Wednesday, January 7, 2009

Toolmarks and Bombs

by Andrea Campbell

Almost every crime involves a tool. Shovels move dirt when evidence is buried, crowbars are handy for breaking into door frames and safes, screwdrivers sometimes force open windows, pliers help make bombs, and bolt cutters clip through fence. The tools used in executing crimes make scars, scrapes, dents, chips, and grooves, and these marks can be traced back to
the source just like striation marks on bullets or the ridges found on fingertips.

Police look for objects bearing toolmarks, photograph them, and, if movable, submit it to the lab. It’s not uncommon for investigators to saw off pieces of door frame, turn in small safes and locked drawers, or bring in bits of metal which may have come from the tip of a knife or the claw-side end of a hammer.

Then when a suspect is identified, they get a search warrant for his home or car and try to match up any found tool with its marks, because every tool is unique. N
o matter how well a tool is forged and polished, under microscopic scrutiny, one can see minute defects or marks on its strike- or cutting-surface. Plus, slight chips or faults as the result of hard employment are produced each time the tool is used. In Florida, a firearms examiner with the Metro Dade Crime Lab in Miami identified a knife used to make a stab wound. He compared the striations left by the knife blade on bone and cartilage on the victim’s sternum.

To compare toolmarks, the examiner reproduces test marks in a manner similar to “the unknown” crime-scene marks, and then he compares the characteristics of each, looking for a match. In essence then, the marks are duplicated and carefully compared.

Tools can also be a source of trace evidence, carrying on them tiny bits of hair, fiber, paint, and soil. And for its last evidentiary significance, toolmark examiners are qualified to make fracture matches—evidence that puts together a small broken fragment in a match to its whole.

For example, a series of bank robberies on night-deposit boxes was committed using hammers, crowbars, and screwdrivers. The method of removing the boxes was pretty clear, but that was all detectives had and nothing much happened. One night though, an investigator found a tiny piece of broken metal which police held onto as a clue. Later when several suspects were identified, a search warrant was obtained, and police collected broken screwdrivers among the suspects’ tools. The broken metal tip saved from the crime scene earlier, perfectly matched one of the broken screwdrivers found in their possession, and the toolmark evidence was enough to put that gang away.

Explosives, Bombs, and Fire

Evidence collection after a bombing or fire is chaotic, dangerous and difficult. Sometimes K-9 units may be used to sniff out explosives. Certain retrieval robotic units may be employed where the danger of future detonation is possible. Fire evidence is generally collected and put into clean, unused paint cans. Even the most seemingly insignificant fragments may prove helpful. Investigators look for blast-cap fragments, fuses, detonating wire, duct tape, cotton, steel fragments, samples of unexploded materials, and even fertilizer. An important clue to an airplane crash over Locherbie, Scotland, was a small fragment, no bigger than a fingernail, but it was evidence of a detonating device.

Laboratory findings in bombings can include:

• What type of explosive was used, possibly with the aid of a manufacturer's chemical signature, certain inert but identifiable chemicals in various explosives.

Where the explosion or fire took place.

• Identification of triggering device.

In Utah in 1985, a man killed two people with bombs and a third went off in his own car. After thinking the man might have been a victim, soon the trail of evidence led back to him. A workshop in his house proved to be the location where the bombs were constructed—items were matched to crime scene evidence—and sales people remembered selling him some of the supplies that later became parts for the bombs.

Detailed technical information regarding explosive devices is collected, plugged into the computer, and distributed via national databases. This helps authorities identify serial bombers, the sophistication of the explosive devices being used, and the need for a uniform procedure. The FBI has a Data Bomb Center and the Bureau of Alcohol, Tobacco and Firearms houses an Arson and Explosives National Repository.*


Leah said...

I didn't realize until I started watching ID that even trash bags and tape can be traced back to its original source. We've come a long way.

A Voice of Sanity said...

'Matching' items like trash bags and tape is a dubious sort of science at best. It is better used to eliminate something than to identify it. The FBI's bullet lead 'matching' technique has been shown to be without any scientific foundation despite being the only evidence used to convict in a number of cases. The fallout from this failure continues.

See for a rundown on this.

Andrea Campbell said...

Dear A Voice of Sanity,

I read the article you referred to and it is a tragedy that Kulbicki's case was tainted. What your reference proves however, is that 1.) The FBI disallowed any further bullet weight testing, 2.) that the system failed with respect to hiring someone who was either ill qualified or delusional. I see the mission of forensic science as this: to study evidence in a scientific manner, yes, but to have the best people working in the lab who will work fairly and in an unbiased manner. Bullet striation evidence is a valid method of determining the providence of the ammunition to a gun. The man who processed the evidence was neither qualified nor unbiased—and that is the rub.

Forensic science labs today are overwhelmed and underfunded. There is no true standardization. But for every Kopera that affects the system, there are thousands of cases adjudicated correctly.

So the mandate that we should have going into a new year, a new presidency and a new administration is to fund the state and municipal labs and make sure that the technicians hired are qualified and dedicated to the truth that science brings. The tenets of science are unbiased testing—not knowing the suspect or the case. That has to remain.

Thanks for your comments.

A Voice of Sanity said...

Actually the FBI had to be forced, kicking and screaming, to discontinue the use of this technique. Further, they resisted doing anything to notify the attorneys for those convicted by this method that it had been proven incompetent. Finally, after a great deal of effort, they did send out information admitting it was scientifically invalid. I believe to this day there are people in prison whose cases have not been overturned despite the fact that this was the only evidence of guilt offered.

I agree with you that the other method, bullet striation evidence, is a valid method but it needs to be performed by a conscientious and objective technician and not a friend of the police. Also, standards must be set and met.

There is no scientific basis for 'plastic bag matching' or 'tape matching'. We need good science based on good research and not junk passed off as science. Where are the statistical studies which are the essential core of such methods? Nowhere to be found.