The Science of Murder

1. Agatha Christie: The Accidental Forensic Pioneer

As a pathology technician who worked in a mortuary, the question I’m asked most often is, “How on earth did you end up working with dead bodies?”

Early fascination. The author's lifelong interest in forensic science began at age eight, sparked by reading Agatha Christie's detective novels. Christie, a former nurse and pharmacist, wove emerging scientific methods into her intricate plots, covering topics like fingerprints, trace evidence, ballistics, and toxicology, particularly poisons, drawing from her wartime dispensary experience. Her stories, featuring dead bodies as central puzzles, perfectly blended the author's biological curiosity with her love for mysteries.

Real-world inspiration. Christie's plots were often stimulated by real-life crimes reported in newspapers, such as the Jack the Ripper case, the Great Train Robbery, and the Dr. Crippen trial. She also drew inspiration from her involvement with the Detection Club, a society of crime writers who discussed real murder cases and forensic techniques, and her second marriage to archaeologist Max Mallowan, which exposed her to archaeological methods that mirrored detective work. This blend of observation, research, and personal experience fueled her remarkable accuracy and ingenuity.

A stickler for accuracy. Despite admitting limited knowledge in some areas, Christie took immense trouble to get her facts right, consulting professionals on police practice, law, and court procedures. She was aware her books educated the public on crime investigation, incorporating details like the importance of leaving a body where found and even anticipating the need for a crime scene kit before it became standard police issue. Her dedication to procedural accuracy made her work believable and contributed to the public's understanding of forensic science.

2. Every Contact Leaves a Trace: The Foundation of Forensic Science

The perpetrator of a crime will inevitably bring something—some sprinkle or spray, some smudge or smear—into the crime scene.

Locard's principle. The fundamental tenet of forensic science, formulated by French criminalist Dr. Edmond Locard, states that "Every contact leaves a trace." This means anyone involved in a crime will leave something behind at the scene and take something away with them, often unknowingly. These tiny transfers, whether hair, fibers, soil, or other materials, serve as crucial forensic evidence linking individuals to places and events.

Beyond the forum. The term "forensic" derives from the Latin "forensis," meaning "of or before the forum," relating to courts of law. While historically tied to legal proceedings, the term has broadened to mean "relating to the application of scientific methods and techniques to the investigation of crime" or even just "in-depth analysis." Medicolegal, an older term, specifically combined medical and legal aspects, highlighting the medical sciences' role in legal investigations.

Christie's understanding. Agatha Christie, an avid reader of Sherlock Holmes and a contemporary of Locard, understood this principle implicitly, even if she didn't always use the term "forensic" or "Locard's exchange principle." Her stories consistently feature evidence linking killers to victims and crime scenes, demonstrating her grasp of how even minuscule clues can be vital. She began using the word "trace" in her stories after Locard's work became more widely known, reflecting her evolving awareness of forensic concepts.

3. Fingerprints: The Enduring Mark of Identity

A fingerprint at a crime scene, usually called a fingermark by today’s CSEs, surely places a person there...

Unique and permanent. Fingerprints, formed by distinctive patterns of ridges and furrows on fingertips, are unique to each individual, even identical twins, and remain unchanged throughout life unless severely damaged. This permanence makes them invaluable for identification, even years after death, sometimes requiring techniques like "gloving" to print decomposed fingers. Their iconic status makes them synonymous with crime and detection.

Patterns and analysis. Fingerprint patterns are categorized into loops, whorls, and arches, with various combinations creating endless variations. Forensic examiners analyze these patterns and minute details like ridge endings and bifurcations to compare unknown prints (fingermarks) found at a scene with known prints from suspects. While early standards required twelve matching details, modern analysis uses a nonnumeric standard combining experience, statistics, and technology for highly accurate identifications.

Christie's use. Christie frequently utilized fingerprints in her novels, demonstrating her awareness of their forensic value from her very first book, published shortly after Scotland Yard established its fingerprint bureau. She depicted various methods of retrieval, including dusting with powder for latent prints and recognizing patent prints made visible by substances like blood or sticky sweets. She also cleverly explored the significance of the absence of fingerprints, suggesting an item had been deliberately wiped, or even the planting of misleading prints, showcasing her sophisticated understanding of this forensic tool.

4. Trace Evidence: Unseen Clues Linking Suspects and Scenes

Wherever he steps, whatever he touches, whatever he leaves, even unconsciously, will serve as a silent witness against him.

Small but significant. Trace evidence refers to minute physical materials transferred during contact, such as hair, fibers, glass fragments, soil, or paint chips, often too small to be easily seen. These tiny clues, embodying Locard's exchange principle, link suspects to crime scenes, victims, or other objects. While early detectives like Sherlock Holmes were known for noticing such minutiae, modern forensic science employs microscopes and specialized techniques for detailed analysis.

