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Making The Crime Scene Blink: NIJ Asks Sandia To Develop Portable Evidence Finder

October 22, 1997
Sandia National Laboratories
An evidence detection system that makes organic substances appear to blink, allows investigators to locate potential evidence like fingerprints, semen and urine more quickly and in a lighted room if necessary.

ALBUQUERQUE, N.M. -- Some evidence is hard to find, particularly the kinds ofevidence that can help police place the perpetrator at the scene of the crime --fingerprints, semen, urine, and other organic substances that carry clues to acriminal's identity.

Now researchers at Sandia National Laboratories are developing anevidence-detection system that would -- with the aid of a flashing lamp and apair of modified 3-D video game goggles -- make organic substances appear toblink, allowing investigators to locate potential evidence more quickly and in alighted room if necessary. The National Institute of Justice, the research armof the Department of Justice, has provided $393,000 for the project.

The researchers hope to begin testing a prototype of the system in 12 months andhave it available for licensing and manufacture in 18 months. The AlbuquerquePolice Department's crime lab has agreed to test a prototype system at actualcrime scenes.

"If it works, this system would give us the ability to see things we haven'tbeen able to see more quickly and in ambient light," says APD CriminalisticsDirector Ann Talbot.

An important feature of the system is its affordability, says Dave Sandison,lead researcher for the project. "We don't want to develop something the FBIwould have two of and nobody else could afford," he says. "It would beaccessible to police departments everywhere."

The approach originates from a Department of Energy-sponsored weapons securityproject.

Less thinking when it's blinking

To locate certain organic evidence, fingerprints for example, police typicallyrely on optical aids such as powders, lamps giving off various wavelengths oflight, and yellow-tinted goggles that increase the evidence's visibility. Evenwith these aids, investigators typically must conduct their investigations atnight or in a darkened room. It can take hours to scour every inch of a crimescene.

Most fingerprints that are discovered are lifted from smooth surfaces such asglass windows or polished furniture, says Talbot. Latent fingerprints on wallsand other textured surfaces are more difficult to find, and some kinds oforganic evidence, such as semen or urine, don't show themselves even withoptical aids.

Sometimes fluorescent dyes are used in situations where they won't contaminateother evidence, but rarely and as a last resort. "If you use chemicals, youtypically have to spray down the entire room," Talbot says. "That can getexpensive."

A lot of potential evidence can go unnoticed, she says.

Sandia's proposed evidence-detection technique relies on the fact that all typesof organic substances give off weak fluorescent emissions, normally invisible tothe naked eye because other, much brighter sources of light interfere. Theproposed system takes advantage of the periodic dissonance between two signalsat slightly different frequencies -- an effect called heterodyning -- as well asthe human eye's natural affinity to anything that moves or blinks."We like to say, "There's less thinking when it's blinking," " says Sandison.

On, off, on, off, on, off

In a nutshell, the system's lamp is modulated at a specific frequency, say 100times per second, which is to say it flashes at a rate too fast for the humaneye to detect. The glasses, modified from a 3-D video game, shutter open andclosed at a slightly different frequency, say 102 times per second, whichessentially turns the user's eyes on and off at a rate also too fast to bedetected by the human eye. To the wearer, the lenses appear transparent.Every so often, about twice a second, the glasses shutter open at the exactmoment the lamp is "on," which for a split second drowns out most backgroundlight whose wavelengths are different than that of the lamp. With the backgroundlight masked, the net effect is that the fluorescing materials appear to flashbrightly at a rate that is distinctly noticeable to the human eye.

From behind the shuttered glasses, the crime-scene investigator would see theroom lighted normally, but any organic substances would flash a few times persecond when illuminated by the system's lamp.

It's like the combined sound two jetliner engines make, every once in a whilehumming in harmony and alternatingly reverberating in discord. The engines humwhen the acoustic wavelengths match up. They clash when they don't.The researchers may also test the system using a low-light video camcorder thatis more sensitive to the fluorescence than the human eye.

Law enforcement practicality

The APD crime lab tests are intended to help work out any bugs in the technique,define what kinds of evidence it can help find, and determine whether the systemwill be practical as a law enforcement tool.

"Who knows, we may turn the system on and see thousands of fingerprints," Talbotsays. "If we see too much, we won't be able to sort out the real evidence."But if it works with some discretion and it's portable, it would be useful tous on a fairly frequent basis. The beauty of this approach is that it doesn'tcontaminate other evidence."

It may be particularly useful at sexual assault crime scenes for identifyingsemen, which fluoresces much more brightly than the oils from fingertips. Theresearchers also hope to determine whether fresh fingerprints fluoresce morebrightly than organic substances that have been there for awhile. If so, thesystem might be good at screening out evidence that isn?t pertinent to aninvestigation.

A related system is being used by a private company for detecting cancerouslesions in tissue samples. And Molecular Technologies Inc. (run by Ned Godshall,a Sandia researcher on entrepreneurial leave-of-absence) has appliedfluorescence to the problem of DNA sequencing. The heterodyning techniqueoriginates from an early 1990s Sandia weapons security project.

Sandia is a multiprogram Department of Energy laboratory operated by LockheedMartin Corp. With main facilities in Albuquerque and Livermore, Calif., Sandiahas research and development programs contributing to national security, energyand environmental technologies, and economic competitiveness.

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Sandia National Laboratories. "Making The Crime Scene Blink: NIJ Asks Sandia To Develop Portable Evidence Finder." ScienceDaily. ScienceDaily, 22 October 1997. <>.
Sandia National Laboratories. (1997, October 22). Making The Crime Scene Blink: NIJ Asks Sandia To Develop Portable Evidence Finder. ScienceDaily. Retrieved May 22, 2017 from
Sandia National Laboratories. "Making The Crime Scene Blink: NIJ Asks Sandia To Develop Portable Evidence Finder." ScienceDaily. (accessed May 22, 2017).