How Science Solves Crimes

To the untrained eye, the misshapen lump of lead looks utterly worthless. But to the examiners in the windowless lab of the Bureau of Alcohol, Tobacco and Firearms in Rockville, Md., this is pure gold: a fragment of the slug that could link the latest victim of the sniper rampage to the ones who came before. Like the other bullets, this one is carefully carried into the lab and hand-delivered to Walter Dandridge, 50, the principal examiner in the case. Using a bit of sticky wax, he attaches the crumpled slug to a slender rod suspended under his Leica comparison microscope, positioning it side-by-side with one of the bullets fired by the sniper. Then he rotates the slugs 360°, turning them back and forth like paired dancers beneath his eyepiece. After a long study, he pushes away from the table. It will take several hours for section chief Timothy J. Curtis, 46, to formally confirm the findings, but the outcome seems clear. The bullets match. The Beltway killer has struck again.

If there’s any consolation for horrified Americans watching the drama of the sniper slayings unfold, it’s that now, more than ever in history, officials have the skills to catch so slippery a killer. Even as the shooter–or shooters–taunted investigators by picking off more victims last week, authorities unleashed an unprecedented arsenal of tools to crack the case: geographic-profiling computers to try to pinpoint the killer’s home, ballistics databases intended to link his unique bullet markings to other crimes and trace-substance technology to lift whatever clues (fingerprints, DNA) might adhere to a shell casing or a tarot card.

Even with all this data in hand, good luck or a good tip may still be necessary to nab the suspect. But investigators are less dependent than ever on chance, and what they have unveiled this week is only a sampling of what they have in their high-tech kits. There are computer programs that turn muddy surveillance videos into crisp digital images. There are chemical scanners that probe evidence, one molecule at a time. There are experimental–and controversial–sensors that analyze a suspect’s brain waves and determine what he knows and what he doesn’t. The business of tracking down and picking up crooks is undergoing a technological revolution. The public, always hungry for the Next Big Thing, has not failed to notice–and neither has the entertainment industry.

TV viewers can tune into a forensics drama almost every night of the week, starting with the trendsetting CSI on CBS; its first-season spawn, CSI: Miami, also on CBS; and Crossing Jordan on NBC. On cable, The Forensics Files is Court TV’s biggest prime-time show ever, while Autopsy is wooing–and spooking–viewers on HBO. “The combination of science and police work really drives a drama,” says Tim Kring, executive producer of Crossing Jordan.

But drives it where? There are plenty of experts who wonder if turning criminal science into a craze is a good thing. Solving crimes is not nearly so quick and reliable a job as a 46-min. story line would make it seem. Investigations can take months, evidence can get muddled and courts, dubious about all the new gadgetry, are often reluctant to trust it. And that doesn’t touch the swamp of constitutional questions raised when a prosecutor tries to wade into a suspect’s brain and DNA. “TV has romanticized forensic science,” says Susan Narveson, head of the forensics lab of the Phoenix, Ariz., police department and president of the American Society of Crime Lab Directors. All this creates unrealistic expectations in the minds of the public and juries.

Part of the problem is that forensics has always been equal parts art and science, a point made in January when a Philadelphia judge threw out fingerprint evidence in a murder case after an expert could not explain to his satisfaction why such identifications are considered reliable. The judge later reversed himself, but, says assistant federal defender Robert Epstein, who brought a challenge to the admission of fingerprint evidence in a robbery case, “even if the judges are going to let [fingerprint evidence] in, it doesn’t mean juries are going to accept it uncritically anymore.”

At its best, then, forensics is an uncertain business, the onion-peeling exercise of investigating a crime using everything from shoe-leather detective work to the forensic accounting applied to Enron-type cases. Crimes of passion or violence, however, require a whole different set of tools, and it’s here that much of the new science is found.

Ever since the evidentiary orgy of the O.J. Simpson trial, forensics for many people has been associated with one thing: DNA. And with good reason. The ability to extract cells from body fluids or tissue and use them to identify a person with near certainty has shaken up criminalistics like nothing before. As technicians have got better at extracting DNA from ever smaller samples, the technology has become increasingly useful, allowing evidence-rich cells to be drawn from traces of sweat, tears, saliva and blood spots a tenth of an inch across. Says Barry Fischer, director of the Los Angeles sheriff department’s forensics lab: “You can get good DNA from a hatband or the nosepiece of a pair of glasses.”

What’s surprising even scientists is the other–even less likely–places they can get it. DNA is generally found only in cells that have a nucleus, which rules out cells in fingernails, teeth and the shafts of hair. What those cells do have, however, is something called mitochondrial DNA, a more primitive form of genetic coding inherited from the mother only. A mitochondrial-DNA sequencing technique developed by anthropologists to help trace human ancestors has been adopted by pioneering crime fighters. Nobody pretends that the new technology is anywhere near as precise as traditional DNA profiling. Nonetheless, later this month an Iowa man, Stephan Zanter, 46, may come to trial for a murder committed in 1989, thanks to mitochondrial testing of two hairs found at the scene.

