Issues in Explosive Residue Analysis: Contamination and cross-contamination 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

Another problem which immediately faces the expert concerns the collection of samples in such a manner that the expert knows that explosives residues seen did not come from the technician collecting the evidence. This is the cross-contamination problem. Explosives residues can be and very often are of submicroscopic size. Unless personnel specifically trained in the proper collection of trace chemical evidence are present at crime scenes there is a likelihood that contamination will take place with evidence. This contamination goes to the issue of chain of custody. “The analytical chemist must be very concerned about the origin of his samples….” [42] Inwinkelried [43] teaches us of weight attacks on the chain of custody. He raises questions concerning the witness omitting precautions that might have prevented substitution, the facts affirmatively suggesting a possibility of substitution, and substitution making the test results worthless. When we normally think of chain of custody, admissibility issues such as the ready identifiability theory and links in the chain of custody come to mind. [44] The reader must remember that explosives residues are very often not visible. A ready identifiability theory would not hold up under examination of the chain of custody of explosives residues. The evidence in question is not the substrate on which the residue is found but the residue itself. Though the witness may be able to identify the object on which the residues were found, she can not, while on the witness stand, look at a piece of residue evidence and identify it by sight if it is not visible. Indeed, explosives residues are just that type of material that does not carry with it identifiable characteristics which differentiate it from any other explosives residues from the same type of explosive.

In State v. Williams [45], for instance, the evidence in question was a gun. The court held that “absolute proof of the chain of custody, possession and control is not required for the introduction of evidence, and that a clear preponderance in favor of its introduction is all that is required.” [46] That proof was established through testimony. Courts have relaxed the chain of custody requirements even to the point where in Williams v. United States [47] the court noted that “The custody of the heroin exhibit, while inexcusably lax and subject to court criticism on that ground, did not here result in such absence of control as to render the exhibit inadmissible as a matter of law…. Nor did the discrepancy in the description of the substance by two witnesses (‘white’ in one instance; ‘tan’ or ‘light tan’ in another) render it inadmissible.”

However we have a very different situation presented to us in Davis. [48] In this matter the chain of custody was established for a gun used in a homicide. A question arose concerning one link in the chain being an individual who was in the military who had had custody of the gun. If this matter involved a criminal bombing and the evidence in question was explosives residues on that gun, the explosives residue analyst could not make any definitive statement about the significance of the presence of explosives on the gun unless that analyst had analyzed control samples from the hands and environment of the individual in the military. The residue which one might have found on the gun could have been placed there by the link in the chain of custody of the gun, the military soldier, and may very well not have originated from the suspect in any way. Though the Ninth Circuit was willing to admit evidence in Williams v. United States even though two witnesses found it to appear to be different in color, tan versus white, it is highly unlikely that explosives residue evidence would be admitted without some very positive proof that it was relevant to the matter at hand and not simply contamination.

In the United States, law enforcement bomb technicians are very often the first personnel to arrive at a bombing crime scene before evidence collection crews come on site. Secondary bombs placed at past bombing crime scenes have detonated resulting in investigative personnel being killed at the scene of the original bombing. Therefore bomb technicians are required at any bombing scene to clear the scene of possible booby traps. Bomb technicians work regularly with raw explosives as part of their job. Invisible residues from explosives adhere to the bomb technicians’ clothing, their equipment, their hands, the boots they wear to bomb ranges, their vehicles and many other objects the bomb technicians touch. [49] Some of the residues degrade over time [50], [51], [52] but other explosives residues stick to surfaces for long periods of time. [53], [54], [55] Normal washing of clothing and hands can remove some residues but not others. [56] Few personnel wash surfaces on the inside of their official vehicles and if those vehicles are utilized by personnel handling explosives then one can expect that surfaces on those vehicles may have significant explosives contamination on them. If evidence samples are picked up and transported by such personnel without due care to avoid contamination, then the explosives expert will generally not be able to offer more than conjecture to the trier of fact as to where such explosives originated from without control swabs from the surfaces which the evidence came into contact with. One can easily imagine the shaking of hands by personnel who arrive at bombing crime scenes. Just that contact can spread contamination to non-bomb technician personnel.

The court is ultimately looking for an opinion from the expert witness which can be rendered within a reasonable degree of scientific certainty. If the expert has no idea whether the explosives residues she is detecting came from the evidence collector or the crime scene then she cannot render an opinion to within a reasonable degree of scientific certainty that the residues originated from the energetic material in the bomb.

The chain of custody is never established and the requirements of relevance and reliability are not met. A solution to this contamination issue, of course, is to have only personnel specifically trained in explosives residue collection and analysis handle evidence that will be tested for residues. This is not always possible and can be cost-prohibitive. However, the court does not recognize this as an excuse. Indeed in Stanczyk v. Black & Decker, Inc. [57] the court specifically addresses this issue: “Plaintiff argues that the net effect of this scrutiny of his expert evidence is to put the claim beyond his financial ability to pursue… This is true, but it is the very nature of Rule 702 and Daubert that requires these expenditures. Proof of any kind is often expensive to gather. Scientific reliability and validity in our times is seldom cheap,…”

In processing massive crime scenes with many sites for evidence collection, the collector of evidence must also be sure that explosives residues from one site are not carried to another site and therefore the chain of custody again broken. For instance, a bombing conspiracy investigation may involve lawful searches of a number of different residences. At one residence the entrance crew, the first law enforcement officers who secure the scene, or the collector of evidence may come in contact with explosives residues that can not even be seen but which are present in what the chemist would consider large amounts. If those personnel pick up objects or even come into contact with objects which have residue on them and then go on to process another crime scene shortly thereafter without proper precautions being taken, there is a high likelihood that the explosives residue will be transferred to the new crime scene. For example, if nitroglycerine is spilled on a carpet in a homemade bomb making facility in one residence, the crime scene investigation crew can and will likely walk over the spill without recognizing its presence. The nitroglycerine residue can only be detected with sophisticated explosives detection equipment or with solvent extraction and analysis on standard analytical laboratory instruments. The nitroglycerine can saturate the soles of shoes without anyone the wiser. And the same crime scene crew can carry that nitroglycerine to numerous other sites.

