Forensics Q&A: Explosives Crime Scene Investigation

By Kristy Lahoda | @KristyLahoda

Disclaimer: The information provided in this post should not be used for malicious intent unless it is in the form of crime writing. The author is an explosives expert, not a crime scene expert. While every attempt was made to ensure the accuracy of this information, for security purposes, some details may have been withheld.

QUESTION: My antagonist is a juvenile delinquent who set off a pipe bomb with the intent to destroy property. What would the bomb scene investigation look like?


ANSWER: There should be three phases of the investigation: outside investigation, control and coordination, and inside investigation.

Outside Investigation

First responders have the initial responsibility. Above all else, safety and security must be ensured. After assessment, a call for backup may be warranted. If the scene is unsafe, the first responder must not only wait until the scene is made safe, but must also ensure that the scene is secure for the safety of others. The last casualty from the bombing of the Alfred P. Murrah federal building in Oklahoma City was a nurse who wanted to help the injured. She passed away because a computer monitor fell on her from one of the compromised floors above. Once the scene is safe, rescue of victims is performed.

The crime scene must be secured. This involves establishing an inner security perimeter by placing crime scene tape around the scene. Hazards should be identified and removed or mitigated. Sometimes it is not initially known if the explosion was the result of a bomb, so a call to the bomb squad might be necessary in order to check for secondary devices. A structural engineer may need to be called to check the structural integrity. Other potential hazards that must be taken into account may include fire, hazardous materials such as asbestos and carbon monoxide, utilities such as electrical, natural gas, and ruptured water pipes, debris such as metal and glass, and blood-borne pathogens. If there is fire at the bomb scene, firefighters should use only enough water to quench the fire because the evidence could be washed away. Also during this phase the first responders should ensure that evidence that might be removed from the scene is properly preserved. Witnesses should be located and interviewed and license plates checked—the perpetrator might be among the crowd. The outside investigation is not just a phase of the crime scene investigation, but remains ongoing until the case is solved.

Control and Coordination

Control and coordination takes place once the scene is secure. This phase involves compiling the information obtained from the outside investigation and making it available to the inside investigation. The people operating in this capacity direct investigative endeavors by acting as the filter for incoming and outgoing information by briefing and debriefing. They are responsible for resources acquisition and allocation. A command post is set up near the crime scene, but at a distance so as to not interfere.

Inside Investigation

The inside investigation may occur within a building or outside. The term “inside” is used to indicate that this phase of the investigation is generally confined to the crime scene itself. It is like piecing a puzzle together by collecting physical evidence. The inside phase may need to be moved to a secure area if, for example, the structure is unstable.

The crime scene investigator should meet with the first responders at the command post to learn what actions have been taken. Are there are any victims? Is there any relevant information from witnesses regarding the scene? Are there any known hazardous materials present? Is there any physical evidence already located? They should establish perimeters. The inner perimeter should encompass the blast area including where the evidence is present. The command post should be set up at this boundary and should be determined by multiplying 1.5 by the distance from the epicenter to the farthest piece of evidence located. The outer perimeter is the distance at which investigators want to keep people away not affiliated with the crime scene.

The investigator needs to conduct a walkthrough for observation purposes to identify the “nature of the explosion” and possible evidentiary items. The process of documenting the scene may commence during this stage.

After the walkthrough the team lead should come up with an investigative plan for the scene such as contamination prevention. Contamination of the scene with trace evidence is a real possibility. The investigators should wear Tyvek or laundered clothes and shoe coverings. Care should be taken to avoid stepping on potential evidence and destroying things like shoeprints, tire treads, etc.

The team lead should brief the team and assign specific tasks, ensure that team members are wearing proper protective clothing, and provide reminders not to forget the basics—to be on the lookout for fingerprints, shoeprints, tire treads, tool marks, and trace evidence such as DNA, blood, fibers, suspicious packaging and wrappers, etc. A member should be assigned to swab explosive residue.

A number of steps take place during the inside investigation including establishment of a team lead, evidence identification, documentation, collection, and preservation, and the performance of a final survey.

Establishing a Team Lead

A team lead should be chosen to serve as a liaison between the inside investigation unit and the command post, to formulate an action plan such as assigning investigators/scientists to certain tasks in order to cover all bases, arrange for the command post to obtain essential equipment, and help to maintain the morale of the unit. Two essential questions should be asked. What happened? How did it happen? This is the objective of the crime scene search.

Documentation, Identification, Collection, and Preservation

The scene is documented. This includes photographs, sketches, and notes. Photographs of the scene should be taken to include an overall perspective. Once evidence is identified, such as pieces of an explosives device: the possible container, fuzing mechanism, and filler, it may also be documented. Key evidentiary pieces should be photographed individually. The photographer should coordinate with the sketch artist. Photographs of every individual item are not required, but should be taken prior to moving the evidence if that piece is considered vital to the investigation. Evidence custodians collect, package, and label the package. Chain of custody is important during this step, thus an evidence log should be maintained.

Final Survey

A final walkthrough of the crime scene is performed to verify completion of crime scene evidence search, documentation, and processing. Recovery of all equipment used should also be completed at this time.

There are multiple investigations occurring during an explosives crime scene investigation. The outside investigation and inside investigation are linked together through the control and coordination unit. This connection is important to bring the puzzle pieces together for both phases. It is the responsibility of the inside investigative team lead to keep up the team morale due to the nature and tedium of the investigation. This is one of the most important jobs. When the crime scene investigative team grows weary or emotionally unstable, mistakes are made.

Source: Thurman, James T. Practical Bomb Scene Investigation. Boca Raton: CRC Press, Taylor & Francis Group, 2006. 

For more information on these topics, stay tuned for the installments in the upcoming months of Forensics Q&A!

Kristy Lahoda, Ph.D., is an explosives analyst contractor in a crime lab as well as a science content editor for a major educational publishing company.  She writes Christian forensic suspense and discusses forensics on her blog called Explosive Faith.  You can follow her on Facebook and Twitter.

If you have a forensics question for Dr. Lahoda that you'd like to see answered on the QueryTracker Blog, send your question via Carolyn Kaufman using the email link under Contact Us in the right-hand column of the main QTB page.