But for all its glamour and promise, DNA testing is not the technology that truly excites forensic scientists–or the people who make TV dramas. What thrills them most is the hardware–the scopes and scanners and mass spectrometers that allow investigators to peer with remarkable precision into any given piece of evidence.

For example, one of the jobs criminal investigators routinely perform is testing for gunpowder on suspects’ hands. In the past, this was a surprisingly low-tech chore, involving melting a glob of paraffin in a pot and painting it onto the fingers and hands. The wax was then peeled off and treated with chemicals that react to gunpowder traces. If the chemicals turned up positive, you had your shooter–unless, of course, the chemicals were reacting with urine, bleach or fertilizer, which had a nasty habit of yielding identical results.

Today most forensics labs that conduct the test rely instead on scanning electron microscopes. Just touch a bit of tape to a suspect’s hands, place it under the scope and hit it with a stream of electrons. The elements in gunpowder give off distinct X-ray signatures, and if they are there, the electron beam will spot them. The drawback? “You don’t get to see the terror on people’s faces when you pour hot paraffin on their hands,” says Fischer. “I think it encouraged some people to confess.”

Equally impressive are the new gas chromatography and mass spectrometry machines. To test a bit of evidence whose chemical composition is unknown, investigators place it in a gas chromatograph–essentially a high-intensity oven–where it’s vaporized. The resulting gas is funneled into a coil-shaped structure lined with chemicals that cause the components in the gas to exit at different rates. These components are then sorted by atomic weight and converted into a graph. Investigators then compare the readout with a reference library, determining what the evidence is made of.

The problem with gas chromatography and mass spectrometry, however, is that in order to analyze evidence, you have to destroy it–which means investigators have to get the test right the first time, or the perp might walk. A new laser ablation spectrometer under development could solve that problem by etching off only a tiny slice of a sample with a needlelike light beam and cooking it in a plasma furnace equipped with a mass spectrometer especially sensitive to trace elements. Similarly, researchers at California’s Lawrence Livermore National Laboratory have shown that a synchrotron radiation device can bounce a beam of infrared energy off a piece of evidence and analyze the spectrum of its reflection without damaging the sample. Researchers are also trying to use infrared hardware to analyze the composition of the oils in fingerprints, which would allow suspects to be identified not just by their print patterns, but by their chemistry as well.

Sometimes the best prints don’t exist in the real world at all. In some forensics labs investigators can take digital snapshots of a fingerprint on, say, a colorful soda can, then manipulate the image to float the print off the can. “We cancel out the background,” says Narveson, “which gives us a lot better chance to capture the detail of the print.”

Perhaps the most futuristic of the new crime-busting technologies, and one that is also the subject of disputes, is a procedure known as brain fingerprinting (see box). The principle behind the technique is that when the brain processes an image it recognizes (as opposed to one it has never seen before), it emits distinct electrical impulses that are detectable by scalp sensors. A positive response to a photo of a crime scene may mean a suspect was there before; a negative response may help confirm an alibi.

Other technologies are less experimental. One of the fondest dreams of law-enforcement officials is to build a national computer system that holds the fingerprints and DNA of every known felon and the ballistic signature of every gun ever used in a crime. Early versions of each of these databases–the Combined DNA Index System (CODIS), the National Integrated Ballistics Information Network (NIBIN) and the Integrated Automated Fingerprint Identification System (IAFIS)–already exist, but they are not yet all fully operational.

The ballistics network has been slow getting implemented nationwide. But when it works, it works well. Kareem Willis, 20, was arrested last year in New York City for armed robbery. When police tested his gun, they were able to link it to four shootings and three deaths. He’s now serving 25 years to life for two of those killings. “We have evidence sitting in here linked to numerous other crimes,” says Detective Mike Boncimino. “Eventually they’re going to get caught with the gun.”

The DNA database is also nowhere near complete, in part because of the legal complexities of obtaining DNA samples. In California a program that required felons to submit DNA samples was challenged by a group of female inmates on death row who claimed it would violate their privacy. They and several hundred other inmates refused to give up their DNA. The state supreme court slapped down the suit by refusing to review the matter, and last month Governor Gray Davis signed legislation allowing jail officials to take samples by force if necessary. “I logically cannot see the difference between a person’s fingerprint and a DNA fingerprint,” says Lisa Kahn, a Los Angeles prosecutor. Argues Peter Neufeld, co-founder of the Innocence Project: “Fingerprints don’t tell you anything other than a fingerprint.” With DNA, “there is potentially a lot more information about people that we may not want to share with the government. How would you feel about it if your complete DNA profile was kept in Washington with the Department of Health?”

The irony is that DNA evidence can also clear a condemned prisoner. Earlier this month Montana inmate Jimmy Ray Bromgard, who had already spent 15 years in jail, became the 111th person in the U.S. exonerated by postconviction DNA testing aided by the Innocence Project after it was revealed that semen found on the victim’s clothing was not, in fact, his.

