How It’s Done

Evidence That May be Collected

A detailed investigation of a blast site will reveal crucial clues to lead the investigation. By thoroughly documenting the condition of the scene, including any structural damage and injuries or fatalities, investigators can slowly piece together what occurred.

Fragments of an exploded device will often be left intact, including switches, wiring, timers and circuit boards. If the timer was made from a unique type of watch, for instance, that information could help narrow the search for who created the device or where it may have come from.

An investigator sifts through small pieces from an exploded IED

(Courtesy of NFSTC)

After an explosion, residue from the explosive that was used will be left behind. To identify the type of explosive used, investigators may use an ion mobility spectrometer (IMS), a handheld chemical detection device, to identify residues that may be present around the blast site.

For large-scale incidents, the area of investigation may be expansive. The bombing of the Pan Am Flight 103 over Lockerbie, Scotland in 1988 created the largest crime scene in the world. It stretched for more than 1,200 square miles. By painstakingly piecing together the wreckage that was found in this area, investigators identified trace amounts of explosives that helped confirm the incident was indeed caused by a terrorist attack. Two hundred seventy people died that day—259 on the plane and 11 residents of Lockerbie.

In addition to collecting physical evidence, video footage may be available from security cameras or from witnesses’ cell phones. Investigators will also interview witnesses and victims to gather crucial details.

How the Evidence Is Collected

If an undetonated device is located, it must first be rendered safe. A bomb should never be moved from where it was found because it could detonate. This should only be conducted by a qualified bomb technician. Safety is the primary consideration; damage to a structure can be repaired, but injury to a person could be life-altering or fatal.

To examine the type of explosive, bomb technicians use remote robotic equipment to take pictures of the device, or even to detonate the bomb. Robots are commonly fitted with a device that can shoot a high velocity jet of water into the device, disrupting it. The bomb squad technician can then move in to confirm the area is safe and law enforcement can begin an investigation.

A bomb squad technician may also use a portable X-ray tool to examine a suspicious package to determine if it contains an explosive. X-rays are commonly used in airports to examine luggage to ensure baggage does not contain explosive devices.

Before being transported from the scene, all physical evidence is photographed, packaged, placed into containers, labeled and secured. Evidence could even be lodged in the bodies of victims or a suicide bomber. The body can be examined via X-ray images and the evidence retrieved if necessary.

If a community doesn’t have its own specialized unit to handle explosives, it will have an agreement with a nearby bomb squad to handle these types of situations.

Who Conducts the Analysis

Several professionals may be involved in examining explosives evidence or a destructive device. A chemist who is specially trained examines items for explosive residues. This practitioner may work in concert with explosive device specialists who have knowledge of electrical components, expertise in device reconstruction and an understanding of post-blast damage.

In circumstances involving terrorist IEDs, the devices are analyzed by the FBI’s Terrorist Explosive Device Analytical Center (TEDAC). TEDAC is located at the FBI Laboratory in Quantico, Virginia. IEDs collected from around the world are sent to TEDAC for forensic examination.

How and Where the Analysis is Performed

Once a device is rendered safe, it can be analyzed like any other piece of evidence to search for leads regarding who was responsible for creating and deploying the device. If large fragments of the device are retrieved, DNA or fingerprints may be present that analysts can attempt to match to a suspect. DNA profiles are compared to records in the FBI’s national Combined DNA Index System database, “CODIS”. Learn more about DNA ▸

Post-blast explosive residues can be analyzed using a variety of techniques such as infrared spectroscopy, gas chromatography/mass spectrometry, energy dispersive X-ray analysis, Raman spectroscopy and other techniques. Learn more about drug chemistry ▸

Explosive devices can be searched against several national databases that are maintained to identify trends in the manufacture of explosives, and track bomb and device designs employed by serial bombers and terrorist groups. These databases include the FBI’s Terrorist Explosive Device Analytical Center, the ATF’s Arson and Explosives National Repository and the National Fire Incident Reporting System.

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