For those who question why I have the concern for the level of certainty remaining in 921 it is important to look at it from the legal concept. I understand why some have proposed the removal of this section from 921. It is a task group from the committee that is recommending the deletion of the Level of Certainty from the document, Their substantiation for proposed revision is that: Revisions in this edition of NFPA 921 to the recommendations for expressing expert opinions are the result of developments in the larger forensic science community that are intended to make expert opinions better serve the interests of justice. To this end the goal is to make expert reports and testimony more accurate and transparent. The second paragraph of 4.5 stating that the final hypothesis must be uniquely consistent with the facts and the principles of science reflects the wording in 4.3.6 "Test the Hypothesis." It does not require perfection.

Looking at the substantiation the last words seem to be the most important. Throughout the discussion above there has been agreement that the final conclusion based on the use of the scientific method does not and itself indicate that this finding is absolutely correct. Another comment made that I agree with is there are no absolutes in science. It is here where I believe the courts will require some type of level of certainty has to the inclusion being correct. What is presently in 921 gives a user a foundation to make an opinion as to a level of certainty. In most cases an attorney wants you to give them a percentage as to this level of certainty. What 921 did was to give an acceptable level of certainty that is accepted by the fire investigation community to where a specific percentage does not have to be given. By using the terms probable impossible and then defining these terms the investigator can comply with any requirements for a level of certainty based upon what is cited and accepted within the fire investigation community.

The courts have recognized a reasonable degree of certainty since 1935. Where this phrase was not adopted as a standard of immiscibility immediately in 1969 it was adopted by the courts. Where they have accepted this as a standard you cannot find a definition for the degree of certainty in either the federal rules or the state rules. There’s nothing to state in these rules as to what is an acceptable reasonable degree of certainty. Although the definition of reasonable degree of certainty is implied under both Daubert and Frye standards of a miss ability, there is no guidance as to how the terminology should be used when stating an opinion. Because this term is not defined by the courts does not mean that they will not consider this when rendering an opinion as to a person being able to testify. If you can show that this is an acceptable level to be used in your profession, then the likelihood of the courts accepting it is greatly enhanced. If it is removed from 921 then there is no acceptable level for the fire investigation community and will leave it for the court to set their own degree requirements. What would be better is to have one that is already recognized and accepted to were it limits the ability of the other side to attack you on this issue hard to leave it up to a person who has nothing to do with the profession and may not fully understand the reasoning behind not giving a specific percentage figure as to your level of certainty. This is my reasoning for keeping it in the document.

As we previously discussed, the scientific method is a set of steps that if followed will enhance the quality of the conclusion reached by the investigator. When one used the level of certainty of probable over to mere possibilities, based on all opposing hypotheses being proven false, the testimony now becomes highly probative. Here the investigator is using two acceptable methodologies to support his findings. These are the scientific method and the level of certainty. Using both strengthens the person opinion and the chance of it being accepted.

Jim Mazerat
Forensic Investigations Group