BOMBING INVESTIGATION: A BASIC PRIMER

By Michael Dellarocco

Explosions may occur for many reasons, accidentally or intentionally. Firefighters are generally somewhat familiar with explosions caused by the ignition of natural gas, propane, flammable liquids or vapors, dusts, and even backdraft. The regulated, controlled use of explosives is standard for construction, demolition, mining, and other industries. Fire training has often been limited to the type of explosions firefighters normally encounter and specifically to fire suppression techniques. Most firefighters and investigators have had less experience with intentionally set explosions and their effects.

In the United States and around the world, terrorist activities have been increasing. The April 19, 1995, Oklahoma City Bombing and the February 26, 1993, World Trade Center Bombing in New York City “clearly showed that the threat of terrorism in the United States is real and potentially lethal,” in the words of the Federal Bureau of Investigation publication, Terrorism in the United States.¹

Attacks with explosive devices may occur anywhere. Fire investigators must be prepared to determine whether an explosion has occurred and whether it was intentional or accidental. Explosions may be the work of individuals, organized groups, or amateur bombers. Books such as The Poor Man’s James Bond² and The Anarchist Cookbook³ and information easily obtained on the Internet can make a bomber out of the teenager next door as well as the disgruntled worker or subversive.

This article will help to serve as a guide to some of the basic techniques used in investigating the aftermath of a bombing. It is not a manual in bomb disposal or a technical guide to explosive materials. Disarming an explosive device is the job of experienced and well-trained experts. If needed, technical data on explosive materials can be found in texts such as Explosion Investigation by H. J. Yallop⁴ and Engineering Analysis of Fires and Explosions by Randall Noon.⁵

TERMINOLOGY

The investigator should be familiar with some basic terminology.

Explosion. According to Randall Noon, “An explosion is a sudden, violent release of energy. It is usually accompanied by a loud noise and an expanding pressure wave of gas, which decreases in pressure with distance from the origin. Explosions resulting from the ignition of flammable materials may also be accompanied by a fireball containing high temperatures, which can also ignite nearby combustibles.” (5,85)
Explosives. They are classified as low-yield or high-yield, depending on the rate of the velocity of the explosion or by the rate of deflagration.⁶ Low-yield explosives are rated at a velocity at or below 330 feet per second (FPS). High-yield explosives range from 3,300 FPS to 29,900 FPS.
Deflagration. It “is a very rapid oxidation producing heat, light, and a pressure wave that can have a very disruptive effect on the surroundings.⁷
Detonation. It is “an extremely rapid, almost instantaneous oxidation reaction with the evolution of considerable heat accompanied by a very violent disruptive effect and intense, high-speed shock wave. (7,229) Detonation vs. deflagration. Detonation occurs on a molecular level and “the speed at which the reaction develops the shock wave and temperature rise is supersonic:”⁸ In deflagration, “the burning rate is subsonic as the chemical reaction progresses.” (8, 228) Low-yield explosives, which generally deflagrate, push or move rather than shatter and destroy, as high-yield explosives do as they detonate. A confined or contained low-yield explosive may have a detonation reaction, however; so the investigator will have to rely on other evidence to discover the type of explosive used (see Figure 1). Table 1 demonstrates some of the effects of explosive materials on construction and some types of equipment.

EXPLOSIVES CLASSIFICATION

Explosives are classified by the Department of Transportation as Class A (highly sensitive), Class B (highly flammable and propellants), Class C (detonating cords, explosive rivets, and other manufactured production items), and blasting agents [including ammonium nitrate (ANFO)]. (8, 244) You may already be familiar with these designations.

The form of the explosive used in a bombing may be commercially produced dynamite, plastic explosive, ANFO, black powder in a homemade pipe bomb, or numerous other possibilities. The desired effects, though, are similar.

PRIMARY EFFECTS OF EXPLOSIONS

All explosions have three primary effects:

Blast pressure effect. Two phases occur: the positive pressure followed by the negative pressure or suction phase.
Fragmentation effect. Fragmented materials are propelled outward.
Incendiary thermal effect. Usually seen as a bright flash or a fireball at the instant of detonation. It is usually the least damaging of the primary detonation effects.⁹ It is extremely important that the investigator be familiar with this and other basic terminology and the effects of explosive materials.

