Science: DNA Evidence
The FBI Crime Lab found itself on the other side of the magnifying glass in late April. A Justice Department report issued earlier in the month had pointed out slipshod practices in three of the Washington, D.C., lab’s 23 units, and there were murmurings in the legal community that hundreds of cases in which lab personnel had been involved — including high profile proceedings such as the trial of Timothy McVeigh — had been jeopardized.
A FEW HUNDRED miles away, FBI special agent Mark Wilson was also in the spotlight. Wilson is a forensic examiner in the crime lab’s DNA 2 unit, created recently to accommodate an increasing volume of DNA-related cases. He was testifying in a Nashville courtroom, where Randall Scott had been accused of sexually assaulting a nine-year-old girl.
Randall Scott on trial
Wilson’s expert testimony was crucial to the prosecution’s case. He is the best-known authority in the field of mitochondrial DNA, a new kind of DNA testing, and his crime lab unit is the only public laboratory in the country currently performing the analysis.
The Scott case was only the sixth time such evidence had entered the courtroom. DNA spoke volumes during the trial largely because it filled the vacuum left by the nine-year-old victim, who was too traumatized by her experience to speak at all.
In 1995, while walking home from the store, the Nashville girl had been violently assaulted in a muddy backyard adjacent to a boarding house on her street. She told investigators that on her way to the store she’d seen her attacker sitting on the boarding house porch. Police quickly zeroed in on Randall Scott, a boarder, and they found a clump of blood-stained, muddy clothing under his bed. Scott remained the primary suspect in spite of the fact that the girl was not able to identify him in a line-up.
DURING A MEDICAL EXAMINATION at Vanderbilt University, two body hairs had been found in the girl’s genital area. The hairs, along with the blood found on Scott’s cut-off jeans, were sent for DNA testing to Laboratory Corporation of America (Labcorp), a commercial lab in Research Triangle Park, North Carolina.
DNA testing is about probability. Labcorp found it probable, but not certain, that the blood was the victim’s. But it determined that the hairs also matched the DNA profile of the girl — not, as prosecutor Bill Reed had expected, Randall Scott.
Scott’s lawyer, public defender Mike Engle, was bound to capitalize on the ambiguous DNA results, and because prosecutor Reed’s key witness — the victim — was unable to testify in court, Reed needed stronger scientific evidence. The girl was pre-pubescent, and thus without body hair, leading Reed to believe that “this result was not compatible with reality.” If the DNA tests on both the blood and hairs pointed to Scott, Reed’s case would be airtight.
Reed needed a second opinion. He called Mark Wilson.
WHEN I VISITED the FBI Crime Lab in early June of this year, the DNA 2 unit was only a few months old. It was created specifically for mitochondrial DNA testing, a new brand, which is Wilson’s specialty.
The new approach extracts DNA not from the nucleus of a cell, but from the cell’s mitochondria, an organelle you may recall from high school biology as the sausage-shaped “powerhouse” of the cell. The mitochondria carries its own genetic code that is passed along from mother to child, unchanged, for generations. Older nuclear DNA tests work on the tissues found in a hair follicle, but only mitochondrial DNA can be extracted from the cells of the inert hair itself.
Mitochondrial DNA is proving extremely useful in forensics, because the mitochondria carries more copies of DNA than does the nucleus, giving scientists more to work with, and because it works so effectively on hairs, which are a common piece of evidence.
HAIR EVIDENCE had become key in the Randall Scott case. Nashville prosecutor Bill Reed sent the two hairs to Wilson for a mitochondrial DNA analysis. Importantly, the FBI did something with the hairs that Labcorp, as a matter of policy, had not: it washed them.
As Wilson later explained to the jury, because the hair had been found in an area where the victim had been bleeding, it was probable that her blood — and therefore her DNA — touched the hair and that Labcorp’s test had therefore picked up on genetic material that was “on the hair” rather than “in the hair.”
Sure enough, Wilson’s own analysis of the hair showed that it had “the same DNA sequence” as a blood sample taken from Scott. After five hours of deliberation, a jury convicted him of child rape and aggravated sexual battery, and he was sentenced to 35 years in prison.
