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But for all its glamour and promise, DNA testing is not the technology that truly excites forensic scientists--or the people who make TV dramas. What thrills them most is the hardware--the scopes and scanners and mass spectrometers that allow investigators to peer with remarkable precision into any given piece of evidence.
For example, one of the jobs criminal investigators routinely perform is testing for gunpowder on suspects' hands. In the past, this was a surprisingly low-tech chore, involving melting a glob of paraffin in a pot and painting it onto the fingers and hands. The wax was then peeled off and treated with chemicals that react to gunpowder traces. If the chemicals turned up positive, you had your shooter--unless, of course, the chemicals were reacting with urine, bleach or fertilizer, which had a nasty habit of yielding identical results.
Today most forensics labs that conduct the test rely instead on scanning electron microscopes. Just touch a bit of tape to a suspect's hands, place it under the scope and hit it with a stream of electrons. The elements in gunpowder give off distinct X-ray signatures, and if they are there, the electron beam will spot them. The drawback? "You don't get to see the terror on people's faces when you pour hot paraffin on their hands," says Fischer. "I think it encouraged some people to confess."
Equally impressive are the new gas chromatography and mass spectrometry machines. To test a bit of evidence whose chemical composition is unknown, investigators place it in a gas chromatograph--essentially a high-intensity oven--where it's vaporized. The resulting gas is funneled into a coil-shaped structure lined with chemicals that cause the components in the gas to exit at different rates. These components are then sorted by atomic weight and converted into a graph. Investigators then compare the readout with a reference library, determining what the evidence is made of.
The problem with gas chromatography and mass spectrometry, however, is that in order to analyze evidence, you have to destroy it--which means investigators have to get the test right the first time, or the perp might walk. A new laser ablation spectrometer under development could solve that problem by etching off only a tiny slice of a sample with a needlelike light beam and cooking it in a plasma furnace equipped with a mass spectrometer especially sensitive to trace elements. Similarly, researchers at California's Lawrence Livermore National Laboratory have shown that a synchrotron radiation device can bounce a beam of infrared energy off a piece of evidence and analyze the spectrum of its reflection without damaging the sample. Researchers are also trying to use infrared hardware to analyze the composition of the oils in fingerprints, which would allow suspects to be identified not just by their print patterns, but by their chemistry as well.
Sometimes the best prints don't exist in the real world at all. In some forensics labs investigators can take digital snapshots of a fingerprint on, say, a colorful soda can, then manipulate the image to float the print off the can. "We cancel out the background," says Narveson, "which gives us a lot better chance to capture the detail of the print."