The investigator should also familiarize himself with personnel and agencies that can be called if a bombing occurs. These include the local district attorney; state police specialists; the Bureau of Alcohol, Tobacco and Firearms (ATF); the Federal Bureau of Investigation (FBI); bomb scene search specialists; and K-9 search specialists (some may be trained in explosives and others for locating victims and possible survivors). Gathering this information should be done as part of preplanning and training. If an explosion occurs and if a bombing is suspected, get help!

SAFETY A PRIMARY CONSIDERATION

Safety is the primary objective in firefighting operations. Extinguishing fires that may result from explosives attacks may have to be delayed to ensure the safety of firefighters, would-be rescuers, bystanders, injured victims of the explosion, and others. The scene may still contain undetonated live explosives or another explosive device. Responding firefighters and investigators should anticipate the presence of a secondary explosive device. Structures may be severely damaged and unstable. Victims may be injured or dead far from the blast’s epicenter. Consider that the debris from a bombed aircraft may be spread for many miles from the point of the blast. Mercilliott suggests that the unique problems of the bomb scene be considered in three areas: safety, crime scene protection and security, and confusion. (9,121)

Safety, of course, is primary. Only necessary personnel should enter the bomb scene and the area of investigation. A bomb scene is obviously a crime scene. Securing the scene and protecting evidence are also of primary importance. These functions may be more complicated in a bombing scenario, given the number of fire and rescue personnel and agencies involved. Large numbers of curious onlookers and media representatives add to the confusion. The greater the loss of life and the destruction, the more interest there will be. It is up to the investigator to maintain a systematic, well-organized approach to the scene.

The FBI teaches that the investigator should consider three operational phases of the investigation. These phases are functionally divided and mutually supportive. They may be labeled as follows:

outside investigation,
control and coordination, and
inside investigation.

In the ideal situation, the bomb investigators would be well-organized, equipped, and standing by when notified of an incident. In most cities, there are too few incidents to maintain such a force. (9, 123)

THE OUTSIDE INVESTIGATION

This phase is impacted by emergency and safety-related activities, such as rescue and evacuation of victims, as well as preventing further injuries. Activities include evacuating and securing the area, which is in the interest of safety and crime scene investigation. It is crucial that any potential witnesses, including the injured, be identified at this time. Witnesses who leave the scene may take with them information that will be lost forever. If they cannot be interviewed immediately, at least they can be contacted later if they are identified. Photographs of the scene taken by an amateur or news photographers can provide good documentation of events before, during, and after the blast and may contain witnesses and suspects.

When conducting an interview, ask witnesses for further identification. Ask questions such as the following:

Where were you when the explosion occurred?
How long were you in the area prior to the explosion?
Did you see what happened?
What were you doing prior to the blast?
What color was the flash? The smoke?
Did you smell anything in particular?
What did the explosion sound like?
Was there more than one explosion?
Did you notice anything unusual prior to the blast?
Did you notice any unusual persons in the area prior to the blast?
Did you see anyone enter or leave the area after the blast? (9,125)

The outside investigation begins with a physical check of the area, including the preliminary search for bomb fragments. “The distance from the seat of the explosion to the farthest discovered fragment should be multiplied by 1.5, and this distance should be established as the preliminary perimeter.” (9, 126) Figure 2 illustrates this distance.

A suspect located at or near the scene, even if found within two or three hours of the explosion, may have traces of the explosives on his hand if he handled them. Clothing may also reveal traces of explosive materials. Securing this kind of evidence is the job of trained personnel. Again, immediately seek help from outside agencies when it has been determined that a bombing occurred.

It will be necessary to control and coordinate agencies as they arrive on the scene. In Oklahoma City, the incident command system was used; it was expanded as the need arose and proved to be effective. Oklahoma City Fire Chief Gary Marrs served as incident commander throughout the incident; although some problems did occur, the system of control and coordination was successful.

During this phase of the investigation, investigators, as they arrive, should be assigned to do outside investigative work including finding witnesses, locating bomb fragments, and looking for other evidence. A command post should be set up where briefings and liaisons between the agencies can take place.

