Introduction to Forensic Science and Empirical Logic
The Nature of Forensic Science and Scientific Error
Scientific endeavors require a commitment to accuracy, yet as human-led activities, they are prone to frequent errors. Even the most skilled scientists make mistakes, which are typically attributed to three primary factors:
Utilization of bad data.
Tools that lack sufficient power or sensitivity for the task.
Unconscious biases of which the scientist is unaware.
The presence of junk science or bad science can lead to catastrophic consequences in the legal system. Errors in scientific application can result in guilty individuals being exonerated and, more critically, innocent people being incarcerated or punished for crimes they did not commit.
The fundamental goal of forensic science is to determine the details of a crime with the highest possible level of accuracy.
Definitions and the Scientific Method
Science is fundamentally based on empirical measurements and characteristics. An empirical measurement is defined as an observable and measurable trait of a substance or interaction. Examples of empirical characteristics include:
Density.
Mass.
Size.
Reflectiveness of light.
Chemical reactions with other substances.
Behaviors and reactions with other people.
The goal of identifying these empirical characteristics is to establish truths about the universe. In a forensic context, these truths answer specific questions about a crime scene:
How did the crime happen?
When did the crime happen?
Who was involved?
Where did it happen?
Forensic scientists typically distinguish themselves from colleagues in criminology and psychology by focusing on the mechanics and facts rather than the "why." While criminology and psychology seek to understand the motivation behind a crime, the forensic scientist focuses on the physical reality, such as the presence of a specific weapon and the resulting injuries.
Honesty regarding the limitations of empirical observations is essential. Scientists must be transparent about how much they can trust their data or what those observations are actually capable of proving.
The "Forensic" Element: The Courtroom as a Forum
The word "forensic" originates from the Latin root word forum. This refers back to the Roman Empire and the concept of an open place for debate.
In the context of forensic science, the place of debate is the courtroom. The courtroom consists of a specific debate involving three main parties:
The Defendant: The specific person on trial.
The Prosecuting Attorney: Whose goal is to prove the defendant committed the crime by presenting evidence.
The Defense: Whose goal is to argue against the prosecution's claims.
The intent of this debate is to convince the jury, also known as the trier of fact.
There is an inherent conflict between the goals of lawyers and scientists. A lawyer's goal is to win the debate and secure a specific verdict (prosecution or acquittal). Lawyers desire certainty and may find it frustrating when a scientist expresses uncertainty, such as stating they are only sure of a result.
Scientists encounter challenges when asked to provide absolute certainty, especially in fields like forensic entomology, where the behavior of insects can be variable and unpredictable.
Processing Physical Evidence
Physical evidence consists of tangible items found at a scene, such as footprints, body fluids, hair, fibers, DNA, or bones.
The role of the forensic scientist is to transform these raw materials into useful information for a case. This is a multi-step process:
Start with the physical stuff (material evidence).
Identify empirical observations (e.g., the length of a specific chunk of DNA).
Distinguish between which observations are important and which are irrelevant, a process that requires significant time and training.
Determine the meaning of the observations (e.g., interpreting a Blood Alcohol Concentration or BAC).
An example of empirical measurement in DNA analysis is measuring the physical length of a segment of DNA that possesses an unusual visible characteristic.
The interpretation of evidence often involves established medical research. For instance, if many beer cans are present at a scene, this suggests significant alcohol consumption. If the measured BAC is , it is compared against the known lethal threshold of to suggest the likely cause of death.
Evaluating Scientific Claims: Wrongness, Lying, and Bullshit
When establishing if a claim is good science, one must distinguish between three types of false or questionable information:
The Wrong: A person who is wrong believes they are correct and they are making a sincere claim, but their conclusion is factually incorrect.
Lying: A person who is lying knows they are not right but makes the claim anyway, showing no regard for the truth.
Bullshitting: A bullshitter is indifferent to the truth. They may think they are right, but they do not know for certain and fail to disclose their uncertainty. They often present opinions or logical guesses as established facts.
