Future Forum: Guilt, Innocence, and the Death Penalty 
Why Can’t Steven Phillips Get a DNA Test?
In prisons all across Texas, convicted felons are asking for access to forensic evidence they insist could prove their innocence. In many cases, the requests are frivolous. But in those where legitimate questions of guilt still exist, the pursuit of justice is frequently derailed. And no one can explain why.
(Page 2 of 5)
ONE OF THE MOST PRESTIGIOUS DNA labs in the world sits in a large gray building amid dozens of modern warehouses in the North Dallas suburb of Farmers Branch. Orchid Cellmark was formed by a consolidation of four of the world’s first DNA labs. The company has worked on cases from O.J. to JonBenet and has helped identify World Trade Center victims whose remains were mere wisps of cellular matter.
On a cold December day, I visited the lab and met with Robert Giles, Orchid Cellmark’s executive director. A longtime veteran of forensic testing, Giles, 53, is a quiet and studious man. He also has plenty of patience, a virtue every DNA scientist needs, especially when dealing with people who never took classes in cellular biology or population genetics. Over the course of several interviews, he had explained—and explained again—the science of DNA testing, and we had discussed Phillips’s case.
Orchid Cellmark is no liberal defense group; though the company does pro bono work for indigent convicts seeking DNA testing, it also does a lot of work for police labs. Giles agreed to run a profile of Phillips’s DNA with the understanding that, since we were not following the standard protocols, it would not be admissible in court. Under normal circumstances, there would be a strict chain of custody (a licensed technician would obtain a sample from Phillips in the presence of a witness). But given that neither of us had legal access to the inmate, Phillips had instead simply chewed on a piece of toilet paper and sent it to me in the mail. I brought the unopened envelope with me to Orchid Cellmark. We had no way of knowing whether it had been contaminated, or even if it had really come from Phillips. But the goal of the exercise wasn’t to figure out whether the sample was really his. I wanted to understand how a DNA test works and, in the process, determine just how easy it would be to grant Phillips’s request.
After I arrived, Giles presented the envelope with the sample to analyst Jody Hrabal, who would walk me through the testing process. Hrabal, 28, has been with Orchid Cellmark for six years. One of her duties is to testify before juries, a task that has required her to come up with a concise explanation of a very complicated science. “I always make it short and simple,” she told me. “I say, ‘DNA, or deoxyribonucleic acid, is a molecule that exists in almost every cell of your body—your blood, saliva, hair, bones—that you get it from your mom and dad, and that ninety-nine percent of your DNA is the same as everyone else’s, but the one percent is what makes you unique. What we do at the lab is look at thirteen locations, or loci, on your DNA, where there are markers that repeat themselves a set number of times. Those thirteen loci combined make a unique profile for every person.’”
DNA’s markers are made up of sequences of the molecule’s four building blocks: adenine, thymine, cytosine, and guanine (abbreviated A, T, C, and G). These link with one another to form the spiraling rope ladder of DNA’s familiar double helix. There are 3 billion rungs on this microscopic ladder, and if unwrapped, the molecule would be anywhere from six to nine feet long. What forensic DNA analysts do is compare the thirteen loci of a suspect’s DNA sample—his unique profile—with the thirteen from a sample taken from a crime scene. If the number of repeating markers at all thirteen loci matches, the analyst can safely conclude that the statistical likelihood of this same DNA profile reoccurring in the general population is something like 1 in 200 billion. In other words, either detectives have found their man or something very strange has taken place, along the lines of a monkey’s hammering out a sonnet on a typewriter. (It was the FBI that chose these thirteen loci, precisely because they are so unique. Every time a DNA sample is collected at a crime scene or taken from a convict, the profile is entered into CODIS, the Combined DNA Index System, a nationwide database, which is a great crime-fighting tool, since most criminals are repeat offenders.)
Phillips’ sample was first given a number, then Hrabal and I put on lab coats, masks, and disposable latex gloves. She swabbed the inside of my cheek for a reference sample. It would be one of several control tests for contamination, which can be caused by exposure to another person’s DNA, especially in the early stages of its collection at the crime scene or in the lab. In rare instances, contamination can cause markers to show up at loci that the suspect in truth doesn’t have. DNA survives heat sterilization, so no test tubes are reused. “Everything is disposable,” said Hrabal.
