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On the cutting edge: Oak Ridge laser technique helps police build case
[June 9, 2006 Chattanooga Times/Free Press, Tenn.]


Next month, Court TV network will profile a case in which an Oak Ridge National Laboratory technique called laser-induced breakdown spectroscopy helped solve the murder of a 20-year-old Texas mother.

Laser-induced breakdown spectroscopy, or LIBS, is a pulsed laser focused on a sample. The resulting emissions can determine the elemental composition of various solids, liquids and gases.

"You look at 'CSI' and see (a technique) that is turnkey," said Dr. Madhavi Martin, an environmental scientist at ORNL. "I think this could do that."

In the Farmersville, Texas, case, partially burned wood at the outdoor crime scene was matched by the spectroscopy technique to wood at the suspect's home. The wood had identical elemental makeup, proving it came from the same tree.

The suspect, who had tried to burn victim Rachel Tolleson, was convicted and sentenced to death.

Since then, Dr. Martin has done work on bones from the University of Tennessee's Anthropological Research Facility, also known as the Body Farm, on a prosthetic knee replacement that is the subject of a lawsuit and on counterfeit currency.

"It's not my bread and butter," she said, "but it's kind of fun to work on something different." Dr. Martin's latest research is funded by the U.S. Department of Justice and ORNL's Laboratory Directed Research and Development program.

Tom Bodkin, a forensic anthropologist with the Hamilton County Medical Examiner's Office, said LIBS offers many forensics applications that have not been explored.

"You can analyze whatever you're looking at down to the atomic level," he said. "There is no lying there. You're presenting hard-core scientific information in the courtroom."

Before the Texas case, Dr. Martin was working on a LIBS project in which she was trying to show that different pieces of wood from different locations would have a different elemental makeup. When she was given 13 pieces of wood from the murder case, she was provided no background but only asked to test the wood. When she reported results of similar elemental properties in each piece to Dr. Henri Grissino-Mayer, a climatologist and bigeographer at the University of Tennessee who had given her the wood, he said it was good news.

When she asked why it was good news, since she was expecting different elemental properties in different pieces of wood, he explained the circumstances of the case to her.

"That's why I didn't tell you," Dr. Martin said Dr. Grissino-Mayer told her. "I didn't want you to be biased."

In their combined report, they said they could state with 99.995 percent confidence the wood was from the same place.

However, Dr. Martin said, a hearing still had to determine the admissibility of their report before it could be used in court. In the end, it was allowed, but didn't need to be used because the suspect, Moses Mendoza, had admitted his guilt.

Wayne Pickett, chief of the Farmersville Police Department, said although the police and FBI had a good video and written confession from the suspect, they continued to gather evidence in case he changed his mind.

"Everything coincided with his statement," he said, adding that the wood and other evidence made the eventual outcome a foregone conclusion even if Mr. Mendoza changed his plea.

Since then, Dr. Martin's spectroscopy tests on bones have shown, in addition to age, sex, ancestry and stature, that there are elemental differences between human and animal bones. There are also differences between carnivore, herbivore and omnivore animal bones. There are even differences in bone composition among the races, she said.

"At first, I thought, 'I hate to touch those bones.' It's kind of weird," she said. "But it's intriguing to see (the differences) in the first few experimental cases. It's a good area in which to do research."

Mr. Bodkin said LIBS offers "so many advantages" over an Inductively Coupled Plasma analyzer, an instrument currently used for determining the elemental composition of substances.

An ICP analyzer only tests solutions, while LIBS tests solids, liquids or gases, he said. In addition, an ICP analyzer only searches for those elements it has been programmed to search for, while LIBS searches for all elements in the periodic table, he said.

The LIBS also works quickly, Dr. Martin said. "You know (a substance's composition) in a few seconds."


http://www.spectroscopynow.com/coi/cda/detail.cda?id=13760&type=News&chId=7