Issues in Explosives Residue Analysis: Transportation and storage of evidence in explosive scene investigation

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]

Once the crime scene investigation has been conducted, evidence possibly bearing explosives residues is sent to a crime laboratory for analysis. The mere sending and storage of the evidence can result in data from analysis which is misleading. The following discussion will highlight some of the problems inherent in this area. Explosives are highly reactive materials which can function as oxidizing materials and react with any number of substrates on which they are deposited or can simply evaporate over time. Data from the Sandia National Laboratory [60] notes, for instance, that TNT residues in one instance decomposed significantly during six days of normal transportation. The TNT residues were deposited on a particular substrate and sent to the FBI Laboratory which immediately returned the material unopened. Upon their return, extracts from the substrate determined that the TNT had degraded and “there was significant sample loss.” Other data from biological experiments [61], [62] note that biodegradation takes place in which microorganisms consume explosives. Indeed these experiments have indicated that environmental waste sites involving explosives residues might be cleaned up utilizing these avenues of biodegradation. Kolla [63] notes that degradation of explosives on substrates can lead to incorrect results in the interpretation. Therefore an explosive from a criminal bomb may include, for instance, TNT and RDX high explosives and by the time the explosive residues are analyzed, the TNT and/or RDX which was originally present on the samples may be gone. The expert witness who then testifies categorically that the bomb was composed of an RDX based explosive such as the military plastic explosive, C-4, would be misleading the trier of fact.

How does Daubert address this issue? Counsel may question the expert about whether the expert knows if biodegradation or evaporation or photolytic decomposition may have decomposed one or a number of possible different explosives compounds that may have been left in the explosives residue. The expert cannot know the answer to that question without some basis for the knowledge. In Bradley [64], the court noted that its task was to “determine the scientific validity of a theory or methodology by considering, primarily, whether the proffered testimony: (1) can be and has been empirically tested, (2) has been published and subjected to peer-review, and finally, (3) has been generally accepted in the relevant technical community.” In Bradley, employees in a building in which a pesticide applicator was used failed to establish that the etiology of the multiple chemical sensitivities was sufficiently known or tested so as to allow the testimony of a clinical expert as to causation.

The expert who has a piece of evidence, for instance metal shrapnel, from a bombing crime scene, who knows little if anything about the exposure of that shrapnel to biodegradation factors, or to photolytic decomposition from exposure to sunlight, can only offer conjecture without proof about the original explosive that was in the bomb or even on the piece of shrapnel. The problem is multiplied when the evidence sits for weeks or months or even years awaiting analysis by the residue expert. During those periods of time degradation, even slow degradation, may very well be taking place.

Bradley [65] also dissuades the party offering testimony from responding that the opinion offered is that of the expert and must be disproven by the opponent. “Plaintiffs, as proponents of the testimony, bear the burden of establishing the testimony’s admissibility by a preponderance of proof.” If inorganic oxidizing agents such as are found in black powder and the flash powders in firecrackers are present in residues from these low explosives, one may reasonably expect that chemical reactions, referred to as oxidation-reduction reactions, continue at the points of contact with the oxidizing agents and any matrix material which these chemicals come in contact with. Because the environments in which explosives initiate are not defined before the initiations one does not usually conduct controlled experiments to determine what reactions will take place between the explosives residue and the matrix materials. Therefore, during the transportation and storage phases of the bombing investigation, reactions may take place which render valueless any attempt to answer the question “What was the explosive charge in the device?” Again the word which continues to arise is “may” and the burden of proof is upon the party offering the testimony. Because of the large number of bombing incidents in the world and the paucity of qualified examiners of residues from such incidents, a necessary backlog of cases builds up which often requires storage of evidence for extended periods of time. Some explosives such as TNT and nitroglycerine have very high vapor pressures. [66] Those vapor pressures can result in evidence stored in the same evidence storage facility becoming cross-contaminated. For example, nitroglycerine-based dynamite stored in a three-story building, in the corner of a room on the first floor, was found to be detectable in large amounts in the air of that entire building within three hours. [67] Evidence storage facilities are by their very nature, secure, locked up areas in which cross-contamination of evidence over long periods of time could be very possible.

