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The Case of the Disappearing Fingerprints The murder was a detective's worst nightmare. A three-year-old girl had been abducted from her neighborhood, sexually molested, and brutally killed. Police were sure that a family acquaintance was the killer—in fact, initially the suspect had confessed, but later he recanted. Investigators were desperately seeking hard evidence to link the suspect to the dark and sinister crime. As results came in from the forensics lab, Knoxville Police Department Specialist Art Bohanan felt frustration wash over him. The suspect's fingerprints were all over the inside of the car thought to have used in the abduction. But there was no trace of the little girl's prints. It was not the first time Bohanan had run up against this particular brick wall. In a similar case several years earlier, witnesses testified that they had seen the child in the suspect's car—but no prints from the missing child could be found there. What was it about children's fingerprints and cars that conspired against Bohanan? Checking with others in the department and then with other law enforcement agencies, Bohanan found little to go on. The Federal Bureau of Investigation (FBI) could offer nothing. Scotland Yard had no answers. The Israeli police had not observed it, either. Forensic scientists had done little research on the fingerprints of children, because children were rarely crime suspects. We think the kids' fingerprints are still there, but the current technologies used by police just don't detect them. Knoxville Police Detective Art Bohanan lifts a child's fingerprints off a car as his granddaughters watch. He sought help from ORNL in explaining why childrens' fingerprints vanish faster than adults'. Unfortunately, more and more of them seemed to be turning up as crime victims. The question, Bohanan decided, cried out for an answer. Though not a scientist by training, Bohanan devised an experiment. He had children and adults handle two cases of Coke bottles. One case of the bottles he placed in his cool basement as the control group; the other he put in the back seat of his police car to simulate realistic field conditions. Each day for the next month, Bohanan removed a bottle from both cases and dusted them for fingerprints. He found what he had suspected all along: while the adults' prints remained, the children's prints began disappearing almost immediately; soon they were gone altogether. He repeated the experiment for an entire year, and although the children's prints lasted longer, they still vanished before those of the adults. Now that he had proof of what was happening, he turned to science—he turned to ORNL—for help understanding why. To tackle the problem from multiple angles, ORNL Director Alvin Trivelpiece assembled a group of scientists from a variety of disciplines. To tackle the problem from multiple angles, ORNL Director Alvin Trivelpiece assembled a group of scientists from a variety of disciplines. As they discussed the case, Michelle Buchanan, an analytical chemist in ORNL's Chemical and Analytical Sciences Division, had a hunch. "It occurred to me that it must be a difference in the chemical composition of the prints," Buchanan recalls. "We decided to use gas chromatographymass spectrometry—GCMS—to analyze the chemical composition of children's fingerprints." Knoxville Police Detective Art Bohanan and ORNL's Michelle Buchanan examine fingerprints. Buchanan's research suggests that children's fingerprints don't last as long as adult fingerprints because of a difference in chemical composition. In that instant, the investigation into the girl's murder changed dimensions. It moved out of the typical police crime lab, with limited scientific equipment, and into the national laboratory, where researchers work on the cutting edge of science. Though beyond the reach of a typical police lab, this experiment, too, began simply enough. "We took small vials and put a couple of milliliters of rubbing alcohol from a drug store in each one," Buchanan explains. "We had a group of adults and the children shake the vials between their fingers. The alcohol extracted a small amount of the chemicals off the surface of their skin." Buchanan and her colleague Keiji Asano now had the samples they needed for GCMS analysis. Working with the ORNL chemists was a group of undergraduate students, who participated in the project as part of the Science and Engineering Research Semester program. Over the past few decades, gas chromatographymass spectrometry has become the workhorse of the analytical chemist's laboratory, examining unknown compounds to extract precise information about their makeup. The students injected samples of the dissolved chemical compounds into the GCMS. After the chemicals vaporized there, they were separated on a heated capillary column by clinging to the viscous coating on the narrow column. Lighter, more volatile elements came through first; heavier elements held on longer. By combining gas chromatography with mass spectrometry, the chemists learned which compounds were present. By hammering the molecules of each substance in the sample with electrons, a positive charge was given to each molecule. During this ionization process, most of the ions fell apart to form a number of fragment ions. The ions were then sorted in the mass analyzer, producing a spectrum that identified each compound, much like a fingerprint identifies an individual. When the researchers looked at the printouts, they were amazed. The data from the experiment could be laid down in two neat piles: children in one, adults in the other. The children's prints had far more of the compounds known as fatty acids. The adult prints also contained fatty acids but at much lower levels. The adult prints, however, were observed to contain larger quantities of fatty acid esters, which are less volatile than the fatty acids that are predominant in children's fingerprints. The difference in the fingerprints was like the difference between footprints of gasoline and those left by motor oil being tracked across the floor at a service station: although chemically similar, one evaporates in moments, the other hardly at all. Now ORNL researchers could explain Bohanan's observation. In a hot car, the lighter fatty acids in children's fingerprints were volatilizing—just going away. When police dusted for prints with powder, there was nothing left for it to stick to. From the perspective of pure science, they had answered the question. But from the perspective of applied science—the kind of science that saves lives—they had raised more questions than they'd answered. ORNL researchers are developing new chemical markers that make invisible prints fluoresce under hand-held lights. "We think the kids' fingerprints are still there, but the current technologies used by police just don't detect them," says Buchanan. Based on the results from these preliminary studies, organic chemists at ORNL are now trying to develop new chemical "markers" that police can use to make invisible prints fluoresce under special hand-held lights. The search for an identifying compound has opened a second door. The researchers have detected a wide variety of substances in prints, including cholesterol and nicotine. They are currently investigating the potential of identifying trace components in fingerprints that can distinguish among individuals. Says Buchanan, "This raises the possibility that components in fingerprints could yield a profile of the suspect like 'female, smoker, diabetic, cocaine user.' " Soon, these tools may help police and the FBI unlock vast amounts of evidence now hidden at the scene of a crime—and help Bohanan and his colleagues bring killers to justice.
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