Such contamination can lead to erroneous conclusions linking different sites to bomb-making activities where in fact the investigation crew itself has transported the explosives from site to site. Such contamination could support evidence of a conspiracy while in reality being manufactured unknowingly by the crime scene investigators themselves. In order for the court to determine if the scientific testimony or evidence admitted is not only relevant, but reliable, the court must ask whether proper controls over evidence have been maintained in these situations. Those controls are doubly difficult due to the fact that most explosives residues are not visible and can be innocently carried from site to site by crime scene investigators. The controls require clean suits that are worn and discarded at each site, controlled access of evidence response team personnel to sites and a thorough identification of all investigative personnel and others who have entered the crime scene. These controls also require control swabs to be taken from individuals who collect evidence from which explosives residues are going to be extracted for analysis. Control swabs should especially be taken from personnel such as bomb technicians who work regularly with raw explosives and personnel who use firearms which contain nitroglycerine-based gun powder. These swabs are necessary to ensure that contamination is not introduced by evidence crews who work with raw explosives on a regular basis. These controls also require strict discipline and adherence to proper protocols.

The FBI has published guidelines for establishing “evidence response teams.” [58] Those guidelines require securing and protection of crime scenes and suggest the use of crime laboratory examiners at the crime scene. In the area of residue analysis, these guidelines are particularly important.


[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.

[42] Fischer, supra note 26, at 10.

[43] Edward J. Imwinkelried, The Methods of Attacking Scientific Evidence, 264-275.

[44] Id. at 83 to 102. 22

[45] State v. Williams, 273 So.2d 280 (1973).

[46] Id. at 281.

[47] Williams v. United States, 381 F.2d 20 21 (1967).

[48] State v. Davis, 249 So.2d 193 196 (1971).

[49] FBI Laboratory explosives experts have found in the past that bomb technician personnel assisting them at crime scenes are often themselves contaminated with explosives residues and therefore could transfer that residue to the objects they come in contact with. For instance at the Super Bowl in Tampa, Florida in 1991, the author worked with a local explosives ordnance demolition (EOD) crew in a security detail. The author and Dr. Dean Fetterolf of the FBI’s Forensic Science Research and Training Center, found explosives residues on many of the objects that the EOD crew used and came into contact with. Those objects included the bomb disposal truck, police vehicles used by the EOD personnel, the hands and clothing of the EOD personnel, door handles the EOD personnel touched, trunks of vehicles the EOD personnel drove and even the EOD bomb dog.

[50] Biodegradation and environmental impact is discussed inYINON, supra note 14, at 33 to 42.

[51] Yinon, supra note 14, at 33 cites Isbister, J.D., Doyle, R.C., and Kitchens, J.F., Engineering and development support of general decontamination technology for the DARCOM installation restoration program, Task 6, Adapted/mutant biological treatment, Phase 1, Literature review, Rep. No. DRXTH-IS-CR-80132 (AD­A110389), Atlantic Research Corp., Alexandria, Va, 1980.

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

[53] Experimental data acquired by the author from analysis of denim cloth placed near exploding dynamite composed in part of ethylene glycol dinitrate (EGDN) explosive has determined that the EGDN is still present on the cloth after over three years. Dr. Alexander Beveridge noted, while he was lecturing at the FBI’s explosives analysis school at the FBI Academy in Quantico, Va. In 1995, that he was aware that nitroglycerine had not decomposed beyond detection over a ten-year period of time on cloth used in the same types of experiments conducted by the Royal Canadian Mounted Police.

[54] Dr. Frank J. Conrad of The Entry Control Systems Division 9252, Sandia National Laboratories, Albuquerque, New Mexico, in explaining the fact that explosives can be found on so many surfaces touched by bomb makers, describes the explosives as sticky. Indeed Dr. Dean Fetterolf of the FBI’s Forensic Science Research and Training Section at Quantico, Va. has advised the author that he has been able to follow test subjects about the FBI’s Academy at Quantico, Va. just by sampling explosives residues on door handles touched by those individuals.

[55] In a paper presented at the Second International Conference on On-Site Analysis: Field Portable Instrumentation, held in Houston, Texas in January 1994, Dr. Dean Fetterolf and coworkers noted that “To demonstrate the transfer of explosives from hands to surfaces a subject touched C-4(RDX). The subject enacted several normal stages in operating a car, including: opening and closing the hood, the driver side door, the trunk, and handling the steering wheel, gearshift, and keys…. After contact, all touched areas showed easily detectable RDX residue. In a separate experiment, after handling C-4, eight consecutive hand washings with soap and water were required before the IMS could no longer detect the RDX.” (The “IMS” is an ion mobility spectrometer which has been tested and utilized by the FBI in the past to screen for explosives residues.)

[56] Washington Post, supra note 2, at H7 notes, “Minute traces of explosives stuffed into a suitcase usually appear on the luggage’s outer surface, as well as on the trunk handle and steering wheel of a car loaded with explosives, researchers said. ‘It can get in the hair of the person’ who has handled a bomb, said David Fine, Thermedics vice president, ‘and take days of showering to get out.'”

[58] Federal Bureau Of Investigation, U.S. Department Of Justice, Suggested Guidelines For Establishing Evidence Response Teams, 1994.

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