Documents
Resources
Learning Center
Upload
Plans & pricing Sign in
Sign Out
Get this document free

The Case of the Disappearing Fingerprints - usaschool.us

VIEWS: 8 PAGES: 3

									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.

								
To top