The Pitfalls of Modern Investigative Methodology Using Negative Corpus

Conclusions regarding the cause of a fire, explosion, subrogation issue, or even a construction defect are often made in the absence of physical evidence or proof.  The term Negative Corpus is not a legal term, but refers to a loose Latin translation meaning “without the body of the crime.”  Many forensic investigators utilize the process of elimination in their examination.  Simply stated, they use statements such as “I eliminated all other causes, thus it has to be…….” Or, “via the process of elimination, it is my conclusion that the cause is…..”  These statements were acceptable for a long time in the fire investigation industry, but they are now being challenged.  There are organizations that are now pursuing the freedom of alleged arsonists who were convicted without positive proof of arson.
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In the past, a few rare case studies have shown some acceptance of this procedure of ruling out other causes to render an opinion. However, more recent cases such as Magna Tek are requiring proof in addition to ruling out other causes. One can think of the familiar term, “where is the smoking gun?” No longer can an investigator with an impressive resume walk into court and use the formally accepted term, ipse dixit, which means “it is because I say it is.” Courts are now asking for proof, not just elimination of all other causes. In a fire investigation, this means utilizing the Scientific Method.  This requires the investigator to define the problem, gather the data, analyze the data, formulate a hypothesis, and test that hypothesis using accepted methodology.  Using accepted methodology now requires that the theory be backed up with scientific proof of the theory, peer-reviewed articles, or accepted lab testing.

NFPA 921, a commonly referred-to guideline for fire investigations, specifically implies that fire investigators determine fire cause using three elements: the ignition source, the material first ignited, and the ignition sequence.  Negative Corpus fails do this by avoiding the actual proof of cause. In the text Fire Scene Reconstruction, DeHaan/Icove state: “ The use of “negative corpus” or “arson by default” approach (the methodology of ruling out all accidental causes for a fire without scientific fact and the Scientific Method) is rarely an acceptable methodology for determining that a fire was intentionally set.”

A savvy defense attorney, be it in a civil or criminal case, will certainly create enough doubt in the mind of the jurors if an investigator uses Negative Corpus as the only basis of their case. Forensic investigators must not only eliminate all other pertinent and logical causes, but must also focus on the cause, utilizing accepted scientific techniques.  Too often, investigators will stop at the stage where they have to prove the cause using the Scientific Method because they do not know how or they cannot prove the cause scientifically. In the case of Daubert vs. Merrill Dow, the judge ruled that the expert’s opinion is only valid if they can prove cause using accepted scientific methods or if their conclusion is based on proven theories in the relevant field.  Without a specific origin and cause, the use of Negative Corpus is subject to irrevocable error and discredits the entire industry. Fire investigators are often under extreme pressure from prosecutors or insurance companies to determine cause. However, the prudent investigator is not afraid to admit that the fire cause cannot be determined and to list the cause as such.  It is completely acceptable to list the fire as “Undetermined.” This does not imply that the case was poorly investigated; it merely means that each developed hypothesis could not withstand an examination by deductive reasoning.  In the long run, this will only assist in improving credibility in the fire investigation field and save a significant amount of money and time on criminal or civil cases that cannot be proven using modern standards.

Outside the realm of fire investigation, Negative Corpus can lead to improper or flawed conclusions as to the cause of damages or defects at a home during an insurance claim.  The application of the Scientific Method to every investigation performed by a forensic engineer should lead to a conclusion regarding the damage that can be backed up by science.  Simply because an engineer cannot identify a single cause of the damage at the home does not mean that we are being “wishy-washy” or vague; rather, it means that if we were pushed in court, we would not be able to determine a single cause beyond a reasonable degree of scientific/engineering certainty.  Unless the evidence is overwhelming in one direction or another, the conclusion of a single cause cannot be determined.

The application of Negative Corpus may lead an individual to become an advocate for their client and not an advocate for the truth.  Advocacy for the truth allows an individual, fire investigator, or engineer to always search for the truth regardless of what the best outcome for their client will be.


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