The testimony given by Wilson was essential to Reed’s case. “He can distill a very sophisticated, technical, esoteric science down into something that is pretty meaningful and understandable to just about anyone who will listen,” Reed said.
TEN YEARS AFTER it was first admitted in a court of law, DNA has become widely accepted — and, as in the Scott case, embraced — by the nation’s criminal justice system. Critics tend to target laboratory procedures or the presentation of DNA testimony, but rarely is the science behind DNA assailed.
Mark Stolorow, the director of operations for Cellmark Diagnostics, a private lab, said of DNA analysis, “Investigators are using it more often. Prosecutors are being asked in court, ‘Where’s the DNA?’ In the old days, when a prosecutor would walk DNA into the courtroom, everyone’s eyes would pop out. Today, if they don’t have DNA everybody’s eyes are popping. They say, ‘What’s wrong with you? Of course you have to have DNA testing.’ “
Experts say genetic evidence is likely to become even more commonplace in the courtroom. With increasing numbers of state and local law enforcement agencies building their own DNA facilities, pushed along by $8.75 million in Justice Department grants, and with the impending arrival of a national genetic database for convicted criminals, DNA is well on its way to becoming the ultimate fingerprint.
INSIDE, THE FBI CRIME LAB looks less like a network of science sleuths than a loose assortment of high school chemistry classrooms. Connected by a seemingly intentional maze of bland hallways, the cinderblock walls are lined with earnest but peculiar bulletin board displays, such as the one decorated with pictures of a splayed victim in a jogging suit, including a close-up of a clean, white sneaker. The effect of the photographs — which may or may not be staged — is unsettling in its ambiguity: grisly murder, or instructional diagram?
But the science rises above the humble settings. Mark Wilson came to the crime lab from the FBI’s forensic science research unit in nearby Quantico, home of the FBI training academy and future location of the crime lab itself. Wilson has more swagger than one would expect from a molecular biologist, owing perhaps to his days spent as a field agent in Salt Lake City, Utah, and New York City.
“When we brought the technique back to headquarters, we didn’t anticipate the flood of cases we got,” Wilson said, noting that the waiting list for mitochondrial DNA testing is well over a hundred cases long.
Beginning with a simple glass mortar and pestle, which is used to grind up a hair in solution before DNA can be extracted, Wilson demonstrated the process for me.
DNA, A GENETIC INSTRUCTION MANUAL, is found in nearly every cell of the body and is composed of four chemicals that line up in pairs of varying patterns. Billions of these base pairs form the molecule’s familiar double helix shape.
While scientists know that more than 99 percent of each person’s DNA is identical to the DNA of every other person — coding for things such as two arms and two legs — a small amount does vary. This is where forensic scientists dust for the genetic fingerprint.
Mitochondrial DNA analysis (and one type of nuclear DNA test) uses a technique called a Polymerase Chain Reaction (PCR) to amplify the amount of DNA available for testing, a process akin to xeroxing the genetic code. Amplification is extremely sensitive, because if any foreign DNA enters the testing area — through a technician’s sneeze, say — it, too, will be replicated in the process.
“We take meticulous steps to make sure no outside contamination is introduced into this space,” Wilson said, gesturing at the smooth stainless steel tables. “Once the amplification step is set up, we leave this room and don’t ever come back.”
In nuclear DNA testing, which is employed by more than a hundred private and public labs across the country, scientists search for distinctive, repeating patterns of base pairs, and measure the length of the DNA strand for which they repeat. A repeating pattern may span 16,000 base pairs in your DNA, but only 5,000 in mine.
The mitochondria are different. There, scientists target two regions of DNA, where they determine the exact sequence of base pairs. These sequences are extremely unique.
“We don’t know exactly how rare some of these sequences are,” Wilson explains, but with a pool of more than a thousand sample sequences collected, examiners have seen few repeated patterns.
In the Randall Scott case, for example, Wilson testified that Scott’s pattern had never been seen before.