Variety of materials. Trace evidence encompasses a wide range of materials, each offering unique information:

• Hair: Human hair can be distinguished from animal hair by its structure (medulla, cortex, cuticle), and microscopic features can link it to an individual.
• Soil: Its complex composition of mineral, animal, and plant matter can indicate a specific location.
• Glass: Fragments can be analyzed for composition and fracture patterns to determine how glass was broken or link pieces from different locations.
• Fibers: Shed from clothing or furnishings, fibers can be identified by type, color, and chemical properties, linking individuals to scenes or victims.

Christie's approach. While Poirot sometimes expressed disdain for "tangible evidence" like cigarette ash and footprints, preferring psychological deduction, Christie frequently incorporated trace evidence into her plots. She depicted characters noticing and interpreting clues like hair on clothing, soil on shoes, or fibers on a weapon, often using these details to corroborate or refute alibis and reconstruct events. Her understanding of trace evidence evolved, moving from simple visual comparisons to allusions of more scientific analysis, reflecting the advancements in the field during her writing career.

5. Forensic Ballistics: Unlocking the Secrets of Firearms

There were ways of deciding what weapon a bullet had been fired from; the marks on the bullet must agree with the rifling on the barrel.

Firearms and ammunition. Forensic ballistics examines evidence related to firearms, including bullets, cartridge casings, and gunshot residue. Different types of guns (handguns, rifles, shotguns) fire distinct ammunition (bullets, shot, slugs) and leave unique marks. Rifling, the spiral grooves inside a barrel, imparts spin to a bullet for accuracy and leaves characteristic striations that can link a bullet to a specific gun.

Analysis and comparison. Ballistics experts analyze the marks left on bullets and casings by the firing pin, breech, extractor, and rifling. These individual characteristics, combined with class characteristics like caliber or gauge, allow experts to determine the type of weapon used and, crucially, match a bullet or casing to a specific firearm. The comparison microscope, improved in the 1920s, revolutionized this process by allowing side-by-side examination of evidence.

Christie's evolving knowledge. Despite admitting limited knowledge of ballistics, Christie frequently featured shootings in her novels, demonstrating a growing understanding of firearms and their forensic analysis. She correctly described concepts like caliber, the difference between revolvers and automatic pistols, and the significance of rifling marks for weapon identification. Her later books incorporated more technical details, such as the ballistics report and the analysis of gunshot wounds, reflecting the advancements in the field and her commitment to research, even correcting earlier terminology mistakes.

6. Questioned Documents: Unmasking Lies in Ink and Paper

Establish genuineness or nongenuineness, expose forgery, or reveal alterations, additions, or deletions

Beyond handwriting. Forensic document analysis examines any material with writing or marks to determine authenticity, identify sources, or reveal alterations. This includes handwriting, typewriting, ink, paper, and even impressions left on underlying surfaces. It's a discipline with ancient roots, used in Roman courts, but it saw significant advancements in the early 20th century with pioneers like Albert S. Osborn, who brought a scientific approach to examining paper, ink, and typewriters.

Handwriting and typewriting. Handwriting analysis compares unknown writing to known exemplars, focusing on individual characteristics like letter formation, spacing, and slant, rather than personality traits (graphology). Typewriter analysis identifies machines based on unique defects in their characters and alignment, especially in older, worn machines. Both methods can link documents to specific individuals or machines, even if attempts were made to disguise the writing or typing.

Christie's use. Christie frequently used questioned documents as pivotal plot devices, from anonymous letters and forged wills to ransom notes and altered checks. She incorporated techniques like handwriting comparison, typewriter identification (noting defects and typing habits), and the detection of alterations or additions. She also explored the use of invisible ink and the recovery of burnt document fragments, demonstrating her awareness of various document examination methods and using them to create intricate puzzles and misdirection for her readers.

7. Impressions and Wounds: Reading the Marks of Violence

It is like seeing a trail of footprints and they are not all made by the same feet.

Marks left behind. Impression evidence is created when one object leaves a mark on another, including footprints, tire tracks, and tool marks. These impressions can be patent (visible), latent (invisible without enhancement), or plastic (three-dimensional). Analysis involves comparing the characteristics of the impression (class characteristics like brand or type) with those of a suspected object (individual characteristics like wear patterns or unique defects) to establish a link.

Weapons and injuries. The marks left on a body, whether bruises, lacerations, incisions, or stab wounds, can also be considered impressions of the weapon used. Forensic pathologists examine these injuries to determine the type of weapon, the force and direction of blows, and the minimum number of impacts. Different weapons leave distinct marks:

• Blunt force can cause contusions (bruises) and lacerations (tears).
• Sharp force (knives, blades) causes incised wounds (longer than deep) or stab wounds (deeper than long).
• Specific tools like screwdrivers or chisels leave characteristic shapes.

Christie's depiction. Christie incorporated impression evidence like footprints and tool marks into her stories, often using them to place suspects at a scene or suggest how a crime was committed. She also demonstrated a detailed understanding of wounds, accurately describing the appearance of injuries caused by blunt objects, knives, and even specialized tools like corn knives. While she sometimes used artistic license regarding the ease of determining a perpetrator's handedness from wounds, her descriptions of injuries and their potential causes were often medically informed and served as crucial clues.

