As investigators, we are not truth seekers, but fact finders. We rarely discover “the whole truth and nothing but the truth.” Moreover, although we may discover a lie or two along the way, it’s not up to legal investigators to decide what the “truth” is. It’s up to us to find information, facts, and evidence.
Of course, not all information is factual, nor is it evidence. Information may be a witness statement or a fingerprint, a report or an observation. But it’s not considered “evidence” unless it has the potential to prove or disprove an assertion, allegation, or event.
Facts become evidence only when verified by the investigative process.
For example, we may discover DNA during our investigation. This is information. But is it evidence of guilt or innocence?
Indeed, it is not. Until we can establish how and why someone’s DNA arrived at the scene, its presence is merely unconfirmed and unfiltered information. The task of the legal investigator is to seek additional facts that tell a more complete story of that DNA.
That story may lead an investigation toward more facts, or to an important piece of evidence that proves where someone was (or wasn’t) during a crime. But as investigators, we’re not in the business of finding the “truth.” We’re in the business of collecting and documenting information and evidence, and carefully scrutinizing its provenance. We take into account subjectivity and bias, and flawed perceptions and memories.
But we must resist any temptation to extrapolate subjective interpretations from objective facts. That’s the jury’s job, not ours.
The Exchange Principle
When we discover a piece of information, the first question facing us as investigators is: How did it get there?
Edmond Locard, a pioneering criminologist known as the “Sherlock Holmes of France,” conceived of an organized approach to this question in the early 20th Century. He introduced a core principle to the field of forensic science: “Every contact leaves a trace,” he said—a concept which came to be known as “Locard’s Exchange Principle.”
In his 1953 work, Crime Investigation: Physical Evidence and the Police Laboratory, Paul L. Kirk explained the principle like this:
“Wherever he steps, whatever he touches, whatever he leaves, even unconsciously, will serve as a silent witness against him. Not only his fingerprints or his footprints, but his hair, the fibers from his clothes, the glass he breaks, the tool mark he leaves, the paint he scratches, the blood or semen he deposits or collects. …Physical evidence cannot be wrong, it cannot perjure itself, it cannot be wholly absent. Only human failure to find it, study and understand it, can diminish its value.”
Tracing how this “exchange” happens is an important step in converting raw information into useful evidence. I think of it in terms of an “evidentiary triangle,” with the following three sides:
Person to Scene: Someone leaves a trace of some material at a crime scene, such as fingerprints, hair, or blood.
Scene to Evidence: A piece of evidence contains a trace of some material known to have come from the crime scene, such as a carpet fiber found on a murder weapon.
Evidence to Person: A trace of some material linked to the crime scene is found on a person—for example, blood found at the scene is discovered under someone’s fingernails.
These connections pertain to both circumstantial and direct evidence, as presented by fact and expert witnesses, and heard by the judge and jury. Any break in the connection calls the evidence into question.
If we return to our discovery of DNA earlier in this article and apply the evidentiary triangle, we can work toward learning the DNA’s “backstory”: Whose is it? Where did we find it, at the scene or attached to a piece of evidence (such as a weapon)? And what is the “transfer” relationship of the DNA—person to scene, scene to evidence, or evidence to person?
Until we know more, the presence of another person’s DNA at a scene or on a weapon or victim is not proof of guilt, nor is the absence of DNA proof of innocence.
Making a Murderer
“Making a Murderer,” a riveting 2015 documentary about criminal justice in a small Wisconsin town, had millions of Americans suddenly debating issues of information and evidence, bias and objectivity. Filmmakers followed several murder trials and raised serious questions about how some of the evidence was handled and interpreted, and whether it had been contaminated or even planted.
