May 09, 2003 

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DNA Detective
January 25, 2001
Christopher Ochoa - Innocent
Christopher Ochoa is found innocent.

When the results of DNA tests recently freed Christopher Ochoa after he spent 12 years in a Texas prison, he became the latest of almost a hundred prisoners whom genetic evidence cleared of serious crime charges, not to mention the hundreds of suspects who have been exonerated.

As the technology continues to advance, forensic scientists and legal experts alike are turning to this powerful biological tool more than ever before.

Genetic blueprints

Ochoa had an emotional reunion with his mother after his long stay in prison, but Frank Lee Smith wasn’t as fortunate. Smith died of cancer in prison early last year after spending 14 years on death row for the rape and murder of a little girl. Last month, however, DNA tests showed he didn’t commit the crime.

Although the testing was done too late to save Smith, the forensic scientists who perform DNA tests say their work can be gratifying. "One of the more satisfying things we do is to prove that someone who’s been suspected or even arrested of a crime has not actually committed that crime," says Robert Shaler, director of the New York City Forensic Biology Laboratory.

DNA Fingerprinting
The identical DNA bands seen in the three lanes on the right are from one person while the bands in the three lanes on the left are from a second individual.

It used to be that forensic experts had to rely on fingerprints to place suspects at crime scenes. DNA is like a fingerprint, in that everyone’s is unique, but it’s also much more precise. "Fingerprints are found at crime scenes all over the country but a vast majority of them are unusable, whereas a single molecule of DNA potentially can be used to identify an individual," says Shaler.

A genetic blueprint of who we are, DNA can be isolated from a variety of materials, including blood, bone, saliva, semen, and hair. Experts begin by isolating the DNA from samples found at the crime scene and determining how much of it there is.

They then copy it many times using a technique known as the polymerase chain reaction (PCR). At this point they use a DNA sequencer to separate the DNA into graphs or bands that are unique to every individual. The patterns of these bands can then be compared to the DNA patterns of the suspect to see if there is a match. "We are looking at specific regions of the DNA that show differences among people, and by looking at 13 different regions, or 19 different regions in the case of my laboratory, we are able to make very, very specific identifications of individuals," explains Shaler.

Life changing results

Robert Shaler and technician
Robert Shaler and his lab technician work with DNA samples.

DNA testing can be applied in a variety of ways. "One is to take a crime scene sample and compare it to another crime scene sample and show that that particular crime was committed by the same person," says Shaler. His laboratory has also matched samples with the DNA of arrested suspects who are on trial, as well as those already incarcerated.

But those with the most to gain from DNA testing are the more than 3,000 people on death row. Smith would have been the tenth person facing the death penalty to be exonerated based on DNA evidence, which has only been used since the early 90’s.

Opponents of the death penalty question why the test isn’t used more often. "The cost of having the death penalty is absolutely enormous and the cost of the DNA test is not particularly high, and falling," says Eric Freedman, a law professor at Hofstra University Law School. "And of course, if somebody is released, then the state has no cost whatsoever."

During the presidential campaign, George W. Bush said he supported DNA testing if it can confirm guilt or innocence in a death penalty case. But New York and Illinois are the only two states where death row inmates have a right to DNA testing.

Freedman points out that DNA testing is not a panacea. "It is an ability to get a window on the accuracy of the criminal justice system in a small category of cases where biological evidence exists," he says. But to those accused or convicted of crimes, this scientific tool could make or break their cases. For some, it could even prove to be a matter of life or death.

Elsewhere on the Web

Techniques for DNA Testing

Death Penalty Information Center

DNA Fingerprinting

The Innocence Project at Cardozo School of Law

National Commission of the Future of DNA Evidence

The Constitution Project’s Death Penalty Initiative



by Jill Max


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