Issues in Explosive Residue Analysis: The Explosion Crime Scene: Sampling and Homogeneity Issues

Issues in Explosives Residue Analysis A Primer for the Bar Frederic Whitehurst, Ph.D.[1]

[Editor’s Note: This is a multi-part series deigned to educate the defense bar on important issues concerning explosive and explosive residue investigations]

Part 1: Introduction

Part 2: Back to the Basics: Was it the result of an explosive device in the first place? How do we know that?

Part 3: Daubert provides guidance and a means to expose limitations and evaluate explosive investigations, methods, and interpretation

Part 4: The Explosion Crime Scene: Sampling and Homogeneity Issues

Part 5: Disposition Homogeneity in explosive scene investigation

Part 6: Contamination and Cross Contamination in explosive scene investigation

Part 7: Contamination by “Render-Safe” acts of explosives

Part 8: Transportation and storage of evidence in explosive scene investigation

Part 9: Chemical analysis in explosive scene investigation

Part 10: Identifying Techniques in explosive scene investigation

Part 11: Interpretation of data in explosive scene investigation

Part 12: Experience: What makes for a proper expert in explosive scene investigation?

Part 13: Conclusion

Bombing crime scenes can range from a bombing on a vacant street with no response by local inhabitants to the massive destruction, chaos, death, and confusion we are all aware of that resulted when the World Trade Center in New York City was bombed on February 26, 1992. Bombs are designed to create chaos. An explosive used in a criminal bombing is used because it destroys objects, can cause panic and fear, and disorder. Very often when law enforcement and safety personnel arrive at the scene of bombings the destruction is massive, the crime scene has been entered and changed by efforts to save lives, to suppress fires, to establish order from the chaos. The first priorities at these scenes are saving lives, preventing further destruction of property and searching for other possible devices. All of these activities can and do at times alter evidence in such a way that the explosives residue expert can not render valid and helpful opinions about the type of explosive used. The residue analyst who takes part in these investigations must realize the limitations of science in these environments and properly render opinions based upon these realizations.

The analytical chemist must, in drawing conclusions from her data about a larger population, be concerned about the homogeneity of distribution of characteristics and the origin of the sample. The first task of the analytical chemist is to determine that representative samples have been collected that will, when defined, allow the chemist to render opinions concerning the general population from which the samples were collected. Fischer and Peters, for instance, note that, “In practical situations, however, obtaining a sample suitable for analysis is often a source of major difficulty and frequently limits the validity of the final result. The analytical chemist must be very concerned about the origin of his samples and, insofar as is possible, should exercise some control over how samples are obtained…. If it is desired to perform an analysis of a large body of material, it is essential that the sample taken be truly representative.” [26]

When a chemist takes samples from a large powder sample, for instance, he must be sure that the powder is homogeneous throughout if he intends to project opinions about aliquots to the powder in general. There are established protocols which exist to ensure that homogeneity and which all chemists learn of in their initial exposures to the discipline. Likewise, at the crime scene, the collector of evidence must know that representative samples are being collected. Under the Federal Rules of Evidence, the trial judge must ensure that any and all scientific testimony or evidence admitted is not only relevant, but reliable. [27]. If the collector of evidence wishes to determine what explosive was present in the main charge of the explosives device, then he must be sure that he has collected representative samples of residue. Relevance and reliability in this situation start with sampling.

Immediately a major problem looms before us. Because of the chaotic, virtually undefined character of explosions, scientists do not know at this time what pieces of evidence to retrieve from the crime scenes that have representative explosives residues present on them.[28]Besides the chaos of the initiation of the explosive itself, there is the chaos associated with possible reactions of the explosive with materials in the matrix around it [29]and the reactions of those materials among themselves in the extremely high pressures and heats accompanying the explosions.

In freshman chemistry classes, students learn quickly that if a reaction will not proceed by simply mixing chemicals, possibly it can be started with the addition of a little heat. For instance, one college freshman chemistry text [30] notes under the heading “Temperature Effects” in a discussion of chemical kinetics, that “Inasmuch as it is not possible to predict the activation energies of chemical reactions these quantities must be obtained experimentally.” This experimental determination must be conducted while knowing what chemicals are present. Unfortunately at the scene of a bombing, following initiation of the explosive, one can usually only conjecture as to what chemicals were present in the bomb and in the surroundings before the bomb exploded.

In considering this very type of issue, Porter[31] noted that testimony proposed by an expert witness did not pertain to scientific knowledge. The expert testified that, “What I’m giving you now is kind of a curb side opinion. If … you were asking me to give you an analytical, scientific opinion, then, I would have to research it, and I have neither the time nor the inclination to do that.”

