I started reading up on what it takes to work a post-blast crime scene, and though I found a lot of good information, I know it didn’t begin to scrape the surface. I guess that’s the wrong metaphor to use, because after a bomb goes off, there isn’t much surface left. Can you imagine going to the scene? There are tons of material called gross physical evidence. Most of the time you don’t know what you’re looking at, even though nearly everything is potential evidence. The debris is shredded, cut, spun, blended, burned, ruffled and any other adjective describing destruction like nothing you’ve ever seen.
Classifying and Typing
A low explosive is typically heat-sensitive material that burns rapidly, about 1,000 feet per second. High explosives, on the other hand, are considered detonations — decomposition of molecules that are forced through a shock wave at about 10,000 feet per second. The difference between the two is significant in helping to understand what has happened; low explosives are more likely to cause a fire than the shorter impulse time associated with high explosives.
Explosives Differ in Other Ways Too
Low explosives need a housing or container, because burning produces the gases needed for expansion. High explosives give off their energy as the result of a detonation or shock wave and can be out in the open.
The activator of the fusing system is put into three basic categories: 1.) time-activated, 2.) victim-activated, and 3.) command-activated. The first uses a time delay, the second is similar to a booby trap, and the third is set off manually, often using a remote-control device. According to GlobalSecurity.org, a person-borne suicide bomb usually employs a high-explosive/fragmentary effect and a command-detonation firing system -- a switch or button the suicide-bomber pushes to set off the blast.
Dr. Kirk Yeager, an explosives forensic scientist at the Federal Bureau of Investigation explainsit quite simply: A bomb consists of an oxidizer and a fuel. An explosion requires oxygen, provided by the oxidizer, and a fuel source, which can be as basic as sugar. A common oxidizer is ammonium nitrate, a primary ingredient of fertilizer. While bombs made with sugar and ammonium nitrate may be less potent than more advanced fuel sources, like TNT, the ingredients are easy to buy and legal to own. It’s interesting to note that the rapid oxidation in a bombing changes the colors of materials such as pipe or steel. (The 2004 Madrid train bombing is pictured above left.)
Working the Scene
A team will have a leader, a bomb technician, a photographer and sketch artist, and an evidence custodian. Depending on the size of the blast area, the team may be augmented by additional investigators.
The borders of a post-blast scene can be tremendous in size. Paul R. Laska, a retired crime scene investigator, says the lead investigator generally looks for the furthest item that can be identified as having originated at the point of the blast. A radius is established based on the distance of that item plus half again.
Often investigators will suit up in protective gear including shoe covers to avoid blood-borne pathogens. The scene is monitored for hazardous materials as well.
Collecting and Preserving
- The Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) has been collecting, storing and analyzing records on explosives and arson incidents since 1976.
- The FBI works on bombings related to terrorism.
- 1997 Omnibus Consolidated Appropriations Act, 18 U.S.C. 846(b), established a national repository for incidents involving arson and the criminal misuse of explosives.
- The U.S. Bomb Data Center (USBDC) is the sole repository and contains information on more than 180,000 arson and explosives incidents investigated by ATF and other federal, state and local law enforcement and fire investigation agencies.
According to the US Bomb Data Fact Sheet, which provides overall statistics and information such as event locations, bomb types used, and regional maps, contains the figures listed below. Explosives Incidents in the United States: In 2007: 2,772 explosives incidents, 60 people injured, 15 killed, and 633 referred for prosecution. In 2006: 3,445 explosives incidents, 135 people injured, 14 killed, and 745 referred for prosecution.