Consistency of Evidence

Unless there is a direct admission of guilt, a definitive photograph or video tape showing the crime, or irrefutable eyewitness testimony, it is difficult to convict an arsonist. More traditionally, it is necessary to make the determination of arson by considering the consistency of the physical evidence, witness statements, and factors that support the motivation, opportunity, and means for a potential criminal. As fire investigators, particularly in the private sector, it may not be necessary to convict or even identify the potential arsonist. It may be more important to simply classify the fire as accidental or intentional, and to have sufficient evidence to do so on a “more likely than not” basis. There are occasions in which evidence is insufficient to meet the higher standard for criminal conviction (beyond a reasonable doubt), but sufficient in civil proceedings to deny insurance claims because of arson and intent to defraud.

If arson is suspected, the consistency of evidence related to the fire characteristics should be evaluated for a number of issues including:

• Burn pattern compared to reported fire characteristics and progression
• Accelerants in unexpected locations

• Ignition and propagation times compared to witness reports
• Evidence of fluid leakage from vehicle in its usual parking area

Similarly, the consistency of evidence related to vehicle characteristics should be evaluated for a number of issues including:

• Operational condition of ignition/steering wheel lock
• Missing accessories
• Evidence of forced entry
• Report of damaged bodywork and vehicle defects
• Inventory of ignition keys
• Remnants of key evident after fire
• Service records indicating that operating condition was consistent with owner statement

• Vehicle service history relative to fire origin
• Condition of engine internals, including lubricants

Technology can be used for differentiation of potential fire causes. Some of the analytical tools used for fire and arson investigation include

• On-board computer records, which are stored in the memory of modern vehicles can sometimes be used to assess the operational condition of the vehicle prior to an incident, including evidence of recent crash impulses or fault codes that may indicate engine operational problems or trauma. Extracting and interpreting these data may require specialized equipment and expertise. Of course, if the fire was extensive, such records may have been lost.
• Gas chromatography can be used for chemical identification of possible accelerants that may remain in trace amounts after the fire. Proper sample gathering and handling must be followed, with analysis by a reputable laboratory. As previously mentioned, caution must be exercised in the interpretation of results; a positive test for accelerants, such as hydrocarbon fuels, may not indicate a definitive cause of fire [1].
• Oil analysis can be conducted by a laboratory to evaluate the metal content in a sample of engine or transmission oil. Such analysis may also be used evaluate the oxidation level of the oil, that may be indicative of internal overheat from poor operating condition. Note that full scale vehicle burn tests have shown that even extensive fires are not likely to deteriorate oil and transmission fluid [2].
• Material and metallurgical testing and analysis can be conducted to determine the cause of failed material (for example that may be indicative of forced entry or pre-fire steering column lock damage), the temperature that a metal or polymer attained, or other qualities that may be important to fire cause determination.

To learn more about a technique some suggest can be identify the last key used in a lock (key pathway analysis), click here.

References

1. Sutherland, D., et al., “GC/MS/MS An Important Development in Fire Debris Analysis,” Fire and Arson Investigator, October 2000.

2. Hrynchuk, R., “A Study of Vehicle Fires of Known Ignition Source,” IAAI Alberta Chapter, January 1983.