Criminal Law Chapter 19 Detection Fire Accelerants Several Types Portable Equipment

Chapter 19: Arson and Explosives Investigation

Swanson: Criminal Investigation, 13e

IM-19 | 1

Chapter 19

Arson and Explosives Investigations

Learning Objectives

1. Discuss the steps in the preliminary investigation of arson.

2. Be familiar with various types of burn indicators.

3. Describe ignition devices that may be used in arson.

4. Assess several common motivations of arsonists for setting fires.

5. Explain the scientific methods used in arson investigation.

Introduction

Arson is an inherently difficult crime to detect and prosecute, in part because the motivations for

and methods of committing arson vary widely. Some arsonists may be troubled juveniles who

start fires with matches or cigarettes, others are professional arsonists who frequently use timing

devices and accelerants. Arson investigation also falls between police and fire department

In the second half of this chapter, explosive investigations, which are in many respects quite

different from arson investigations, are discussed. A detailed discussion of the different types of

explosives used and the techniques employed to detonate them will be provided. Improvised

Chapter 19: Arson and Explosives Investigation

Swanson: Criminal Investigation, 13e

IM-19 | 2

Lecture Notes

I. Preliminary Investigation

One effective way to determine fire causes is to determine the point of origin. After the area of

origin has been established, the investigator should check for the level of origin by examining the

II. Where and How Did the Fire Start?

Once the fire is put out, the primary task is to begin examining what is left of the building for

physical evidence that may indicate how the fire began. The point of origin can be a clue to

possible arson.

A. Two Factors Needed to Cause a Fire

During the investigation, it should be borne in mind that a fire always has two causes: a

B. Accidental Fires

Once the point of origin has been discovered, the next step is to determine how the fire

C. Spontaneous Heating and Ignition

There are a few fundamental causes of spontaneous heating, but the conditions under which

Chapter 19: Arson and Explosives Investigation

Swanson: Criminal Investigation, 13e

IM-19 | 3

III. Burn Indicators

Burn indicators are the effects of heat or partial burning that indicate a fire’s rate of

development, points of origin, temperature, duration, and time of occurrence as well as the

A. Alligatoring

Alligatoring is the charring and cracking that gives wood the appearance of alligator skin.

B. Depth of Char

Analysis of the depth of char is most reliable for evaluating fire spread, rather than for

C. Breaking of Glass

Glass that has received an impact will have a characteristic “cobweb” pattern: numerous

D. Collapsed Furniture Springs

The collapse of furniture springs may provide the investigator with various clues concerning

E. Spalling of Concrete

Spalling is the breakdown in the surface tensile strength of concrete, masonry, or brick that

F. Distorted Light Bulbs

Chapter 19: Arson and Explosives Investigation

Swanson: Criminal Investigation, 13e

IM-19 | 4

Heat can also have an effect on the glass of a light bulb. The investigator can examine the

distortion of a light bulb, for instance, to determine the direction of head impingement.

G. Temperature Determination

If the investigator knows the approximate melting temperature of a material, an estimate can

IV. Firesetting and Related Mechanisms

An incendiary mechanism may be mechanical or chemical, and consists of an ignition device,

A. Ignition Devices

Only juvenile arsonists and pyromaniacs seem to favor striking matches. Other firesetters

B. Telltale Signs of Accelerants

Some of these signs are as follows:

• Distinct burn/damage pattern

• Burns to the hands, face, legs, or hair of a suspect/witness

Chapter 19: Arson and Explosives Investigation

Swanson: Criminal Investigation, 13e

IM-19 | 5

Even the ordinary firesetter sometimes uses a chemical that ignites on contact with water.

Most chemical ignition units leave some residue, have a distinctive odor, or both. Although

C. Plants

A plant is the material placed around the ignition device to feed the flame. Accelerants are

also usually part of the plant.

D. Trailers

Trailers are used to spread the fire. A trailer is ignited by the blaze from the plant. It carries

the fire to other parts of a room or building.