Orchid Cellmark is as spare on the inside as it is on the outside, a minimally adorned maze of offices, storage areas (for the thousands of files it has worked on), and labs. We first went to a preparatory lab to remove the sample. Hrabal explained how all samples are considered either “known” or “questioned,” and since we weren’t positive where Phillips’s came from, we would call it questioned. She then opened the envelope Phillips had sent and pulled out another sealed envelope. Inside that was a small piece of carefully folded toilet paper, and inside that was the hard clump Phillips had chewed on. “Terrible toilet paper for the prisoners,” joked Hrabal. She took it into a separate room, turned off the lights, and shone a blue light on the wad; it glowed slightly, indicating saliva. “Semen glows brighter,” she said. She cut a small piece of the clump, put it in a pink tube, and we went to the extraction lab next door. There, two chemicals were added, one to break down the walls of the cells and the other to eat up all the other proteins and release Phillips’s DNA. Hrabal capped the tube and put the same chemicals in a separate tube, called the reagent blank, which would go through the whole process and be used as a check for contamination.
For the next couple of hours, the sample in the tube was shaken on a vortex machine and spun in a centrifuge, put in warm water, and dosed with ethyl alcohol and sodium acetate. At every step, Hrabal took elaborate notes, entered figures on a computer, and cleaned up instruments and work benches with bleach. “It’s kind of repetitive,” she said at one point. I told her that you probably couldn’t be much of a DNA analyst if you weren’t detail oriented. She laughed. “I don’t think you’d last very long if you weren’t.”
Finally, the sample was ready to be copied. In the early nineties, DNA testing required a quarter-size sample of blood or saliva, which was often used up in the process. Nowadays, through a process called polymerase chain reaction, or PCR, just a handful of cells taken from the skin, ear wax, or dandruff can be used—even those taken from samples degraded by the elements or partially devoured by bacteria. From these cells, a billion copies of a DNA profile can be made, allowing a sample to be tested immediately or far into the future. To get the Phillips sample ready, Hrabal added primers, which would identify the thirteen loci, and enzymes, which would do the actual copying. The tube was next placed in a thermal cycler, which would heat up and separate the strands of DNA and then cool them for the next three to four hours.
THE FOLLOWING MORNING (in the real world, a DNA test at Orchid Cellmark takes several days to run), after more shaking, stirring, and, in Hrabal’s words, “chemical manipulation,” the sample was put in an ABI Prism Genetic Analyzer, where it traveled through superthin glass capillaries, was zapped by a laser, and then photographed by a camera. The results were sent to a computer, and then, less than a day after we started the whole process, Hrabal called up a graph showing Phillips’s genetic profile.
There they were, the thirteen loci, each represented by one or two tall, thin peaks. Under the peaks were figures showing the number of markers at each locus. Though each human has the same marker at each locus—say, AGAT—there are only a certain number of repeats possible at each one. Phillips had 15 and 17 at his first, 21 and 23 at his third, and so on. I asked Hrabal if it all looked normal. “Yes,” she replied. Anything weird? “No. All the controls and the reagent blank check out.”
If this had been a valid forensic DNA test, Hrabal would have next compared Phillips’s profile with any male profile taken from the vaginal swab being stored at the lab in Dallas. Hrabal explained what she’d do. “Assuming that it was a mixture, we would first account for the victim’s profile, which we would know, and subtract it. What would be left is the male profile.” The number of repeats at each locus of the two samples would be compared, and while the odds that two males would have the same number of repeats at one locus aren’t so bad, they decrease when two locations are compared, then three, on up to thirteen. If all thirteen matched, one could reasonably conclude that Phillips is a liar as well as a rapist. If, on the other hand, just one locus was off, Phillips would be excluded, even if twelve others matched. “Your DNA is going to match your DNA,” Giles had told me, “no matter where it’s from, no matter when you took it. One group of cells from your body looks like every other.”
My Library
