weights?

Yes for common calibres — .22, .38, 9mm, .45, .357. Bullet weights matter mainly when comparing similar calibres (9mm vs .380).

Is forensic photography purely technical?

No. Items mix technique (lighting, focus, depth of field) with documentation rules (overall, mid-range and close-up shots, with and without scale).

How much of the polygraph should I know?

Lie detection is one of the seven topic areas. The instrument's components, the main test formats and the admissibility rule are the essentials.

How reliable are the colour-test associations?

The textbook associations are stable, though real lab work shows false positives — which is why colour tests are preliminary. The exam rewards the textbook association. Learn it cleanly first.

Is questioned documents worth deep study?

Yes. Handwriting elements, forgery types and ink/paper examination cover most of it. Drill 50 items and review every miss.