MITOCHONDRIAL DNA is a relative newcomer to the courtroom, but standard nuclear DNA and the law go back ten years. A growing number of states no longer require hearings to determine the admissibility of DNA evidence, and critics usually reserve their fire for shoddy laboratory procedures or overzealous expert testimony.
“Nobody is questioning the fundamental science underlying the technology, or the validity of the techniques when used properly,” said William Thompson, a professor at the University of California at Irvine’s criminology department. Thompson emphasized that DNA cannot definitively say whether a defendant committed a crime. This gray area can create conflict on two levels.
“One is the scientific level, where there are some interesting disputes about how one interprets tests. Then there’s the legal level, which has to do with how these disputes play out in an adversarial system,” Thompson said. “Lawyers have no stake in good science — they’re just trying to present the version that is most beneficial to their case.”
Because scientists test only a small portion of the billions of chemical base pairs that compose DNA, expert witnesses such as Mark Wilson can only speak to the probability that someone else would have a matching sequence. The DNA expert is just one piece of the puzzle, but if the odds are low — a one in a million chance, say — a jury might conclude that no one other than the defendant could have committed the crime in question. In the case of Randall Scott, the odds were against him.
UNLIKE IN THE SCOTT CASE, DNA is more effective at excluding rather than convicting a suspect, since DNA fingerprinting can only definitively demonstrate that two DNA strands do not match. Similarly, DNA is playing a huge role in cases where the previously convicted have been freed based on DNA evidence that came to light after they’d been jailed. A Justice Department report, Convicted by Juries, Exonerated by Science, documented 28 such cases; in the year since its release, 13 more have been found.
Last April, for example, a Wisconsin man named Anthony Hicks was freed after spending five years in jail for sexual assault. The evidence in the case, four hairs, was analyzed only with a microscope, and the state’s expert witness testified that they matched Hicks. But Hicks, who denied the charges, had read about DNA testing and knew to request it in his appeal.
The DNA analysis found that one hair belonged to the victim, and, while it typed the others as male hairs, they did not belong to Hicks. The state dropped the charges, and Hicks was a free man. “I’d like to say it was great lawyering, but really it was the technology,” said Steven Hurley, who handled Hicks’s appeal. “He did five years in prison and he’d still be there if it wasn’t for that DNA.”
Like the Hicks case, all 28 exonerations documented in the Justice Department report were rapes, and all the victims female. They all involved a positive identification of the convicted man by the victim, which points out the frailty of human visual memory when compared with hard DNA evidence.
WITH LAST MONTH’S DISCOVERY by Australian scientists that DNA can be extracted even from a human fingerprint, old world forensics converged with the new, at least symbolically. The news foreshadows DNA’s role in the forensics of the future, when genetic material is gathered from wider sources and used in more and more cases, ranging from the riveting to the mundane.
DNA is more than a fingerprint, of course: it’s also the blueprint for everything that breathes. As such, DNA commands attention in many walks of life. To movie makers, genetic material is the stuff that brings the dinosaurs back to life. To civil libertarians, our genes are our own business, and developments such as a national DNA database are suspect. To scientists, DNA is the chain that links us even as it individuates us, a molecule elegant in its tiny complexity.
To a crime detective, however, DNA may become the next best thing to a smoking gun.
While a clear fingerprint is, today, one of the most useful pieces of forensic evidence, it has not always been so. When fingerprints were first introduced to the United States, they received a lukewarm reception in courtrooms.
“Whenever someone brings a new technology to court, even something that seems to be reasonably common knowledge, it takes time for the legal system to accept it,” said Tom Kubic, a retired NYPD detective and currently a criminology professor at John Jay College in New York City.
Fingerprinting was introduced in the U.S. in 1904, when Scotland Yard detectives, who happened to be in St. Louis guarding the Crown Jewels at the World’s Fair, imparted the techniques to the St. Louis Police Department.
In 1911, the Illinois Supreme Court was the first appellate court to rule that fingerprints could be admitted as evidence. In the 1930s and ‘40s the fingerprint finally began to receive wide acceptance, and prosecutors no longer had to prove fingerprinting was a solid science. By 1939, legal precedent established that a fingerprint alone was enough evidence to gain a conviction.
