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Science Detectives

Forensic science is a broad discipline divided into numerous subfields, all of which work together to collect, prepare, analyze and present scientific evidence in criminal investigations.

Forensic scientists use various techniques to accurately recreate and establish the order of events that led to a crime. The physical evidence, meticulously gathered through applying the scientific method, is then used in the court of law to prove someone's innocence or guilt.

In these activities, students practise real-world application of scientific methods in the forensic field, and gain an appreciation of the use of science in both the field and the laboratory to solve crimes.

LIST OF ACTIVITIES

Wink Murder
Black Light Basics
Fingerprint Fun
Finding Fingerprints
Fingerprint Fuming
Chromatography Caper
Plaster Casts

Crime Fighters:

Crime Fighters: Introduction & Case Book Template
Crime Fighters Station 1: Tool Mark Analysis
Crime Fighters, Station 2: Fingerprint Identification
Crime Fighters, Station 3: Handwriting Analysis
Crime Fighters, Station 4: Hair Sample Analysis
Crime Fighters, Station 5: Shoeprint Identification

Objectives

  • Carefully observe actions to infer suspects.

  • Predict, compare and explain why some objects fluoresce under ultraviolet (black) light.

  • Develop and analyze their own and others’ fingerprints through physical methods.

  • Explain how invisible (latent) fingerprints are developed and analyzed through both physical and chemical methods.

  • Create and analyze a cast of impression evidence (e.g. a hand- or footprint).

  • Carefully compare, analyze and record various types of evidence (e.g. shoe prints, tool marks, handwriting, fingerprints and hair/fibre) to infer a likely suspect.

Materials

  • see individual activities for materials.

Background

Forensic science has been popularized through television and pop culture in general. This has promoted forensics to the general public, but it has also perpetuated the “CSI effect”— misconceptions and exaggerated expectations of the applications of forensic science. TV shows often portray a crime scene investigation (CSI) with one or two detectives solving a mystery within an hour. In reality, forensic science involves painstaking collaborative efforts by teams at all levels of law enforcement.

Evolution and development of forensic science dates as far back as 250 C.E. when Greek physician Erasistratus employed the first lie-detector test by studying the rhythm of someone’s pulse.

In the early 1900s, Dr. Edmond Locard was one of the first to propose the concept that “every contact leaves a trace”. This simple yet crucial concept is the very basis of forensic science and in known as “Locard’s Exchange Principle“. It means that in every crime, a criminal will always leave behind a trace, and the job of forensic scientists and law enforcement officials is to find and reveal that trace.

In the 1970s and 1980s, new techniques enabled scientists and other crime fighters to more effectively compile evidence and reconstruct events in the pursuit of justice. Perhaps the greatest development in forensic science came in 1984, when DNA (deoxyribonucleic acid) profiling was made possible through the work of Sir Alec Jeffreys.

As a result of a process known as DNA fingerprinting, thousands of cold cases have been reopened and eventually solved. Cases that have “gone cold” are called so due to lack of new evidence or technology to process evidence- the name is thought to have come from a hunting term, where hounds following a sent were “HOT on the trail”.

Techniques continue to be developed and refined, and the field of forensics has branched out into various fields of expertise. The overlying goal and intent, however, remains the same—to solve crime through scientific analysis of the evidence.

Such specialties within the field of forensic science include, but are not limited to, the following:

Forensic Anthropology
The use of detailed knowledge of anatomy to aid in the identification of skeletal remains and their cause of death, as well as the recovery of remains using archaeological techniques.

Forensic Chemistry
The application of chemistry to identify the nature and composition of a substance or material.

Digital Forensics
The investigation of computer and other digital evidence. It can be used, for example, to investigate whether image or audio files have been altered or deleted.

DNA Analysis
The identification of DNA from bodily evidence found in criminal cases.

Forensic Dentistry/Forensic Odontology
This subfield includes the examination of bite marks, of unknown bodies through dental records, and estimation of the age of skeletal remains.

Document Examination
The identification of forgeries and/or the establishment of the authenticity of documents in dispute. This can include handwriting analysis, or expertise on materials and machines used for printing.

Forensic Engineering
The usage of physical science to discover how events or accidents occurred.

Forensic Entomology
The legal application of the study of insects. In some cases of suspicious death, the length of time that insects have colonized the remains is useful in helping to determine the time of death.

Fingerprint Identification and Analysis
The study of fingerprint patterns and characteristics in order to identify people.

Firearms and Ballistics
The analysis of firearms and bullets found at crime scenes.

Forensic Pathology
The use of expertise in injury interpretation to establish the medical facts in criminal law cases.

Forensic Psychiatry/Psychology
An important subfield covering a range of forensic factors, such as determination of criminal responsibility (i.e. insanity) and competency to stand trial, expert opinion/testimony on questions of a psychological nature, explaining the effects of psychological conditions and illness, and preparing profiles of various types of offenders (e.g. sexual offenders, arsonists, etc.).

Impression Analysis
This requires lifting an impression left behind at the crime scene, such as a tire tread mark, foot/shoe print, traces of a key in a lock, or marks left behind by a tool. The extracted evidence can be used to identify the manufacturer, make or model of the car or shoe, identify a tool and how it was used, or determine what key has been in a certain lock.

Forensic Toxicology
The study of the adverse effects of chemicals on the human body, such as measuring the level of alcohol, drugs or poisons in the blood or hair.

Vocabulary

black light: A lamp that emits ultraviolet (UV) radiation, which is in the long-wave range and emits little visible light.

chromatography: A laboratory technique for the separation of mixtures, like the ink mixture in a felt pen.

cryptology: The science of secure communication (often coding patterns).

cyanoacrylate (superglue) fuming: A technique to uncover latent fingerprints as a result of heating cyanoacrylate, a type of superglue, to produce a gas that adheres to the sweat lift behind by a fingerprint.

dactyloscopy: Fingerprint identification based on comparing and classifying the unique patterns of individual fingerprints.

fluorescence: The emission of light by a substance that has absorbed light or other electromagnetic radiation. This is a form of luminescence.

forensic science: The application of science to law. There are many subfields of forensic science but all aim to find out facts about a criminal case through the application of scientific analysis.

friction ridges: The raised portions of the skin on fingers and toes, the palm of the hand and the sole of the foot. The pattern of friction ridges on our fingers is what creates fingerprints.

impression evidence: A cast created when an object is pressed into a material with enough force to make an impression of the object. Tire tracks and footprints are examples of this type of evidence.

latent: Present but not visible or otherwise “active”.

Locard’s exchange principle: “With contact between two items, there will be an exchange”. This basic law of forensic science assumes that perpetrators of crimes will always leave behind evidence of themselves at the scene, as well as take something with them that can also be seen and used as evidence.

phosphor: A substance that glows.

pigment: A substance that changes the colour of reflected or otherwise transmitted light, as the result of wavelength-selective absorption. For example, we see blue pigment as blue because it reflects blue light back to our eyes.

trace evidence: Any material left at a crime scene, resulting from contact between two surfaces (e.g. shoes and soil, hair and a couch).

Other Resources

Virtual Museum of Canada | SFU Museum of Archaeology & Ethnology | Investigating Forensics

Vancouver Police Museum

PBS NOVA | Teacher Resources | Create a DNA Fingerprint

British Columbia Institute of Technology | Forensics | Gail S. Anderson, M.P.M., Ph.D. | All You Ever Wanted to Know about Forensic Science in Canada but Didn’t Know who to Ask!

High School eLearning | Video| Forensic Science Timeline

Adventures of Cyberbee | Whodunnit | Crime Scene: The Case of the Barefoot Burglar