THE INSIDE INVESTIGATION

According to Mercilliott in Arson in the First Degree: “The inside investigation refers to the crime scene itself, the area most likely to contain parts of the bomb.” (9,130) It includes the following:

Leading. This entails planning, reconnaissance, and providing for the tools and equipment to be used.
Recording. The scene, like any other crime scene, must be “recorded” with photos, sketches, and notes.
Collecting. Finding and securing evidence requires an organized, systematic approach. Several search methods may be used-depending on the degree of destruction in the area, the number of personnel available, and the physical layout of the search area. These methods include spiral, grid, strip or line, and quadrant or zone search. Some sources recommend starting at the outside of the spiral; others suggest beginning at the area near the point of origin (see Figure 3). (9,126)

Evidence may include parts of the explosive device as well as other pieces of related materials. Materials from the epicenter of the bomb’s blast must be retrieved and evaluated for their chemical composition and clues to the type of explosive used. Bomb parts will include the fusing mechanism, the filler or explosive, and the container, although the form of these materials may be substantially changed. Identifying and preserving suspected items will be time-consuming and tedious.

DeHaan, in Kirk’s Fire Investigation, suggests that the investigative process at the scene be remembered as the “Four R’s”: recognition, recovery, reassembly, and reconstruction. (7,244) The investigator must be aware that bits and pieces of bomb parts may be found in the remains of blast victims. Hospitals and morgues should be contacted, and X-rays should be taken to determine the presence of any such evidence.

By planting bomb materials, the bomber always brings evidence to the scene and leaves it there. “In spite of the awesome destruction of some explosions, there always remains some evidence for the skillful investigator to recover and interpret.” (7,250) Of course, witnesses may be invaluable in determining what occurred just prior to the blast and as the explosion occurred. They may help you to piece together answers to some important questions such as the following: What was the reason for the bombing? Was it to maim or kill? Was it to cover another crime? Was it to cause mayhem? Was it part of a plot or conspiracy? Was there a target or intended victim?

This information will help the investigator determine intent or motive. The bomb investigator must show motive, opportunity, and means. Bits of wire, residues, pieces of the explosive device, fibers, and so on, may provide an indication of the opportunity and means to commit the crime. Was the device time activated, action activated, or command activated? Were bomb parts purchased or stolen? Is there evidence that would indicate where the bomb was constructed? Are there fingerprints? Remember, these pieces of information may help make the case. Miscellaneous evidence includes fingerprints, documents, tire tread impressions, shoe prints, hair and fibers, soil, blood, and tool marks. (6,34)

According to an affidavit released by the FBI and reported in The New York Times,¹⁰ investigators were able to obtain the information that on September 30, 1994, 2,000 pounds of ammonium nitrate fertilizer was purchased from Mid-Kansas Cooperative Association in McPherson, Kansas. The receipt for that purchase was found in Terry Nichol’s house. It had Timothy McVeigh’s [McVeigh subsequently has been convicted of the bombing] fingerprint on it. This is the type of connection that investigators must make with the help of resources and agencies beyond the local level. When material is sent to an equipped, appropriate forensic laboratory, for example, samples may be examined by mass spectrometers; sorted according to energy and mass and at the molecular level by type; and microscopically checked for “telltale molecular debris that ellipse will link the bomb materials to specific suspects.”¹¹

Commercially manufactured dynamite may contain taggants, microscopic particles added during the manufacturing process, which can be used to identify when and where the explosives were made. A trace of distribution records will identify the last legal purchaser, according to the ATF. Unfortunately, taggants are not mandatory in the United States. Other clues to the use of dynamite include bits of wrappers, labels, and chemical analysis of residual material. Dynamite is readily available through legal purchase or theft, but the bomber can manufacture or obtain many other explosive materials. The investigator must be familiar at the least with commonly used explosives. They include blasting caps, detonating cord, boosters, permissibles or permitted explosives, blasting agents, water gels, two-part explosives, sheet explosives, and military explosives. (6,11-17)

TYPES OF OBSERVABLE DAMAGE

As evidence is retrieved, examination may reveal clues about what happened, what type of explosion occurred, and the type of explosive involved. It is possible to divide the types of damage observable into three divisions:

Permanent distortion of objects:-Plastic deformation-e.g., bent pipes, bent metal roof members and dishing of metal plates.

-Fracture-e.g., fragmented containers, splintered woodwork and broken glass.

-Fragment attack-e.g., impact craters in metal surfaces and fragments embedded in persons and objects.

Displacement of objects:-Heavy objects-e.g., machine tools, motor vehicles, cookers, and domestic equipment.

-Light objects-e.g., cardboard boxes, fragments of building board, and window curtains.