Some of the evidence presented seemed damning, such as the victim’s burned bones found in a fire pit on the suspects’ property. But certain facts (at least, as presented onscreen) proved more slippery: A trace of one suspect‘s blood found in the victim’s car pointed to his guilt—until defense attorneys discovered a broken seal in the blood sample vial in the police evidence room; the victim’s car key, found in a suspect’s bedroom, told a different story when some witness accounts suggested that police may have placed the key there themselves.
Based on the evidence viewers “heard” in the documentary—as filtered through the filmmakers’ own biases and choices—no single story of the crime emerged. But it seems likely that police either catastrophically bungled the job of collecting and handling evidence, or one or more of them actively tampered with it. Either way, viewers were left with the impression that the evidence was seriously compromised, and that it told no clear truths about what happened to a young woman one autumn day in 2005 (and who was responsible for it).
After the documentary came out, there was a public outcry to exonerate the subjects of the documentary. But despite very compelling information that raised questions about the fairness of the men’s trials, no factual evidence emerged that pointed to their innocence with any certainty. The prosecution’s story of the evidence won in court—both men were convicted. And the filmmakers’ version won in the court of public opinion.
But in the end, the truth could not be known; only doubt remained.
The questions raised in the documentary are also key questions when reviewing a case for investigation, pre-trial, trial or post-conviction.
Our civil and criminal trial system is based on direct and circumstantial evidence, from reasonable suspicion to probable cause and beyond a reasonable doubt for criminal, and preponderance of the evidence in civil. As fact investigators, and sometimes offering an opinion as an expert, knowing these distinctions is important. Knowing how these interact is more important.
Direct evidence is defined by the Lectric Law Library as “evidence that stands on its own to prove an alleged fact, such as testimony of a witness who says she saw a defendant pointing a gun at a victim during a robbery” and “direct proof of a fact, such as testimony by a witness about what that witness personally saw or heard or did.”
An example of direct evidence would be a witness to an event, such as an armed burglary and shooting.
Circumstantial evidence is defined by the Legal Dictionary as “information and testimony presented by a party in a civil or criminal action that permit conclusions that indirectly establish the existence or nonexistence of a fact or event that the party seeks to prove.”
An example of circumstantial evidence would be finding an ejected shell casing in the vicinity of a shooting event.
How They Interact
Generally, no single piece of evidence can prove or disprove the elements of a crime. It is a series of established facts in evidence that define the crime, place, date and time, or persons involved. These are governed by the rules of evidence.
In the case of a witnessed burglary and shooting, a fact witness may identify a suspect, and an expert witness may connect the toolmark on the shell casing to a specific firearm. Additional evidence may connect the firearm to a shooter and the event. Together, those elements may connect the suspect and firearm to the event, although not necessarily conclusively.
Unlike facts portrayed in riveting crime documentaries, evidence admitted at court must be relevant, material, and competent. Here’s how the “concept of admissibility” is defined at FindLaw:
“To be considered relevant, it must have some reasonable tendency to help prove or disprove some fact. It need not make the fact certain, but at least it must tend to increase or decrease the likelihood of some fact. Once admitted as relevant evidence, the finder of fact (judge or jury) will determine the appropriate weight to give a particular piece of evidence. A given piece of evidence is considered material if it is offered to prove a fact that is in dispute in a case. Competent evidence is that evidence that accords with certain traditional notions of reliability. Courts are gradually diminishing the competency rules of evidence by making them issues related to the weight of evidence.” 
To ignore these concepts of evidence is to begin to play into the drama of the event and persons involved. As investigators, no matter who retains us or why, we have no interest in the case or outcome—only the evidence. So long as our focus is on the facts, our purpose is complete and our goals accomplished.
About the author:
Dean A. Beers, CLI, CCDI is a Certified Criminal Defense Investigator (CCDI) and an expert consultant & witness in criminal and civil equivocal death investigations. He is also certified in Medicolegal Death Investigations. With his wife, Karen, he co-developed “Death Investigation for Private Investigators” distance learning and continuing education for PIEducation.com, and also at MedicoLegalDeathInvestigations.com.