What Are the Responsibilities of Forensic Scientists?

When a crime like a murder, arson, or hit-and-run occurs, it's not just the police and emergency responders involved in the investigation. Forensic scientists also play a crucial role. But what exactly do forensic scientists do? They analyze samples collected from the crime scene by investigators, utilizing advanced technology and their expertise to assist law enforcement in identifying perpetrators, even the most elusive ones.

Introduction to Forensic Science

Forensic science is a field that applies scientific techniques to the justice system, often helping to clarify the details of criminal events. Forensic scientists examine and interpret evidence collected from crime scenes, which can include blood, saliva, fibers, tire tracks, drugs, alcohol, paint fragments, and firearm residue.

By utilizing advanced scientific equipment, forensic scientists identify the elements within samples and compare them. For instance, they might identify that a paint chip from a hit-and-run accident matches a 1996 Ford Mustang convertible, a fiber found at a murder site came from an Armani jacket, or a bullet was discharged from a Glock G24 pistol.

How do forensic scientists transform even the smallest traces into solid evidence that can help identify criminals? Find out next.

Evolution of Forensic Science

Forensic science has a long history that spans thousands of years. Fingerprinting was one of its earliest uses, with the ancient Chinese employing fingerprints to mark business documents. In 1892, Sir Francis Galton introduced the first system to classify fingerprints. Sir Edward Henry, commissioner of the Metropolitan Police in London, created his own system in 1896, which categorized fingerprints by their direction, flow, and pattern. The Henry Classification System became the international standard for criminal fingerprinting.

In 1835, Henry Goddard of Scotland Yard became the first to use physical analysis to link a bullet to the murder weapon. The accuracy of bullet analysis increased in the 1920s when American physician Calvin Goddard helped develop the comparison microscope to match bullets to shell casings. By the 1970s, scientists at the Aerospace Corporation in California pioneered a method for detecting gunshot residue using scanning electron microscopes.

In 1836, British chemist James Marsh created a chemical test for detecting arsenic, which was used in a jury trial. Almost a century later, in 1930, scientist Karl Landsteiner was awarded the Nobel Prize for classifying human blood into various types, laying the groundwork for the use of blood in criminal investigations. During the mid-1900s, new scientific tests were developed to analyze bodily fluids like saliva and semen, as well as to refine blood testing methods.

As new forensic methods emerged in the early 20th century, law enforcement realized the need for a specialized team to examine evidence found at crime scenes. Edmond Locard, a professor at the University of Lyons, established the first police crime laboratory in France in 1910. For his groundbreaking work in forensic criminology, Locard earned the nickname "the Sherlock Holmes of France."

In the 1920s, August Vollmer, the chief of the Los Angeles Police, founded the first American police crime laboratory. When the Federal Bureau of Investigation (FBI) was initially formed in 1908, it lacked its own forensic crime laboratory — it wasn't until 1932 that the FBI established one.

By the end of the 20th century, forensic scientists had access to a wide range of advanced tools for analyzing evidence, from polymerase chain reaction (PCR) for DNA analysis to digital fingerprinting techniques that incorporated computer search functionalities.

Next, we'll explore some of the real-world applications of these modern forensic technologies.

Forensic Drug Testing

Forensic laboratories are frequently called upon to identify unknown powders, liquids, and pills that may be illicit substances. There are two main types of forensic tests used to analyze drugs and other unknown materials: Presumptive tests (such as color tests) provide an initial indication of the type of substance, but they can't give a precise identification. Confirmatory tests (such as gas chromatography/mass spectrometry) are more precise and can accurately identify the substance.

Color tests involve exposing an unknown substance to a specific chemical or chemical mixture. The color change of the substance can offer clues about the type of drug present. Here are a few examples of color tests:

Other methods of drug testing include ultraviolet spectrophotometry, which examines how the substance reacts to ultraviolet (UV) and infrared (IR) light. A spectrophotometer emits UV and IR light and measures how the sample reflects or absorbs these rays, providing insights into the substance's composition.

A more precise method for testing drugs is the microcrystalline test, where a scientist places a drop of the suspected substance on a slide and adds a chemical. The mixture will begin to form crystals. Each drug produces a unique crystal pattern that can be observed under a polarized light microscope.