We therefore realize that categorical testimony concerning the identity of an explosive based upon residue analysis is not acceptable under Federal Rule 702 without a scientifically sound understanding of three types of chemical reactions taking place at the scene of the explosion. Those reactions include: a.) the decomposition mechanisms of the explosive and the byproducts of the initiating explosive itself, b.) the chemical reaction of the explosive components and byproducts of the explosive with the surrounding matrix components and c.) the decomposition mechanisms and the byproducts of the matrix components reacting among themselves in the severe conditions of high heat and pressure in the area of the explosion.

Defense of expert opinion, which is based on common sense, fails here. “Common Sense” is nonsensical in a chaotic environment. Most often the residue analyst finds herself in situations analogous to that described by the expert in Perreira.[32]The court noted there that “When the special master asked the expert to support his theory…, the expert acknowledged that it was not supported in the literature and that ‘it hasn’t been studied.’ Therefore, we reject the argument that there is support for the expert’s opinion.”

When a bomb explodes in a new and different matrix, surrounded by new materials that have not been investigated before vis-a-vis their interaction with initiating energetic materials, the analyst realizes that she has not studied this particular situation before as in Perreira.

Another problem is that explosives can give off heat producing temperatures ranging over six thousand degrees centigrade. [33]. Those same explosives decompose at below four hundred degrees centigrade. [34] Therefore one would think (and render the “curb side opinion”) that in areas near the blast no residue of the original explosive would survive. Explosives should all decompose, burn up in the high heat of the explosions. And yet residue does occasionally survive in the blast craters. (Obviously the temperature profiles in the vicinity of explosions are not well defined or homogeneous.) The “Why” and “How” of that survival have not been defined using the scientific method as of yet. Modeling each individual situation may be literally but not practically possible.

Just a few years ago, papers in the literature reported methods of establishing what kinds of explosives could be inferred from the residues left after blasts. [35]And yet as Daubert notes in the amicus brief of Nicholas Bloembergen et al. “Indeed scientists do not assert that they know what is immutably ‘true’- they are committed to searching for new, temporary theories to explain, as best they can, phenomena.” [36]This same message is found in Hodges[37 w]here the court states that “In the course of a scientific investigation, a working hypothesis is constantly probed and refined, as data accumulate and alternative theories are either disproved, or adopted as new working hypotheses.” Recent experiments have shown that various components of explosives of known composition are not present in the residues from some explosions of the explosive and yet are present in other explosions of the same type of explosive material used in a different matrix. [38]

Though this data is not yet available in the scientific literature, nor has it been peer reviewed, Daubert allows this type of evidence to be presented to establish testimony as long as it is relevant and reliable. [39]


[1] Executive Director, Forensic Justice Project, Washington, D.C., B.S. Chemistry, 1974, East Carolina University, Ph.D. in Chemistry, 1980, Duke University, J.D., 1996, Georgetown University School of Law. (202)342-6980.

[26] Robert B. Fischer & Dennis G. Peters, A Brief Introduction To Quantitative Chemical Analysis 10 (W.B. Saunders Company, 1969).

[27] FED. R. EVID. 702. 14

[28] The recognition of this lack of knowledge comes from unpublished experimental data derived from research in explosives residue analysis by the FBI Laboratory over the past ten years, and the author’s conversations with respected experts in the field of residue analysis such as Dr. Alexander Beveridge of the Royal Canadian Mounted Police and Charles Midkiff of the U.S. Bureau of Alcohol, Tobacco and Firearms.

[29] P. Kolla & P. Hohenstatt, Stability of Explosives Traces On Different Supports, 60 Forensic Science International 127 (1993).

[30] Bruce H. Mahan, College Chemistry 340 (Addison-Wesley Publishing Company, 1967).

[31] Porter v. Whitehall Laboratories, Inc. 9 F.3d 607 614 (1993).

[32] Perreira v. Secretary of DHHS, 33 F.3d 1375 1377 (Fed.Cir. 1994).

[33] B.T. Fedoroff & O.E. Sheffield, 4 Picattiny Arsenal Encyclopedia Of Explosives And Related Items D-590 (1960).

[34] Rudolph Meyer, Explosives, 3rd Ed. (VCH Publishers, 1987).

[35] A.D. Beveridge, S.F. Payton, R.J. Audette, A.J. Lambertus, R.C.Shaddick, Systematic Analysis of Explosive Residues, 20 Journal Of Forensic Science 431 (1975).

[36] Daubert v. Merrell Dow Pharmaceuticals, Inc. 113 S.Ct. 2786 2795 (1993).

[37] Hodges v. Secretary of DHHS, 9 F.3d 958 966 (1993).

[38] Dr. Dean Fetterolf of the FBI Laboratory’s Forensic Science Research and Training Center and Dr. Alexander Beveridge of the Royal Canadian Mounted Police shared this experimental data as lecturers at a school on explosives residue analysis at Quantico in February 1995. Unpublished data from experiments conducted by the author as well as conversations that the author.

[39] Daubert, supra note 17, at 2795.

Leave a Reply

Your email address will not be published. Required fields are marked *