Issues in Explosives Residue Analysis A Primer for the Bar Frederic Whitehurst, Ph.D.
[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 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
And then there is the problem associated with homogeneous deposition of explosives components. The explosives residue chemist often depends on the fact that when an explosive initiates, very small but detectable amounts of uninitiated explosives can be found on evidence that has been thrown from the seat of the explosion. Unpublished data has shown that when multicomponent explosives initiate, different objects thrown from the area of the blast can have different explosives components on them. For instance, in one crime scene, trinitrotoluene, TNT, was found on one piece of evidence close to the crater during analyses by one forensic laboratory and two other high explosives, RDX and PETN, were found on another piece of evidence found far from the crater by another forensic laboratory. One might infer from these findings that the original bomb contained all three explosives and that when the bomb exploded some of the unreacted explosive deposited on some pieces of evidence and other explosive components deposited on other evidence. It is entirely reasonable that this has had happened with Israeli and British explosives residue experts have also supported this fact.
This might happen because different explosives have different decomposition mechanisms and profiles. And different objects being thrown from the blast center can hold and “protect” explosives residues in different degrees. And yet this data has not been published for peer review by the scientific community. Indeed the discovery of this combination of explosives at one crime scene led the author to review the literature  for possible types of explosives that might give this signature and resulted in a determination that there are numerous explosives composed of many energetic materials which might or might not, upon initiation, result in homogeneous deposition of explosives residues on surrounding material. This is mere conjecture, however, and not allowed as testimony under Daubert. The analyst at the crime scene needs real data to know what objects to return to the laboratory for analysis and that data has not been presented in controlled experiments at this time.
The sampling problem enters into the picture when the chemist must rely on crime scene investigators who cannot practically retrieve all of the evidence from the crime scene. Imagine the sampling conducted at a bombing matter where a large building is involved such as found in the World Trade Center bombing. With thousands of tons of rubble at the crime scene there is virtually no way that the explosives chemist can sample every piece of that rubble for analysis. Therefore if an expert opinion is rendered categorically describing the main charge of the bomb which caused the destruction it would not be reliable if based solely upon the residue analysis data. Rule 702 states that “If scientific, technical or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue an expert may testify thereto.”  Daubert notes further that the word “knowledge” connotes more than subjective belief or unsupported speculation. Without the data to understand what objects may have true representative residue present on them, an unequivocal description of the initiating explosive is mere unsupported speculation and may have very limited probative value while introducing prejudice into the trier of fact’s understanding of the weight of the data. Therefore very qualified expert opinions based upon the data from chemical analysis concerning the “identity” of the explosive used in devices must be held suspect.
 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.
Yinon & Zitrin, supra note 12, at 19, noting numerous mixtures containing many different types of energetic materials.
 FED. R. EVID. 702.