Scientists have found ways to tease even more clues out of fingerprints' telltale marks - one in a string of developments that gives modern forensics even better ways to solve mysteries like the anthrax attacks or JonBenet Ramsey's murder.
For example, if a person handled cocaine, explosives or other materials, there could be enough left in a fingerprint to identify them, says chemist R. Graham Cooks of Purdue University in West Lafayette, Ind.
Progress in forensics comes from a combination of new techniques, like those involved in the anthrax investigation, and existing techniques, like those used in the Ramsey case, said Max M. Houck, director of West Virginia University's Forensic Science Initiative.
Improvements in genetic research allowed police to trace the anthrax used in the 2001 attacks to a specific flask of spores, the FBI said this week.
And while the killing of 6-year-old Ramsey attracted national fascination in 1996, it was only this year that prosecutors announced that a new series of tests pointed to an unidentified attacker, clearing family members of suspicion.
The testing technique in Ramsey's case was not new, Houck said. But prosecutors learned it could be relevant to their case in a 2007 West Virginia University course.
In the new fingerprint analysis method, police technicians armed with miniaturized mass spectrometers can spray a solvent on a fingerprint and detect compounds at concentrations as fine as five parts per million in droplets that scatter off the print, Cooks explained in a telephone interview. Five parts per million is equivalent to five ounces of chemical in 32 tons of material.
The testing method, discussed in Friday's edition of the journal Science, could be available in a year or two, Cooks said.
He explained that materials such as cocaine and military explosives tend to be hard to get off the fingers. If someone who has handled them later handles something hard like a file or plastic binder, that will transfer the chemicals, he said.
The chemicals are located at the points of the fingerprint's ridges, so what is then on the hard surface is the fingerprint in chemical. So police can not only identify the person from the print, but also connect the person and the drug or chemical, he said.
Purdue researcher Demian R. Ifa, a co-author, said the technology also can uncover fingerprints buried beneath others.
"Because the distribution of compounds found in each fingerprint can be unique, we also can use this technology to pull one fingerprint out from beneath layers of other fingerprints," Ifa said. "By looking for compounds we know to be present in a certain fingerprint, we can separate it from the others and obtain a crystal clear image of that fingerprint."
Other developments include radiocarbon dating, something most people associated with determining the age of ancient things like dinosaurs. But the atomic bomb tests in the 1950s have provided a method for more recent testing by disrupting the previously uniform levels of carbon-14 in the atmosphere.
"That introduced huge amounts of radioactive carbon into the atmosphere, and subsequently us," explained Douglas Ubelaker, a forensic anthropologist at the Smithsonian's National Museum of Natural History.
With the increase in radioactive carbon during the tests and its decline after testing was stopped, researchers were able to develop a "bomb curve" for the amount that might be found in the body of an individual.
Body cells are continually being replaced - faster in soft tissues, more slowly in bones and teeth - and comparing the ratios allows for the estimation of someone's date of death and, possibly, their date of birth, Ubelaker said.
Analyzing small particles recovered from fires and explosions can also be a challenge, according to Ubelaker, who serves as an FBI consultant.
New scanning electron spectroscopy methods have produced comparison data to determine if particles are bone or something else before researchers attempt DNA analysis, he said.
And a technique called radio immuno assay can be used to determine if a piece of bone or tooth is human, he added, solving the problem that simply looking at bone through a microscope can't always answer.
Researchers also are working to improve analysis of explosive powders based on their chemical composition, and size and shape of the powder granules used in pipe bombs, said Bill MacCrehan, who performs trace forensic chemical analysis at the National Institutes of Standards and Technology.