E. Missing Items

V. Arson for Profit

Understanding the motive of the arsonist is extremely important if the investigation is to be

A. Financial Stress as the Primary Cause

The home or business owner who decides to arrange an arson fraud may do so out of

submission to financial stress. The businessperson on the brink of insolvency faces financial

Chapter 19: Arson and Explosives Investigation

Swanson: Criminal Investigation, 13e

IM-19 | 6

be motivated by the desire of the owner to secure enough money to remodel or move. A short-

term cash-flow problem can be caused by an unusually large buildup of slow-moving

Many types of arson occur because of the actual or anticipated problem of financial stress;

others result from schemes where there was not, and probably would not be, any financial

problem. These types of arson-fraud schemes result from the planning and plotting of

professional fraud schemers and their associates. In cases where a defined tract has been

B. Arson Generated by Third Parties

This is another broad category of arson for profit, where the beneficiary of the fire is not the

owner-insured but a third party who arranges for the fire out of some economic motive.

The following are some examples of major forms of third-party arson:

• The elimination of business competition: This type of scheme is motivated by someone

who seeks to create a business monopoly or at least to maintain a competitive edge.

VI. Other Motives for Arson

A. Revenge-Motivated Arson

Revenge-motivated fires are set in retaliation for some injustice, real or imagined, perceived

Chapter 19: Arson and Explosives Investigation

Swanson: Criminal Investigation, 13e

IM-19 | 7

by the offender. The primary motive of revenge can be divided into four subgroups. The

subgroup with a personal revenge motive, as the name implies, uses fire to strike at an

VII. Detection and Recovery of Fire-Accelerant Residues

Because flammable liquids flow to the lowest level, heat travels from this level up, and the

A. Alternative Fuels in Fire Debris Analysis

Biodiesel fuel is one of the most common alternative fuels and is now readily available in

many parts of the United States and around the world.

VIII. Scientific Methods in Arson Investigation

The presence of flammable liquids may establish arson and sometimes link a suspect to the fire.

A. Detection of Fire Accelerants

Several types of portable equipment are available to the arson investigator for detecting

residues of flammable liquids at fire scenes. The sensitivity of the human nose to gasoline

vapor is about one part per 10 million. Chemical color tests may be used to detect both liquid

accelerant residues and their vapors.

Chapter 19: Arson and Explosives Investigation

Swanson: Criminal Investigation, 13e

IM-19 | 8

IX. Interviews

To establish possible motives and develop suspects, the arson investigator must interview people

who might know about the fire and how it started. The following kinds of people may provide

information.

A. Questions to Ask Witnesses

Prospective witnesses include tenants, businesspeople, and customers from the burnt building

or surrounding buildings, as well as passersby such as bus drivers, taxi drivers, delivery

Here are some questions that a witness can be asked:

• Did you observe the fire?

Firefighters can be an invaluable source of information to arson investigators because of their

technical knowledge and what they observe at a fire.

Here are some questions that the firefighter can be asked.

• What time was the alarm received?

Chapter 19: Arson and Explosives Investigation

Swanson: Criminal Investigation, 13e

IM-19 | 9

Here are some questions that the agent or broker can be asked:

• Who is the insured?

Here are some questions that the insurance claims adjuster can be asked:

• Did you take a sworn statement from the insured?

Here are some questions that the insurance investigator can be asked:

• Were you able to determine the cause of the fire?

The insurance industry maintains a modern computerized data bank, the Property Insurance

Loss Register (PILR), to keep track of fire, burglary, and theft claims. PILR is a listing of

everyone who has an insurable interest in fire claims and a listing of only the insureds in

burglary and theft claims. Thus, PILR is one of the most effective routes for determining a

repeated pattern of claim activity on the part of individuals and organized rings.

B. Interviewing a Suspect

The following questions are based on the assumption that the person to be interviewed is

involved in arson for profit, that the investigator has enough evidence to make an arrest or to

convince the subject that he or she is liable to arrest, and that the subject is more valuable to

the investigation in a cooperative role than as a defendant.

Here are some questions that the suspect can be asked:

• What method was used to accomplish the arson?

