Much to do following Boston Marathon explosions
The science of working a terrorist bombing incident really is quite interesting. After the victims have been cared for and evacuated from the scene, it is time to start processing the crime scene for evidence.
In Israel, I am told the whole scene of a bombing is processed and cleaned up in the matter of several hours. This is done to minimize the psychological effects of a bombing. We in the U.S. on the other hand, do painstaking scene processing because when a suspect is caught, the evidence and scene processing must stand up to the legal tests in our courts.
First and foremost the area will be photographed and videotaped. Police investigators will take scene photographs and videos after the fact, but some of the best evidence will be taken from other sources. The police also will have to measure and diagram the scene for later reconstruction in court if necessary.
Surveillance videos in area stores and businesses, spectator videos and pictures, aerial shots from helicopters, and general media photographic and video images will be analyzed for clues. The images will be painstakingly examined to identify the suspect(s) involved.
Witness statements will be collected by officers by canvassing the area. Spectators and bystanders in the area will hold an important key to the investigation. Investigators must always assume, in any investigation, that “somebody saw something” and that is how they have to conduct their interviews.
The problem in Boston will be locating people who saw something before they head back to their homes all over the nation. It will be incumbent on witnesses with information, videos or photos to call tip lines if they think they have information.
Cellphones will play a key role in this case. Cellphone companies must always know where calls are made from, so cellphone companies can bill for the customer appropriately. Therefore using cellphone company records, law enforcement will be able to ascertain what phones were making calls and in some cases what phones were in the area around the time of the bombing.
AP Photo | Charles Krupa
The air blast is caused by the shockwave created by the rapid chemical reaction that gives off so much energy. The air blast, propels pieces of the bomb and other items around the detonation outward as projectiles called shrapnel.
Injuries from shrapnel are the most obvious at the scene, producing visible wounds to the victims. Air blast injuries are not as obvious. Air blast injuries effect less dense or less solid organs in the body. Air blast injuries primarily effect the ears, lungs and central nervous system, including the brain.
The clothing from bomb victims often contains valuable evidence from the blast. For this reason investigators must retrieve the clothing worn by the victim as well as shrapnel removed from the victims’ bodies, from the hospital.
This evidence might include the chemical compounds of the detonated material. Other evidence taken from victims might show the bombers intent to inflict injury and death. Items such as roofing nails in the Atlanta Centennial Olympic Park Bombings in 1996 or ball bearings in Boston contained in the explosive device act as lethal shrapnel and clearly show a bomber’s intent.
Incidentally a .357 magnum handgun bullet flies at around 1,400 feet per second. The muzzle velocity of a .223 rifle round — which is a common assault rifle round — is about 3,650 feet per second. Shrapnel from a bomb starts out at approximately the same rate as the .223 rifle round and increase depending on the explosive used. The detonation velocity of military C-4Â — or plastic explosives — is 26,400 feet per second.
The point here is that when you see your favorite Hollywood action hero running and diving away from a fiery bomb blast, it is impossible. By the time a person could process seeing or hearing an explosion the shrapnel from the blast already has hit them.
That being said, I once saw an interesting T-shirt on a bomb technician who had responded to the scene of a suspicious package. It said: Bomb Squad — If You See Me Running, Try To Keep Up.
Another very interesting fact about bomb detonations is the evidence and components of the bomb are often times right near where the bomb was detonated. Conventional wisdom would hold that everything involved with the blast would be blown away form ground zero, and indeed it initially is, during what is called the positive pressure pulse. During this phase of the explosion, solid materials are transformed into a gas in 1/10,000th of a second, a shock wave or air blast is sent out from the explosive.
Immediately after the positive pressure pulse, there is a negative pressure pulse, which is caused by the inward rush of displaced air. This causes a vacuum effect, which can pull pieces of the triggering mechanism, which is an important component of the bomb to identify the bomb manufacturer, back into the area of the initial blast. This negative phase if less powerful, but lasts much longer than the positive phase.
This phenomenon is demonstrated in the video of the Boston Bombing. If you closely watch this video of the event, there is a lamp post near the middle of the screen. To the left of the lamp post there is a yellow balloon that blows out and is pulled back into the blast area. Similarly there is a white over red international flag, which is blown out and then are pulled violently back upright in the same area of the screen.
I have confidence in those investigating this terrorist incident. Somebody saw something, somebody knows something or evidence will point in the right direction, but those responsible for this act of murder will be caught.
Please remember this latest act of terrorism and those that came before it the next time you are delayed at airport security or asked to put something back in your car at a large public event you attend. Those delays and requests are necessary for our collective safety.
Lock it up, don’t leave it unattended, be aware and watch out for your neighbors.
Rich Kinsey is a retired Ann Arbor police detective sergeant who now blogs about crime and safety for AnnArbor.com.