For folks who get their forensics strictly from the prime-time dramas, things are a lot simpler–and prettier. Watch an episode of CSI, and you would think forensic investigators move in a world of lab coats fresh from the cleaners, offices done up in glass brick and autopsy tables artfully–and pointlessly–underlit in purple. The fact is that in communities in which forensic labs compete for funds from the same pot of money out of which beat cops are paid, there’s no room for such luxuries. Even gadgets like the mass spectrometers get snazzed up for TV, with flashing lights and screen images that simply don’t exist. “We like high-tech gadgetry,” says Crossing Jordan’s Kring. “And there are a lot of gadgets that spin, light up and make funny noises.” That doesn’t always go down well with real scientists. “I don’t think you’ll find too many criminalists who watch these shows,” says criminalist Lynne Herold of the L.A. sheriff’s lab.

Then there’s the problem of time. As Americans have learned by watching investigations from Ted Bundy to Son of Sam, most criminal cases don’t get cracked overnight. On TV, however, investigators have less than an hour to go from crime to capture, so time lines get dramatically–sometimes preposterously–compressed. “People expect DNA to go into a box and results to come out two hours later,” says Fred Tulleners, a lab director with the California Department of Justice. “The reality might be two months.”

The myth of quick-and-easy crime busting may be starting to get in the way of law enforcement. Forensic scientists speak of something they call the CSI effect, a growing public expectation that police labs can do everything TV labs can. This, they worry, may poison jury pools, which could lose the ability to appreciate the shades of gray that color real criminal cases. That, in turn, could discourage prosecutors, who may be reluctant to pursue good circumstantial cases without a smoking gun. “Attorneys may not be willing to go to trial unless you have statistics of one in a million,” says criminalist Faye Springer of the D.A.’s forensic lab in Sacramento.

Even rookie criminalists are beginning to rely on snazzy science first and street smarts second. Fischer reports that when he is interviewing job applicants for the L.A. sheriff’s lab, one question he asks is what they would do if they came upon a murder victim clutching a plastic bag containing a blue powder. Typically, the applicants tick off the string of high-tech tests they would conduct on the substance. What they never ask is where the body was found. “If it was in a Laundromat, he probably had detergent in the bag,” says Fischer.

Knowing when to use and not use the new forensic tools is an instinct best bred in the labs themselves, but the quality of those facilities varies widely. There is no national standard for training required to become a forensic investigator, nor any uniform accreditation procedure for labs. About two-thirds of U.S. forensic labs subscribe to an accreditation system, but it’s only voluntary. “When you get a haircut,” says Fischer, “even your barber is licensed.”

The risks of such casual oversight–coupled with the pressure that labs are under to produce evidence–were underscored last year when Oklahoma police chemist Joyce Gilchrist was fired, allegedly for committing scientific errors and misinterpreting results. The state is reviewing more than 1,000 cases she handled. Gilchrist denies any wrongdoing.

Clearly scientists need to be better trained, and on this score things are improving. The L.A. sheriff’s office runs forensics courses for detectives that include fake murder scenes staged at a Residence Inn. The University of Tennessee in Knoxville maintains a politely named Anthropological Research Facility, a body farm where dozens of human remains lie in various states of decay in open fields to help forensic scientists better understand decomposition.

While such work can be grisly, there’s no shortage of new recruits anxious to enter the field–thanks in part to the CSI-type shows. Since the programs went on the air, the American Academy of Forensic Scientists has been flooded with e-mail from viewers hoping to enter the field. In 1993 Michigan State University received 60 applications for 12 spots in its criminal-justice program; this year the number rose to 147. At West Virginia University, 200 students were enrolled in the school’s forensic-science program in 1999; this year that figure doubled. The University of California, Davis, which already offered an undergraduate forensic degree, has taken the training a step higher, establishing a master’s program too. Interestingly, most of the applicants at many of these programs are women: 70% at West Virginia University; 80% at Michigan State. Jay Siegel, a director of Michigan’s school of criminal justice, speculates that female students are drawn to forensics because gender bias still limits women’s opportunities in other sciences. Polls also suggest that women more than men identify crime as one of society’s most pressing concerns.

The more TV dramas draw viewers into the field, the more universities are likely to strengthen their curricula. That, in turn, could help the investigative arts harden, at last, into the true science they need to be. This won’t please criminals, but it might also disappoint the new crop of forensic scientists. Raised in a world of CSI bells and Crossing Jordan whistles, they may not be prepared for the fact that forensics is not always fast or fun or pretty. It’s a grueling business of trial and error, of investigative dead ends, of repeating the same experiment over weeks or months, until finally, one day, all the tumblers click into place and the bad guy is at last yours. It isn’t prime time–but it’s not a bad day’s work either. –Reported by Dan Cray and Jeanne McDowell/Los Angeles, Amanda Bower, Sora Song and Deirdre van Dyk/New York, Sarah Sturmon Dale/Minneapolis, Elizabeth Kauffman/Nashville and Elaine Shannon/Washington