Flame and heat effects-e.g., scorch marks on paint work and melted nylon fabrics. (4, 43)

These effects, interpreted by experts, will provide much information to the investigator. Only with an understanding of what happened can the investigator adequately prepare his case; this can be done only through the cooperation of everyone involved in the investigation-from the first arriving firefighters or police officers to the prosecutor, who ultimately brings the suspect to trial.

LEGAL CONSIDERATIONS

The investigator must be familiar with legal aspects of a bombing in terms of obtaining necessary evidence, maintaining the security of the evidence, cooperating with law enforcement agencies in regard to other crimes related to the scene, being aware of the rights of any suspects and victims of the explosion. Other legal issues must be addressed through the cooperation of the agencies involved. If preplanning has taken place, the local district attorney should be able to cooperate almost immediately. Federal and state agencies will cooperate in their particular areas. It may be the role of the local investigator to assist these other agencies in the interest of obtaining a conviction.

A bombing incident may be relatively small, or it may be of considerable magnitude. In either case, the investigator will be faced with a situation that is ordinarily outside the scope of everyday investigations. Preparation is the key to dealing with this type of disaster. When it comes to investigating the bomb scene, failure to plan is planning to fail.

References

“Terrorism in the United States,” Federal Bureau of Investigation Terrorist Research and Analytical Center, National Security Division, U. S. Department of Justice, 1994.
Saxon, K. The Poor Man’s James Bond. (California: Atlan Formularies, 1972).
Powell, W. The Anarchist Cookbook. (New York: Lyle Stuart, Inc. 1971).
Yallop, H. J. Explosion Investigation. (Edinburgh: Clark-Constable Ltd., 1980).
Noon, Randall. Introduction to Forensic Engineering. (Boca Raton, Fla.: CRC Press, 1992), 85-95.
Fire/Arson Investigation Manual, New York State Department of Fire Prevention and Control, undated, 9.
DeHaan, John D. Kirk’s Fire Investigation (Englewood Cliffs, N.J.: Prentice-Hall, 1990), 229.
Carroll, John R. Physical and Technical Aspects of Fire and Arson Investigation. (Springfield: Charles C. Thomas, 1979), 228.
Mercilliott, Frederick. Arson in the First Degree. (West Haven, Ct.: University of New Haven Press, 1995), 8-14.
Belluck, Pam, “Suspect Hoarded Bomb Materials, Affidavit Implies,” The New York Times, May 12, 1995, 1.
Browne, Malcolm. “Terror in Oklahoma: The Science Experts Search for Debris to Link Bomb to a Suspect,” The New York Times, Apr 21, 1995, 25.

Additional Resources

Crime Scene and Evidence Collection Handbook. U.S. Department of the Treasury, 1983.
Explosives Tagging; Bureau of Alcohol, Tobacco and Firearms pamphlet; undated.
Explosives Tracing; Bureau of Alcohol, Tobacco and Firearms, Explosives Division, Department of the Treasury; undated.
National Fire Protection Association (NFPA) 921, The Guide to Fire and Explosion Investigation.
Parish, Charles W. “Explosions and Explosion Investigators,” Selected Articles. International Association of Arson Investigators, 1992.
Schultz, Michael J. “The Fire and Explosion Scene Search,” The National Fire Investigator, Spring 1990: 6-7.
Spiegelman, Arthur. “Autopsy of an Explosion,” Selected Articles. International Association of Arson Investigators, 1992.

MICHAEL DELLAROCCO is a deputy fire chief in Schenectady, New York; an arson investigator; and a fire instructor.

Source: Clancey, N.J. ‘Explosive Damage.” Paper presented at sixth International Meeting of Forensic Sciences, Edinburgh, 1972, 4, In Kirk’s Fire Investigation, John De- Haan. (Englewood Cliffs, N.J.: Prentice-Hall, 1990), 247. Reprinted with permission.

Source: Kirk’s Fire Investigation, John DeHaan (Englewood Cliffs, N.J.: Prentice-Hall, 1990), 247. Reprinted with permission.

Source: Arson in the First Degree, Frederick Mercilliott (West Haven, CT: University of New Haven Press, 1995), 132. Reprinted with permission.

Example of a homemade explosive device. (Photo by Patrick B. Dugan.)

Source: Arson in the First Degree, Frederick Mercilliott (University of New Haven Press, 1995), 126. Reprinted with permission.