To evaluate if a claim is scientifically valid, one should consider:
Credentials and Qualifications: Does the person have the expertise to make the claim? (e.g., an economist may not be qualified to speak on nuclear physics).
Peer Review and Consensus: What do other knowledgeable people think about the claim?
Consistency with Previous Knowledge: Does the claim align with logic and existing scientific principles?
Testing the Relationship: Is there a testable link between the statement and the claim? (e.g., testing "Mega Vitamin Q" by taking before-and-after photos of a large group of people).
Specificity: A scientific claim should be specific rather than broad. Vague statements about "improving the weather" are less scientifically valid than specific, measurable predictions.
The Principle of Falsifiability
The concept of falsifiability is a pillar of construction for scientific approaches. For a hypothesis to be considered "good science," it must be breakable by observations.
A falsifiable hypothesis is one that can be disproved with empirical evidence and does not require an infinite number of observations to be proven true.
Example of Falsifiability (Chicken Eggs):
Observation: An egg is white.
Hypothesis: All chicken eggs are white.
Falsification: The discovery of a brown chicken egg breaks the hypothesis. This is a successful application of the scientific method because the hypothesis was testable and disproved.
Example of Falsifiability (Blood Testing):
Hypothesis: Human blood turns green when exposed to the chemical leucomalakite green.
This is falsifiable because if a sample of known human blood turned a different color (or no color) when exposed to the chemical, the hypothesis would be proven false.
The issue of Uniqueness:
Many forensic theories rely on the idea that certain objects (like fingerprints) are unique and have no exact match in the universe.
Uniqueness is not a falsifiable hypothesis. Finding differences between two prints supports the idea of uniqueness, but to truly disprove uniqueness, one would have to compare an object against every other object in existence (an infinite number of observations).
While uniqueness is a generally accepted theory, modern scientific models prefer hypotheses that are strictly testable and falsifiable.
Professional Development and Education Models
There are different paths to becoming a forensic expert, each with different strengths and weaknesses:
The Experience Model (Police-led): Historically, police officers testified based on their extensive experience with crimes. However, seeing a lot of crime does not necessarily provide the scientific understanding of cause and effect, nor the fundamental knowledge of biology, chemistry, or physics.
The Training Model (On-the-job): This involves taking someone with a high school diploma (the standard requirement for most police jurisdictions) and providing specific task-oriented training. This still leaves the individual at a disadvantage when explaining the "why" or "how" behind scientific relationships.
The Civilian Scientific Model (The Ideal): This is the modern preferred model supported by FEPAC (Forensic Science Education Programs Accreditation Commission). It involves:
Formal scientific education in fundamental sciences to understand how the world works.
Specific training in the police/forensic application of those sciences.
Testifying based on this dual foundation of education and application.
Questions & Discussion
Question: Which of the following is an objective, measurable, and consistent reality: how evil a person is, the size of angels, the number of sesame seeds on a bagel, or how certain you are of an answer?
Response: The number of sesame seeds on a bagel. This is an empirical characteristic that is measurable and exists in consistent reality.
Question: If a person has a BAC of (well above the lethal threshold of ), what are you as an expert willing to back in court? Options included stating she almost certainly died of alcohol poisoning, being certain with no doubt, or stating you cannot draw a firm conclusion.
Response: The preferred answer for the legal system is to state she almost certainly died of this cause. This represents a firm but fair assertion. It provides the strong statement lawyers desire while maintaining scientific integrity by leaving a minute room for doubt. Stating "I don't know" or refusing to draw a conclusion when the data is that clear-cut makes an expert witness essentially unhelpful to the court.
Question: If you see a shoe print at a crime scene that matches a suspect's shoe in size and shape, but the wear patterns (damage to the shoe) found in the blood print are not present on the suspect's physical shoe, what is the conclusion?
Response: The mark was not made by that shoe. The patterns are not the same because the fine details do not match.
Question: If the size, shape, and wear patterns all match perfectly, what is a defensible conclusion?
Response: The print probably came from the suspect's shoe. While it is possible the person lent their shoes to someone else or sold them, it is highly likely the shoes were present at the scene. This is a conclusion that out of people would agree upon based on the evidence.