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4 Detective Methods That Help Catch Killers

Matthew's interests include writing, gaming, movies, and pretending to be Irish despite only having one Irish Great Grandparent.

In 1833, Eugène François Vidocq founded the first private detective agency in Paris, France.

Little did he know that this would pave the way for an entire genre of fiction, with detectives taking their place alongside gunslingers and gangsters as an iconic Hollywood archetype.

The Rise of the Detective

The detective is a product of the industrial revolution, which resulted in mass migration to the city and the need for investigators who could single out suspects among a burgeoning populace.

Arthur Conan Doyle romanticised the profession with pipe-smoking Sherlock Holmes and his superhuman capacity for logic and deduction. In the USA, Humphrey Bogart gave rise to the heroes of noir, while the likes of Frank Columbo popularised the modern raincoat-wearing sleuth.

Here's a look at some of the tools employed by detectives in their pursuit of the truth.

Detective Tools and Techniques

  1. The Crime Lab
  2. The Tools
  3. The Interrogation
  4. The Investigation

1. The Crime Lab

Sherlock Holmes would have considered it cheating, but the crime lab has brought a whole new dimension to police investigation.

Modern crime labs are made up of multiple units, each dedicated to a specific element of crime scene analysis. For example:

  • The Ballistics Unit analyses projectiles and other firearm components recovered from the crime scene.
  • The Drug Unit analyses drugs, pills, powders and liquids relevant to the investigation.
  • The Biology Unit analyses blood, saliva, bone, plant matter, and even insects (plant matter can help determine the geographic location of a crime, while insects from a decomposing corpse help ascertain the time of death).
  • The Trace Evidence Unit analyses fibres, hair, glass and other small materials barely visible to the human eye.
  • The Toxicology Unit analyses poisons and chemicals.
  • The Digital Unit analyses evidence retrieved from electronic devices such as computers.
  • The Fingerprints Unit is dedicated to the analysis of what has long been an iconic element of the police investigation.

A Brief History of Fingerprints

The use of fingerprint records goes back as far as the ancient Babylonians, who would press their fingertips into clay to record business transactions.

But the first conviction based on fingerprint evidence occurred in the USA in 1910, when Thomas Jennings was found guilty of murder as a result of his fingerprints being discovered on the freshly painted railing he used to hoist himself through a window. Police had to cut the railing off so it could be presented in court.

Fingerprints were presented as evidence in English courts for the first time in 1902, a year after Scotland Yard established its first Fingerprint Bureau. In 1911, US courts accepted fingerprints as a reliable form of identification.

2. The Tools

The Homicide Kit

No detective leaves home without their homicide kit, which contains an array of tools for gathering evidence from the crime scene.

Classic elements of the homicide kit include:

  • Powder for revealing fingerprints.
  • Plaster Casting Kit for creating plaster casts of footprints.
  • Equipment for the collection and preservation of evidence that will later be submitted to the crime lab (see detectives with gloved hands dropping evidence into a plastic bag).
  • Flashlights.
  • Chisels for removing wood or metal.

The modern homicide kit includes more advanced tools made possible by scientific advancements, such as DNA swab collection kits.

The Notebook

The image of detectives scribbling in their notebooks is prevalent in film and television, and the notebook remains a simple yet essential tool for real-life investigators. Even in this age of iPads, many detectives still prefer the feeling of the pen in their hand.

Such notes are actually considered official documents and can be used in court.

3. The Interrogation

Contrary to cinematic depictions of angry police officers browbeating suspects, police interrogation is a subtle art that incorporates psychology and strategy.

The most common approach to interrogations is the "Reid Technique", developed by psychologist John E. Reid in the 1950s.

The Reid Technique involves three components:

  • Factual analysis. The suspect is questioned about details pertaining to the crime scene. This relies on information gathered about both the crime and the suspect.
  • Interviewing. Non-accusatory questions, intended to elicit verbal and nonverbal responses from the suspect, based on the assumption that deceptive interviewees will demonstrate certain behaviours, such as avoidance of eye contact.
  • Interrogation. This should only occur once the investigator is reasonably certain of the suspect's involvement. A common method recommended by the Reid Technique is to sympathise with the suspect and provide justification for their crime, thus luring them into a confession.

Alternative Methods

A common critique of the Reid Technique is that it's based on general assumptions about human behaviour that may not apply to the individual in question.

Hence why alternative approaches have been developed, such as the PEACE (Preparation and Planning, Engage and Explain, Account, Closure, Evaluate) method, commonly employed in England.

This method involves listening to the suspect, avoiding leading questions, helping the suspect provide a clear summary of events, and carefully evaluating the suspect's account.

4. The Investigation

Our natural impulse is to take a situation at face value, but the detective has to train their caveman brain to operate in a logical way. For a detective, what you see is not what you get.

Thinking Like a Detective:

Ivar Fahsing, a detective chief superintendent at the Norwegian Police University College, refers to the ABC principle:

  • Assume nothing.
  • Believe nothing.
  • Question everything.

He recommends the following approach to investigation:

  • Determine what you already know based on the information you have, and use that as a starting point; then determine what you don't know and how you can obtain that information.
  • Identify possible explanations for what happened, then seek to eliminate them one by one. This is called abductive reasoning.
  • Use a mind map to record information and track your thought processes (detective films often show the protagonist scrawling notes and diagrams, and pinning relevant articles and photos to the wall).
  • Ensure there's a devil's advocate who can critique your conclusions and provide alternative explanations.

So for all that science has contributed to the profession; the good old art of problem-solving remains one of the most important tools in the detective's tool kit. Sherlock Holmes would approve.


Fahsing, Ivar. How to think like a detective. Psyche.

General information. Britannica.

Orlando, James. 2014. Interrogation Techniques. Connecticut General Assembly.

Uenuma, Francine. 2018, December 5. The First Criminal Trial That Used Fingerprints as Evidence. Smithsonian Magazine.