Chapter 19: Arson and Explosives Investigation

Swanson: Criminal Investigation, 13e

IM-19 | 10

Here are some additional questions to ask a suspect, when a potential “torch” or firesetting is

identified:

• Are you willing to cooperate in this investigation?

C. Interviewing the Target and the Owner

The target of the investigation may be an owner, a landlord, a fire broker, or the like. The

Here are some questions that the target can be asked:

• Tell me in your own words what you know about this fire.

Here are some questions that the owner can be asked:

• Tell me in your own words what you know about this fire.

D. Interviewing a Potential Informant Who is Not a Suspect

Before interviewing a potential informant who is not a suspect, investigative efforts should be

made to determine if the informant has any police record and, if so, if it could have any

bearing on the reliability of the information provided.

X. The Arson Suspect

In some arson investigations, a prime suspect may emerge and investigative efforts will be

Chapter 19: Arson and Explosives Investigation

Swanson: Criminal Investigation, 13e

IM-19 | 11

focused accordingly. However, in most cases, a number of suspects emerge, and merely

XI. Photographing the Arson Scene

A. Still Photography

Photographing a fire scene can be a challenge. Adverse conditions—poor lighting, time

B. Video Recording

Although the average fire investigation does not require video recording, it should be done if

the investigator reasonably believes that the case will involve litigation.

XII. Explosives Investigation

Under the investigation definition, an explosion is a physical reaction characterized by the

A. Know Your Explosives

Alfred Nobel invented dynamite by combining nitroglycerin with sodium carbonate and

B. Computerized Tomography (CT)

One method used to identify explosives is a CT scan. The “CT” stands for computerized

C. Sniffers

Chapter 19: Arson and Explosives Investigation

Swanson: Criminal Investigation, 13e

IM-19 | 12

Not all explosives detectors rely on the sense of sight. Some are called “sniffers” but do not

D. Types of Explosions

There are two major types of explosions: mechanical and chemical. In mechanical

XIII. Improvised Explosive Devices (IEDs)

An improvised explosive device (IED) is a combination of items or components that are neither

designed nor produced to be used in conjunction with each other but, when placed together or

assembled, constitute a mechanism that has the capability of exploding and causing personal

injuries and property damage.

A. Basic Components of the IED

IEDs have two very basic components, the main charge explosive and the fuzing system. The

B. The United States as a Target of IEDs

One of the most recent cases of the use of IEDs in the United States occurred in Boston,

Massachusetts on April 15, 2013. On this date at 2:50 p.m. two IEDs were placed in close

Chapter 19: Arson and Explosives Investigation

Swanson: Criminal Investigation, 13e

IM-19 | 13

C. Investigating the Explosion Scene

The objectives of the explosion scene investigation are no different from those for a regular

D. Locating and Identifying Articles of Evidence

Investigators should locate, identify, note, log, photograph, and map any of the many and

varied articles of physical evidence. Because of the propelling nature of explosions, the

XIV. Suspicious Packages and Letters

The following are precautions that should be followed when encountering a suspicious package

or letter:

• If delivered by carrier, inspect for lumps, bulges, or protrusions, without applying pressure.

A. Use of Robotic Devices in Moving and Destroying Dangerous Objects

Because handling suspicious packages can be quite dangerous to law enforcement personnel,

they have increasingly resorted to the use of robots to move and destroy such objects.

B. Terrorist Bomb Threat Stand-Off

Law enforcement officers should be aware of what the bomb threat stand-off distances are in

XV. Connecting the Bombing Dots

Chapter 19: Arson and Explosives Investigation

Swanson: Criminal Investigation, 13e

With the passage of the Homeland Security Act of 2002 and the movement of the U.S. Bureau of

Alcohol, Tobacco, Firearms, and Explosives (ATFE) to the Department of Justice (DOJ), U.S.

attorney general John Ashcroft—in his August 2004 memorandum to the heads of the Federal

XVI. Sharing Intelligence Globally

The International Bomb Data Center Working Group is a collaborative body of bomb data

centers and recognized government agencies focused on the efficient and effective sharing of