Using light to fight crime

After a young girl was murdered in Connecticut five years ago, the state police arrested a suspect whom they had found burning a bag of clothing. Shortly before the murder the victim had been seen carrying a bag of clothes. However, police couldn't prove that the burned bag was the girl's. They knew that her bag had contained an orange cotton and polyester T-shirt, and they found a charred piece of organic fabric in the ashes. But they couldn't identify any trace of polyester in the ashes.

At that point, the state called in John Reffner, technical director of a local firm, SensIR Technologies. "I looked at the piece of fabric with my infrared microspectroscope," Reffner recalled. "While I couldn't see any polyester, I did see some plastic residue, which turned out to come from polyester. That became very good evidence that helped to convict the suspect."

 

Infrared microscopy is one of several photonic technologies now coming to the aid of crime fighters (Figure 1.). From systems that identify the sources of spent bullets at crime scenes to sensors that detect concealed weapons, and from smart surveillance cameras to handheld devices for DNA analysis, the optics business is playing key roles in law enforcement. "A lot of what we do is based on light," said David Boyd, director of science and technology for the National Institute of Justice (NIJ), the research arm of the U.S. Justice Department.

Boyd's department aims to identify new technology that the law enforcement community needs, and then turn the technology into usable products. The fact that about 90 percent of the more than 18,000 law enforcement agencies in the U.S. have fewer than 24 officers constrains the work. Departments with relatively few police can hardly spare individuals as technical specialists. Indeed, the entire country has no more than 400 crime laboratories. So any new technology must of necessity be user friendly.

Among all the technologies under development for law enforcement, photonics probably has the most impact on forensics. "Optics plays a huge role in forensics," Boyd said. "We not only have to detect evidence invisible to the naked eye, we also have to analyze it, a process that involves optics as we're looking mostly at spectral displays."

One key area of research focuses on recording crime scenes in ways that capture information not immediately obvious to individuals on the scene. "That includes retaining spectral views of what's at the scene on the macro scale," Boyd said. "It helps to identify artifacts. It also allows us to check back in cases where the scene may no longer exist, to see if an artifact was there or not."

IR technology, meanwhile, has become an essential tool for trace analysis of crime scenes. For example, it permits identification of paint chips and enables subclassification of acrylic fibers. "You can determine the copolymers from the infrared absorption spectra," Reffner said. Forensic scientists usually work in the 2.5- to 16.5-µm range, where most molecular materials -- including plastics and paints -- have characteristic IR absorptions.

The IR microscope has particular value in criminal investigations. "You can see different shapes and forms of materials," Reffner said. "Since the resolution of the microscope equals the wavelength of the IR, you can get down to 10 µm without any need for sample preparation."

Microscopy developed by SensIR has another advantage: it can work in transmission in one of two reflection modes. The internal reflection approach gives forensic experts a particularly useful opportunity. "Since the electric field penetrates only a few microns, you can look at the surface. You can examine paint on paint, for example," Reffner said. SensIR has used this method to test defendants' claims that police officers have kicked them, by checking for shoe polish stains on the defendants' clothes.

A two-year-old case illustrates another forensic application of the IR microscope in reflection mode. A police officer in Maine was shot and wounded by a bullet that passed through his bulletproof vest and lodged in a tree, from which it was eventually recovered. The chief suspect admitted that he had done shooting in the region, but denied that he had fired at the policeman. However, examination of the bullet using IR microscopy revealed that its outer surface contained a smear of Kevlar, the material inside the bulletproof vest.

The IR microscope's ability to obtain data on the spatial distribution of compounds has found application in drug testing. Defendants in drug cases often claim that drug residues detected in their hair got there after they handled currency-which contains traces of drugs -- and then put their hands through their hair. Working with the synchrotron at Brookhaven National Lab. (Long Island, NY) Reffner's team has been able to dent that defense by locating the drug residues inside, rather than on the surface of, strands of hair.

A great deal of forensic examination takes place in police laboratories. However, it's often important to do simple procedures at crime scenes. Several organizations are working on miniature devices for instantly analyzing the DNA content of such evidence as bloodstain and semen samples at crime scenes (Figure 2).

Figure 2. (upper) Nanogen's semiconductor microchip DNA-testing lab on a chip. (lower) Nanogen's proprietary permeation layer is the interface between the surface of the microchip and the biological test environment. The permeation layer isolates the biological materials from the electrochemical environment near the electrode surface and provides the chemistry necessary for attachment of capture probes. Images courtesy Nanogen Corp. (San Diego, CA).

"We can do some rudimentary processing on a MEMS microchip that can carry out the same type of microanalysis as a crime laboratory," said Paul Matsudaira, a scientist at the Whitehead Institute for Biomedical Research, part of the Massachusetts Institute of Technology. Matsudaira's team is working on a unit consisting of small channels in a plate of silicon. Electrophoresis drives a labeled DNA sample through the channels past an argon laser that reads the samples.

NIJ takes a similar approach. "We have a DNA chip, smaller than a dime, in something the size of a credit card," Boyd said. "It's read at the crime scene by an optical system containing a laser of the size you would find in a CD-ROM player. When you put a sample in, the device converts the DNA into the same code as that used in the FBI's DNA database, so that you can try to find a match." Boyd said the next step is to develop a way to connect the field instrument to the FBI database so investigators can immediately identify artifacts at crime scenes.

