Imagine, for a moment, that you are impaneled on a jury, listening to detailed, complicated DNA evidence implicating the defendant in a rape--or a murder. Blown-up charts and graphs rest on easels in front of you. A scientist is pointing at different areas on the placards. The expert is telling you that these little blips and squiggles show a likely match between the defendant's DNA and that found in samples at the crime scene, or on the murder weapon. What do you make of the explanations? What these blips and squiggles mean, you are told, is that there is only the slimmest chance that another person, randomly selected, would also have DNA that matched.
If you're like many jurors, you might be convinced of the defendant's guilt. Faced with the evidence--dense, difficult to understand, specific, and scientific--jurors are often immediately persuaded by DNA tests.
"Jurors attach a great deal of significance to this evidence. That's one of the reasons we have to be so careful about it," explains attorney Joe Margulies. "Jurors hear 'DNA' and think, 'That's it. He's guilty.'"
For those of us who are not scientists, we hear about DNA evidence and we assume it's rock solid. We've heard the stories of death-row inmates who were cleared at the 11th hour, thanks to new DNA evidence. We've heard the stories of old, unsolved cases where the culprits were finally discovered and convicted, thanks to new DNA evidence. We take for granted its veracity. If a scientist tells us the DNA matches, who are we to argue?
For precisely those reasons, Margulies contends, DNA evidence must be tested, retested, and independently proved reliable. That contention is at the heart of two appeals currently being considered by the Minnesota Supreme Court. Until then, the state's forensic experts at the Bureau of Criminal Apprehension are using a DNA test that in the end might or might not constitute adequate evidence to convict someone in a Minnesota court.
The most dramatic potential outcome is that the test would be found inadequate--and as a result, suspects can't be convicted and criminals already imprisoned must be retried. But even if the tempest ends up being a legal technicality (a far more likely scenario), it means a growing backlog of trials as prosecutors wait to proceed until they know whether DNA evidence can be introduced. Just last month in Hennepin County, for example, a judge ruled, reluctantly, that the DNA test used by state forensic scientists would not be admitted into evidence in eight pending trials.
The bottom line? Until the justices decide whether they agree with the arguments of Margulies and the other attorneys involved in the appeals, any criminal case that relies on DNA evidence, anywhere in the state, could be delayed.
To Minnesota's Bureau of Criminal Apprehension (BCA), the "polymerase chain reaction-short tandem repeat" (PCR-STR) test looked like a significant advance in methods for processing DNA when it arrived on the scene in the late 1990s. The BCA had been using DNA tests to gather evidence since 1991, but this new test promised to be both more informative and more efficient.
Using a new technology, the test required only a tiny amount of evidence, replicating a billion copies of the genes in question so that investigators could more easily create a profile of the underlying DNA. With a sample (a bloodstain, saliva from a cigarette butt, a single hair) just one-twentieth the size of that needed for previous tests, the PCR-STR test could offer proof that astoundingly few randomly selected people would likely have DNA matching any given sample. Just one in a quadrillion, in fact. While that doesn't necessarily implicate a particular suspect, it does serve to narrow the field of possibilities. "We get so much information out of a very, very small sample," explains James Iverson, the BCA's forensic science supervisor.
The prospect was exciting, for the BCA investigators and for prosecutors. Every scientific advance potentially increases the amount of information that can be determined from crime-scene evidence. More detailed scientific data could only bolster investigations and get closer to the truth about what transpired. Even long-dormant "cold cases" might finally be laid to rest, aided by new evidence made available by the test.
As the BCA set out to implement the new DNA test, Iverson says, it looked at two companies that provided kits to do the testing, Applied Biosystems (also known as PerkinElmer) and Promega. The BCA selected Applied Biosystems. "At the time, Applied Biosystems was farther along with the setup and instruments," Iverson explains. The BCA, he continues, did at least a year's worth of testing in order to prove that the kits worked and gave consistent results, and in 1999 the agency launched the new method of gathering DNA evidence. "Once you start going down one road," Iverson adds, "it's hard to go backwards."
Today, Iverson says, some 200 labs across the nation use PCR-STR testing, and 85 percent of them use the Applied Biosystems kits. According to Hennepin County prosecutors, the test has been challenged in courts nationwide, with appellate courts in 26 states deciding to admit the evidence. To the BCA and prosecutors, the test's reliability is a foregone conclusion. "I have zero concern," says Senior Assistant Hennepin County Attorney Steve Redding, a prosecutor who has used evidence from the new procedure in criminal trials.