One may suggest storing those samples with explosives residues which have high vapor pressures in different areas. But what evidence has what residue is not known until analyses are conducted. And following the storage of evidence in such a manner, every surface that the evidence containers touch may be contaminated. For instance, the vapors from TNT residues or raw explosive may saturate the air of the storage locker in which the evidence was stored. The surfaces or shelves in that locker will then be contaminated with TNT. Evidence placed on those surfaces becomes contaminated with TNT. Testimony concerning TNT found on that evidence very possibly misleads the trier of fact into believing that TNT was actually found in the evidence analyzed. Proper packaging of the evidence might help to avoid this cross-contamination issue. However, data concerning testing of proper packaging is not available in the literature and evidence handlers continue to submit evidence in polyethylene ziplock bags which are well known to be permeable to explosives vapors.

A question ripe for counsel to ask is about the storage facilities used for the evidence presented in court. In order to have “scientific knowledge” that contamination has not taken place the expert will have to present evidence of surface testing from surfaces inside the evidence vault. According to Dr. Frank Conrad [68], “We have already alluded to the ‘stickiness’ of these molecules and their action can be simply stated that if they touch anything they stick to it.” Again returning to the guidelines set out by Daubert we have the quote “The subject of an expert’s testimony must be ‘scientific…knowledge.’ The adjective ‘scientific’ implies a grounding in the methods and procedures of science. Similarly, the word ‘knowledge’ connotes more than subjective belief or unsupported speculation.” For the explosives examiner to infer anything from data about presence of residues of certain explosives and to testify in a court of law, her analytical techniques must therefore be well grounded in “scientific knowledge,” i.e., in the methods and procedures of science. Proper scientific methods and procedures require the establishment and validation of appropriate protocols and strict adherence to controls. The court can determine if such measures are in place by asking to review the protocols, determining if the expert followed those protocols and determining if proper controls are in place.

In the area of explosives analysis, the court must ask how evidence was transported and stored, if sampling of transportation vehicles and storage areas takes place on a regular basis, how long samples are stored before analysis and if materials found in evidence could have come from cross-contamination from volatile explosives.


[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.

[60] P.J. RODACY, D. INGERSOL, SANDIA REPORT DAND90-1326. UC-501 (1992) The Collection, Handling, Transportation and Thermal Desorption of Explosive Vapor Using Quartz Collection Tubes.

[61] Tudor Fernando & Steven Aust, Emerging Technologies In Hazardous Waste Management Ii (1991), Biodegradation of Munition Waste, TNT(2,4,6-Trinitrotoluene), and RDX (Hexahydro-1,3,5-Trinitro-1,3,5­Triazine) by Phanerochaete chrysosporium.

[62] Yinon, supra note 14.

[63] Kolla, supra note 52.

[64] Bradley v. Brown, 852 F.Supp. 690 698 (N.D.Ind. 1994).

[65] Id. at 697.

[66] Vapor pressure refers to the ability of individual molecules of a material to leave a surface of that material, to become vaporized, to evaporate. The higher a vapor pressure a material has, the larger the number of molecules that will be able to evaporate off the surface of that material and the higher the concentration of that material there will be in the air above the material. Certain explosives have very high vapor pressures and therefore if placed in confinement such as an evidence vault, they may be able to contaminate other evidence about them just through the evaporation process.

[67] The building was the Forensic Science Research and Training Center at Quantico, Virginia. The incident happened during a test of explosives sniffing instruments and forced the test to be held else whereas the instruments started to detect nitroglycerine every time they were activated.

[68] Frank J. Conrad, Proceedings Third Symposium On Analysis And Detection Of Explosives, July 10-13, 1989, Mannheim-Neuostheim, Federal Republic of Germany, supra note 15, at 1-4.