Preparation of samples for DNA analysis is usually a complex procedure best done by well qualified technicians in a sterile laboratory. Crime scenes, of course, are far from sterile, and investigators are unlikely to have training in the methods of molecular biology. Thus, the technology won't be featured as evidence in court. "It will be used as an investigative tool at the scene to try to narrow the number of suspects," Boyd said.

At the same time, Boyd's team is making an effort to make crime scenes less chaotic by reducing the number of individuals who need to be present there (a problem sometimes referred to as "ego access"). In a collaboration with the New York State Crime Lab. and the National Aeronautics and Space Administration (NASA), NIJ scientists are developing "teleforensic" technology: remote viewers will transmit details of crime scenes to analysts up to several hundred miles away. "It will provide the opportunity to get expert forensic advice on how best to investigate the crime scene," Boyd said.

Law enforcement also takes advantage of optical technologies for surveillance. Watching traffic, rather than controlling it, is one objective of surveillance work. Photonics is contributing to advances in several areas.

One project under development at the NIJ involves computer modeling and the polarization of light. "By analyzing that polarization in a computer, you can take a 2D image and get enough data out of it to produce a pretty good 3D image," Boyd said. "We're looking at using it in surveillance devices, where we can analyze shadows that would normally appear black." The technology has shown its promise in tests in the laboratory and the field. "We've been successful in extracting images in much the same way that we would with infrared light," Boyd said.

To work with conventional images, the NIJ is developing smart video cameras. The team wants to reduce the need for human monitors watching out for, say, criminals leaving or entering a building that has several entrances. "It's a very people-intensive activity," Boyd said. "We'd like to have cameras that figure out when something unusual is going on, such as a truck parking for a little too long." Once a camera detects a strange occurrence, it would activate itself, zoom up to view the truck's license plate, and then focus on any individual who might get out of the vehicle and follow the person, taping the action continually.

Similar technology under development across the Atlantic has the objective of cutting the time that humans must spend watching tapes from crime scenes. Whenever a major terrorist bombing occurs in Britain, the police gather tapes of the surrounding area gathered by surveillance cameras, automated teller machines, and other devices in public areas. The process can gather up to several thousands of hours of videotape, all of which must usually be viewed by human monitors.

Now, Britain's Police Scientific Development Branch is perfecting a computer routine that can view the tapes and flag events of interest that it spots on them. The software can reduce the vast amount of videotape down to about 200 hours' worth that contains incidents possibly related to the crime. Human monitors can deal with that amount far more cheaply and efficiently than they can with the original quantity.

The technology saves police time in two ways. The cameras run continuously, but nobody has to monitor them in normal times. Then, if a crime is reported, the system highlights only the segments of videotape likely to be related to the crime for careful monitoring by human personnel.

The technology has made an appearance stateside. "Some of the British scientists have come over to work with us on developing demonstration versions of this in public areas," Boyd said. "We've had a major success with it in Baltimore."

Maintaining security is another goal of crime-fighting laboratories. Law enforcement agencies now use two systems, DrugFire and Integrated Ballistics Identification System (IBIS), to identify spent bullets and cartridge cases. In both systems, video images of striations on bullets and the markings left on cartridge cases are digitized and then compared with similar digitized images in databases. Forensic Technology, Inc., developer of IBIS, has recently introduced a multiviewer that enables an examiner to analyze multiple images of breech faces, firing pins, and ejector marks simultaneously.

The technologies have proved their value convincingly. "We've made more than 5,500 cold hits that helped the police to solve a case without any leads," said Mike Kelly, program manager for DrugFire at CSC, which created the technology. The company is now developing a similar system to identify the sources of illegally obtained prescription drugs by matching the logos or images on tablets.

Figure 3. Utilizing acoustic technology, this hand-held device will be able to detect both metallic and nonmetallic weapons concealed under an individual's clothing.

Detecting concealed weapons is another priority of NIJ. One system in advanced development is an acoustic device that applies photonic-style techniques to sound waves at frequencies too high to hear (Figure 3). "It's handheld and looks like a tin can with a gun handle on it," Boyd said. "A light helps you aim it." The instrument gained useful exposure in spring, when NIJ demonstrated it for Hillary Clinton; it immediately detected a weapon carried by one of her security agents.

Crime fighters are also applying millimeter waves to future detection of concealed weapons. Millimeter waves detect heat from the human body and other living objects. Pointed at an unarmed person, a detector of that type will reveal a complete image of the person. But a gun or other hard object between the individual and the detector will show up as a black outline. "Computer analysis of the image can increase dramatically the likelihood that it's a weapon," Boyd said. "At the very least you know there's something to check on."

Finally, Boyd and his team are working on what he calls "a poor man's MRI" for use in corrections facilities. Scientists want to automate searches of body cavities that are essential in such surroundings but demeaning to both searchers and searched. "We're developing what amounts to an MRI machine that you sit on like a saddle," Boyd said. "It will identify anything that's not part of the human body."