Gas chromatography/mass spectrometry, however, isolates the drug from any additives or other substances mixed with it. A small sample of the substance is injected into the gas chromatograph. Different molecules travel through the chromatograph's column at varying speeds, depending on their density.

For example, heavier molecules move more slowly, while lighter molecules travel more quickly. The sample is then directed into a mass spectrometer, where an electron beam causes the sample to break apart. The way the substance fragments helps technicians identify what it is.

What techniques do forensic experts use to help identify hit-and-run drivers or arsonists? Find out in the next section.

Forensic Paint Analysis and Arson Investigation

Forensic scientists are often called upon to analyze evidence found in cases of hit-and-runs or potential arson. They have specialized methods for studying small or heavily damaged evidence.

Paint Analysis

At times, forensic scientists need to examine a paint sample, such as when a paint chip is discovered on the body of a hit-and-run victim and investigators are attempting to link it to a specific car make and model.

First, the scientists assess the sample's visual characteristics—its color, thickness, and texture. They inspect it under a polarized light microscope to analyze its layered structure. Then, they can use various tests to analyze the sample:

Arson Investigations

To start a fire, arsonists require a flammable substance and an accelerant, such as kerosene or gasoline. When investigating a crime scene, arson investigators search for these materials. Since only burnt remnants are usually left behind, they collect fire debris and bring it to the forensics lab for further analysis.

The collected samples are sealed in airtight containers before being tested for any traces of accelerants that may have been used to ignite the fire. The following are the common tests performed by forensic labs during an arson investigation:

How do forensic experts examine biological evidence such as blood, semen, or fingerprint oils? We'll explore that in the next section.

Murder Investigations

A murder scene can yield a vast array of evidence, from shell casings to blood and hair. Investigators collect all this evidence, and forensic experts analyze it using different methods depending on the type. For instance, when a gun is discharged, residue is left behind in the gun. Gunshot residue may land on the shooter's hands or the victim. Police use tape or swabs to collect residue from the hands of a suspected shooter.

The forensic technician then examines the sample using a scanning electron microscope. Since gunpowder contains elements that produce a unique X-ray signature, electron microscopy can confirm whether the substance is gunshot residue. The technician may also use chemicals like dithiooxamide (DTO), sodium rhodizonate, or the Greiss test to identify the presence of chemicals formed during gunfire.

Infrared spectrometry/spectroscopy analyzes substances by passing infrared radiation through them and measuring how much of the radiation they absorb. This method identifies the structure and chemical composition of materials like soil, paint, and fibers. Using this technique, forensic experts can compare fibers found on a victim with those from clothing or furniture.

Fingerprinting works by identifying the unique patterns of loops, arches, and whorls on each individual's fingertips. Visible prints are captured on a card or on surfaces that create an impression, such as blood or dirt. Latent prints occur when sweat, oils, and other substances on the skin leave behind prints on surfaces like glass or weapons. These prints aren't visible to the naked eye but can be revealed using dark powder, lasers, or other light sources.

Making Invisible Fingerprints Visible

One method for making latent prints visible in forensic labs involves cyanoacrylate — the key ingredient in superglue. When heated in a fuming chamber, it releases a vapor that reacts with amino acids in the latent fingerprint, producing a white print. Technicians may also use a wand-like tool that heats a mixture of cyanoacrylate and fluorescent pigment, releasing gases that fix and stain the prints on paper. Other chemicals, such as silver nitrate (found in black-and-white film), iodine, ninhydrin, and zinc chloride, also react with oils in fingerprints to reveal latent prints.

Forensic labs employ several tests to analyze bodily fluids like blood, semen, and saliva:

Understanding DNA Analysis

Let's also discuss the crucial role of DNA analysis. DNA is the distinct genetic code that differentiates one person from another. No two individuals share the same DNA (except for identical twins). With modern techniques like polymerase chain reaction (PCR), forensic scientists can identify a person from just a few tiny cells of blood or tissue. PCR amplifies DNA, creating millions of copies from a minute genetic sample.