DNA Frees Death-Row Inmates, Brings Others to Justice

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Such post-trial exonerations are likely to become a thing of the past, because modern, accurate, affordable DNA testing has become a common pretrial practice.

"We have an increasing number of between 2,500-3,000 DNA cases each year," Mange said. "Juries are coming to expect it, especially because they are being trained by TV. But there is a disconnect between CSI and the things that we can do, and that's a concern. We can't get returns on DNA cases in an hour."

DNA evidence is also subject to human error. Confidence in many testing labs has been shaken by confirmed cases of botched, falsified, and otherwise erroneous procedures, most infamously at the Houston Police Department crime laboratory, where a 17-year-old boy was convicted for rape based on improperly processed DNA samples.

While exonerations of death-row inmates and violent criminals are usually subject to very stringent testing control, such has not always been the case with pre-trial DNA evidence.

"Just because you're doing DNA testing, people shouldn't always consider the results 100 percent reliable," Dieter explained. "Much depends on the quality of people collecting the evidence, doing the testing, doing the probability calculations—all of this is subject to human error."

Reform Needed?

Rob Warden, director of the Center on Wrongful Conviction at the Northwestern University School of Law in Chicago, said the United States' many labs and controlling agencies are in need of fundamental reform.

"The most fundamental reform would be to establish reliable scientific procedures in crime labs," he said. "They should be independent of law-enforcement agencies. Scientists should not know what the desired outcome of the test is. Instead, it sometimes happens [that officials say,] 'Here's a semen sample from the victim, and here's the suspect's sample—can you match them?' That shouldn't be the question."

Even when DNA evidence is accurately managed, using it to prove innocence or guilt is not always straightforward.

"People confuse the presence of biological material and DNA with its ultimate use," said John Bradley, the district attorney of Williamson County, Texas.

"DNA means that a biological material is present, but there is still a lot of work to be done to draw truthful inferences from it, from the prosecutors' or defendants' viewpoint. You can go into any room anywhere and likely find some DNA, but it doesn't resolve the question of what does that DNA mean?"

Bradley explained that not only are juries becoming more DNA savvy but defendants are as well.

"In a few interesting cases defendants have come close to manipulating DNA in ways that led the case away from themselves," he explained.

A Saskatchewan, Canada, doctor was accused of raping a sedated patient 1992 but readily consented to DNA blood tests, which indicated that he was not the rapist. Only after the victim hired a private detective did the truth emerge.

The physician had twice implanted into his arm plastic tubes of another person's blood. He was eventually convicted in 1999 and served about four years in prison.

"It really opened my eyes," Bradley said. "As much as we can make mistakes as prosecutors, we have to be aware that defendants can also manipulate the system."

Bradley cites other complex examples of intentional DNA manipulation. For instance, a serial rapist paid prostitutes for semen-filled condoms and used the fluid to confound DNA testing. Also, several Texas prisoners switched identity armbands prior to blood sampling, fooling a nurse who did not know the inmates.

Despite the challenges, DNA is helping law enforcement to close the books on many cases that had been unresolved for years.

The United States' Combined DNA Index System (CODIS) compares DNA profiles of convicted sex offenders and other violent criminals with evidence from unsolved cases.

"We had a serial rapist who raped two little girls, and the detectives had decided that there was no way to solve the case," Mange, the Texas Department of Public Safety spokesperson, said. "But five years later we submitted the evidence [to CODIS], and we got a match. We never would have solved this case in a million years without CODIS, and these girls were living in fear, because they thought that this person was out there."

The booming use of DNA testing has led to enormous backlogs in many labs, and lack of public funding for the tests has frustrated prosecutors and defenders alike.

With DNA's importance likely to grow, both groups hope that increased funding will help the wheels of justice turn fairly and quickly.

Sound off with your thoughts on the U.S. prison system in the Explorer blog.

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