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Forensic Science: Forensic Evidence in Arson Cases: Part I

NCJ Number
Criminal Law Bulletin Volume: 28 Issue: 6 Dated: (November-December 1992) Pages: 554-561
E J Imwinkelried
Date Published
7 pages
To overcome difficulties associated with arson investigations, fire department investigators and crime laboratory analysts have intensified their efforts in arson cases to provide forensic evidence for arson prosecutions.
In many cases, the key determination by an investigator is identifying the fire's point of origin. Several factors must be taken into account in fixing the fire's point of origin: location of the apex of the V-shaped pattern; location of the lowest level of burn; point of deepest char; area of greatest damage; size of squares in "alligatorized" or "checked" wood; presence of small cracks in nearby glass; spalling of concrete; direction of light bulb distending; trails found on premises; and location of smoke deposits on walls. Once the fire's point of origin is identified, the investigator and laboratory analysts can isolate the fire's cause. Clues the investigator can evaluate to determine the fire's cause include smoke color, flame color, and odors present at the fire scene. Field chemical tests can be employed to analyze physical evidence from the fire scene. In any arson case, the investigator must ultimately determine if the fire was deliberately started. The following may indicate arson: signs of forceful entry into the structure; indications that another crime was committed on the premises; evidence of efforts to impede firefighter access to the building; windows left open, holes bored in walls, or interior doors tied open; removal of valuable property from the premises shortly before the fire; tampering with gas lines or electrical appliances on the premises; burglar alarms or sprinkler systems rendered inoperable; blinds or shades pulled down to obstruct the outside view of early fire stages; indications of the use of timing devices; multiple points of origin; and presence of unusual accelerants.