According to Kubic, “the first real use of fingerprints for ID was in India, to prevent retired soldiers from collecting triple and quadruple pensions from the army.” A British administrator in India, named William James Herschel, began studying the uniqueness of fingerprints in the late 1850s, and by 1858 he had determined each person had different prints.
A Paris police clerk, Alphonse Bertillion, is credited with popularizing fingerprints in the late 1890s. He had developed several systems of identification, the most popular being using the measurements of several body parts. While that system eventually proved flawed, it initially was favored over fingerprinting. But in 1902, Bertillion was the first to successfully identify a suspect solely by fingerprints.
Long before they were accepted in a court of law, fingerprints were used for varying purposes throughout history.
The earliest surviving fingerprint is a small, clay seal on a Chinese bill of sale dating from the third century, B.C., and evidence suggests Babylonians also used fingerprints to seal contracts long before that. However, scholars say these fingerprints weren’t for identification, but instead were used because it was believed a touch of the hand made the deal sacrosanct.
If there was any doubt that the badge-flashing, just-the-facts G man is a relic of a bygone era, CODIS, the FBI’s expansive new DNA-databasing effort should put it to rest.
A national framework for storing, tracking, and searching DNA-specimen information, the Combined DNA Index System, or CODIS, presages an era where biochemistry, forensics and database technology are the FBI’s most promising weapons against crime.
In a recent speech, FBI director Louis Freeh stated that “today when new FBI agents graduate from our training academy in Virginia, they leave with their firearms and their badges, but they also leave with a laptop computer. It’s an excellent symbol of the changing environment in which these young men and women will function over the next 20 years.”
In fact, CODIS is only one of a number of new FBI crime fighting initiatives that have information technology at their core. There is the CITAC computer investigations program, “DrugFire,” which creates and stores digitized images of casings found at crime scenes, and a plan to transfer 30 million fingerprints into electronic format.
Begun as a pilot program in 1990, the CODIS project didn’t receive its full charter and funding until the 1994 crime bill. It now coordinates 45 states’ efforts to catalog the DNA of potential suspects and victims. But as in other areas where technology and law enforcement meet, CODIS has sparked a heated debate over issues of privacy and confidentiality.
In 1991, James Watson, the DNA decoding scientist who with Francis Crick won the 1962 Nobel prize, told a congressional committee, “The idea that there will be a huge databank of genetic information on millions of people is repulsive.” Yet the CODIS database is hurtling toward just that. Ninety percent of the American population live in states with legislation compelling convicted offenders to provide biological samples.
But convicted criminals aren’t the only ones whose DNA is kept on computer file. Armed Forces recruits, Pentagon employees, and newborn babies, whose blood is taken as part of mandatory state screening programs for hereditary diseases, are also DNA donors. (The infants’ DNA information, stored as dried blood spots on paper “Guthrie Cards,” is kept for anywhere from a few weeks to 25 years.) By the year 2000, there will be over 4 million DNA samples in government databanks.
The controversy came to a head in 1996 when two marines were court-martialed for refusing to donate blood samples. The move provoked criticism from civil libertarians and medical ethicists, who considered the policy a clear violation of privacy rights. Others pointed out the “extreme” potential for abuse. University of Hawaii professor Kenneth Kipnis noted, “It’s impossible to imagine how these samples will be used in 75 years.”
Genetic information would be extremely valuable to a slew of private and criminal interests: medical insurers, biotechnology firms, fertility companies and computer hackers. Critics warn that without adequate controls, the databases could easily be misused to arrest “suspects” or make public an individual’s medical history.
In May of this year, 44 states received Justice Department funds to improve their DNA-analysis capabilities. Furthermore, all five states that do not currently allow DNA evidence in criminal trials are seeking to make it admissible. CODIS is expected to fully integrate state and local databases and go “online” within six months.
As anticipation of that day grows, so too does concern over the possibility of privacy rights violations and database security breaches. While CODIS offers promising new ways to fight crime, in the wrong hands it could be an equally effective tool in creating it.