8. Bloodstain Patterns: Decoding the Story Told by Blood

Blood—so much blood—blood everywhere… Blood on the chairs, on the tables, on the carpet…

Silent witnesses. Bloodstain pattern analysis (BPA) interprets the distribution and appearance of bloodstains to reconstruct events at a crime scene. Blood behaves according to physics, creating different patterns based on how it was shed. BPA helps determine how stains were formed, where the blood originated, the type of weapon used, the number of blows, and the movements of individuals during and after bloodshed.

Types of stains. Bloodstains are broadly classified into:

• Passive stains: Resulting from gravity (drips, pools, flows).
• Transfer stains: Created when a bloody object contacts a surface (smears, patterns).
• Spatter stains: Projected through the air (gunshot spatter, cast-off from a weapon, arterial spray from a severed artery, expirated from the lungs).

Analysis techniques. BPA analysts examine the size, shape, and distribution of stains. Elongated stains indicate direction of travel, and tracing lines back from multiple spatter stains can determine an area of convergence or origin. While modern techniques use software, historical methods included "stringing" to visualize the point of origin in 3D. The absence of blood (void patterns) can also be significant, indicating something or someone blocked the spatter.

Christie's use. Despite the perception of her work as "bloodless," Christie frequently depicted bloody scenes and demonstrated a sophisticated understanding of blood's behavior. She accurately described passive stains like pools and drips and used the correct term "spatter" for projected blood. Drawing from her nursing experience, she knew the difference between bleeding from veins and arteries and incorporated this knowledge into plots. She also referenced the clotting process for estimating time of death and even included the use of an anticoagulant (sodium citrate) to mislead investigators about the time blood was shed, showcasing her deep knowledge of blood and its properties.

9. Autopsy: The Body's Final Testimony

The main purpose of an autopsy is to find the cause of death.

Postmortem examination. An autopsy, or postmortem examination, is performed to determine the cause of death, especially in suspicious or unexpected cases. Forensic autopsies focus on identifying trauma, collecting evidence from the body, and reconstructing events, while routine coronial autopsies establish the cause of death and record other pathologies. Autopsies are crucial because external appearances can be misleading, and underlying conditions or subtle signs of foul play might be missed.

Postmortem changes. Forensic pathologists distinguish injuries from natural postmortem changes that occur after death:

• Livor mortis (lividity): Blood settling in lower areas due to gravity, causing purplish discoloration.
• Rigor mortis: Stiffening of muscles in a predictable sequence.
• Algor mortis: Cooling of the body.
• Cadaveric spasm: Rare, immediate stiffening at the moment of death.

Estimating time of death. While challenging, pathologists use a combination of postmortem changes, particularly algor and rigor mortis, to estimate the time since death. Although historically, digestion of stomach contents was also used, this method has been discredited due to its unreliability. Christie's characters often provide precise TOD estimations, sometimes for plot convenience, but she also acknowledged the inherent difficulties and variables involved in real-world TOD calculations.

Christie's knowledge. Christie demonstrated a detailed understanding of the autopsy process, inquests, and postmortem changes. She accurately described signs of strangulation, the difference between antemortem (before death) and postmortem (after death) injuries, and the significance of decomposition. She also incorporated forensic odontology (dental identification) and bite mark analysis into her plots, reflecting the importance of these methods in real investigations. Her knowledge, likely gained from research, attending inquests, and her nursing background, allowed her to weave realistic pathological details into her mysteries.

10. Toxicology: The Science of Detecting Poisons

Since I was surrounded by poisons, perhaps it was natural that death by poisoning should be the method I selected.

The dose makes the poison. Toxicology studies the harmful effects of chemicals on living organisms. Poisons can be corrosive (causing localized tissue damage) or systemic (affecting multiple organs). Historically, poisons like arsenic, strychnine, and cyanide were readily available and frequently used, earning them names like "inheritance powder." Christie, drawing from her experience as a dispenser, had extensive knowledge of these substances and their effects.

Detection methods. Detecting poisons requires chemical analysis of biological specimens taken during autopsy, such as blood, urine, vitreous humor, bile, hair, and nails. Early tests, like Scheele's and Marsh's tests for arsenic, were groundbreaking, allowing for the scientific detection of specific substances. The precipitin test, developed in 1901, enabled the differentiation of human blood from animal blood, a crucial step in poisoning investigations.

Christie's expertise. Poisoning was Christie's signature murder method, featuring in over half her novels. Her descriptions of poisons, their symptoms, and their effects were remarkably accurate, earning praise from pharmaceutical journals. She incorporated both common substances like arsenic and cyanide and lesser-known compounds like taxine and eserine. She also depicted the process of toxicological analysis, from collecting specimens to awaiting lab results, and even included details like the use of sodium citrate as an anticoagulant, showcasing her deep and accurate knowledge of forensic toxicology.

Last updated: May 22, 2025