You may have heard about the Pan Am Flight 103 crash over Lockerbie, Scotland. A well-maintained Boeing 747 seemingly dropped out of the sky on December 21, 1988. Within a week of the crash, the investigation team announced they had found traces of explosives and determined that the aircraft had been brought down by a bomb. With the help of forensic scientists who specialize in arson and explosion investigation, the team was able to reconstruct both the type and exact location of the bomb responsible for the crash.
How exactly does the wreckage of a fire or explosion tell the story of the crime? It turns out that both the burn pattern and the chemical residues that are left behind can provide valuable clues about the event. Specifically, the location of the most intensely burned remnants provides important information about where the event started.
In the case of a fire, investigators must look for the most intensely burned debris to find the origin of the fire. In the case of an explosion, there will also be a crater at the site of the blast. With either type of event, chemical residues can tell how the event happened. For example, was kerosene used to make the fire spread quickly?
Fire and explosion investigation is not without its challenges, though. The following are just a few elements that make the job of an arson and explosion investigator more difficult:
– The perpetrator has lots of time to plan and execute the crime, meaning s/he has generally left the scene long before investigators arrive.
– The event itself destroys evidence.
– Evidence such as kerosene and gasoline, if it survives, can often evaporate within hours.
– The origin of the event may be obscured by debris from subsequent incidents, such as floors collapsing.
Arson and explosion investigation is the process of analyzing the charring and chemical residue (if any is left) on the debris found at the crime scene to perform the following tasks:
– Determine whether the event was accidental or intentional.
– Identify relevant chemicals found at crime scene.
– Reconstruct how the arson or explosion was started.
In rare cases, investigators may get a suspect promptly. In this case, they can analyze the suspect’s clothes and posessions to try to match residues or other paraphernalia to the crime.
To get the most possible information, it is important for the arson and explosion investigator to begin the investigation as quickly as possible. Fire accelerants and explosive powders often evaporate within hours or days of the event. Investigators perform the following tasks at the crime scene:
– Locate the origin of the fire or explosion.
– In the case of fire, look for devices and containers used to ignite and/or spread the fire.
– In the case of explosion, look for detonating mechanism and use dogs or a vapor detector to find residue.
– Look for accidental causes as well as evidence of foul play.
– Make notes, draw sketches, and take photos of the evidence.
– Pack evidence in airtight containers to prevent evaporation of residues.
When the evidence has been recovered from the crime scene, work begins in the lab to reconstruct the event that produced the destruction. Arson and explosion investigators analyze residues to get information about the accelerants or explosives involved in the crime . They often perform carefully planned control experiments to try to recreate the crime, especially when they need to test different hypotheses about the events.
The arson and explosion investigator must take detailed notes during every step of the process. These notes are used to write a full report about the analysis and its conclusions. If the evidence from the analysis is used in a case that goes to trial, the arson and explosion investigator may be required to testify in court about the work.
Arson and explosion investigation is an inspiring field of forensic science that will continue to provide exciting career opportunities well into the future.
About the author: Emily Nelson earned an M.S. in Electrical Engineering from the Massachusetts Institute of Technology before beginning her career as a science writer.