Bombs and explosives
Bombs and explosives are devices designed to release energy in the form of an explosion, and they have been utilized throughout history for various purposes, from warfare to law enforcement. In contemporary society, these devices have become increasingly prevalent in criminal acts and terrorist activities, posing significant challenges for law enforcement agencies. One major concern is the psychological impact they have on the public; the fear generated by the threat of bombings can often lead to mass hysteria, which can be more damaging than the explosions themselves.
Investigations into bomb-related incidents require meticulous approaches to evidence collection and scene management, as explosions can scatter debris over vast areas, complicating the preservation of crucial evidence. Explosives can be classified by their origin—commercial, military, or improvised—and by their detonation speed, with high explosives detonating rapidly and low explosives burning more slowly under normal conditions. The investigation of explosion sites is inherently risky, as there may be unexploded devices present, and multiple bombs could have been set to target responders.
In summary, understanding the nature of explosives and the intricacies of investigating their use is essential for effective law enforcement and public safety measures.
Subject Terms
Bombs and explosives
SIGNIFICANCE: Although explosives have been used since ancient times, in modern law enforcement they are becoming increasingly popular and deadly tools of criminals and terrorists.
Bombs and explosives present law enforcement with numerous difficulties. The primary difficulty is the fear that such weapons—whether detonated or not—can generate in the public. The fact that mass hysteria alone may cause more damage than an actual bomb makes bombs a weapon of choice of terrorists. Another difficulty is that when these devices are detonated, the force of their blasts has a tendency to scatter and break evidence down into small pieces.
Crime scenes in bomb and explosives investigations extend not only to the furthest reaches of wherever debris from the explosions is thrown but even beyond. An extreme example is the explosion of the space shuttle, which disintegrated over Texas while reentering the atmosphere in January, 2003. Debris from the shuttle’s explosion was scattered over hundreds of thousands of square miles, creating an investigation scene of unprecedented proportions. A similar disaster on a somewhat smaller scale that was an actual crime event was the terrorist bombing of Pan Am Flight 103 over Lockerbie, Scotland, in December, 1988. Not only did that jetliner explode at a considerable height, the explosion occurred over water. The resulting investigation called for the specialized services of divers in addition to the usual forensic team. Some types of explosives degrade in water but others suffer little damage. The shuttle and airliner disasters were unusual, but almost all bomb and explosive incidents pose special problems in controlling crime scenes and preserving evidence.
Collecting and Preserving Evidence
At all explosion crime scenes, systematic and controlled approaches to the collection, preservation, and processing of evidence are essential. Crime scene searches should begin at the most distant points at which debris is found and progress inward, toward the origins of the explosions.
Explosive investigations are similar in many ways to how arson is investigated. In both cases, investigators begin by locating the origins of the fires or explosions. In explosive investigations, the origins of the explosions are frequently marked by craters—the “blast seats”—in which large amounts of explosive residue are generally found. All debris, soil, and surfaces in these areas should be given special attention during the collection phase, and as much material as possible should be sent to labs for analysis. These areas may also contain unexploded, or partially burned, particles that may contain fingerprints, fibers, or hairs that can be linked to the perpetrators.
Investigations should focus on locating as much as possible of the ignition devices and their containers, including wires, tapes, electric switches, timing devices, and batteries. These, too, may reveal fingerprints, fibers, hairs, and other particles that can be used to link suspects to the crime scenes.
Evidence collected in both arson and explosives investigations are also packaged and handled in similar manners. After other sorts of wet evidence—such as blood and semen—are allowed to air-dry, they are packaged in breathable containers. By contrast, arson and explosive evidence, which often contains residues that require laboratory analysis, must be packaged in airtight plastic containers. It is important that these containers not allow the escape of vapors, which may be the only indication of what sorts of accelerants or explosives have been used. As with other forms of evidence, these containers should be appropriately marked and chain of custody should be observed.
Types of Explosives
Explosives are typically classified according to their origins, which may be commercial, military, or improvised. A significant proportion of explosive investigations involve improvised explosive devices, that is, made from ordinary materials available to almost everyone, such as chemical fertilizers. Explosives are also classified according to the speed with which their compounds explode—either high or low. High explosives burn at rates of up to 20,000 feet per second and are said to “detonate.” Low explosives burn at rates under 1,200 feet per second and are said to “deflagrate.” Low explosives are stable under normal atmospheric conditions and burn only when ignited in the open. However, they can explode violently if they are ignited when they are confined.
A variety of tests are performed to determine the chemical makeup of residue found at explosion scenes. For example, chemical color tests are used to identify explosive residue. A device called the gas chromatograph provides the most reliable method to determine the chemical makeup of flammable residues in laboratories. Samples of substances found at explosion scenes are injected into the chromatograph, which then creates a chemical profile of the substance that can be compared to known substances.
Investigations of explosion sites themselves can present significant safety concerns. Scenes of explosions sometimes still have unexploded devices or remnants of devices that present a hazard to investigators. Moreover, bombers often set two or more bombs to explode at the same sites, timing the second devices so that they explode at times when help is likely to have arrived on the site of the first explosions. All explosive investigation scenes should therefore be approached as though yet-to-be-exploded devices still remain at the scenes.
Bibliography
Brodie, Thomas G. Bombs and Bombings: A Handbook to Protection, Security, Disposal, and Investigation for Industry, Police and Fire Departments. 3d ed. Springfield, Ill.: C. C. Thomas, 2005. Third edition of an industry handbook on explosives that was first published in 1972.
Goodpaster, John. "Advances in Detecting and Identifying Explosives After an Attack." National Institute of Justice, 26 Feb. 2024, nij.ojp.gov/topics/articles/advances-detecting-and-identifying-explosives-after-attack. Accessed 22 June 2024.
Kelly, Jack. Gunpowder: Alchemy, Bombards, and Pyrotechnics: The History of the Explosive That Changed the World. New York: Basic Books, 2004. Popular study of the development and impact of gunpowder in world history. Emphasis is on firearm weaponry, but much of the material is relevant to other types of explosives.
Mello, Michael. The United States of America Versus Theodore John Kaczynski: Ethics, Power, and the Invention of the Unabomber. New York: Context Books, 1999. Description of the Kaczynski case by an attorney who assisted in Kaczynski’s appeal.