Deoxyribonucleic acid (DNA) is a material component of chromosomes that programs how human beings develop, grow, and function. All humans are thought to have DNA that is 99.9% identical, but the remaining 0.1% marks each of us as unique individuals. Generally, the more closely related a person is to another person, the more similar the person’s DNA is to that of the other person.
DNA is found in biological tissues and fluids, such as:
How Reliable Is DNA Evidence in a Criminal Investigation?
As any fan of true crime T.V. shows knows, DNA profiling has led to some amazing successes in criminal investigation. However, the reliability of DNA evidence in criminal cases depends on many factors. One of these is the quality of the DNA sample that law enforcement investigators are able to locate.
For example, law enforcement searched for the so-called “Green River Killer,” who had strangled at least fifty women in the vicinity of the Green River in Washington State for 20 years. The case was finally solved because of advances made in the analysis of DNA evidence.
However, DNA profiles are often not clean enough to permit the identification of a person with certainty. The best DNA sample is complete and allows examination of at least 16 different markers. These markers enable a person’s unique DNA identity to be shown.
Unfortunately, DNA can be damaged by exposure to moisture or extreme temperatures. If damaged, only some of the markers are available for analysis. Professional forensic analysts can generate only a partial profile. So, if a complete DNA profile allows a full picture of a person’s appearance, a partial profile might describe only one of their traits, e.g., eye color.
Who Uses DNA Criminal Evidence?
- Prosecutors: Over the past 20 years, prosecutors in criminal cases have been using DNA testing to prove that a suspect was at the scene of the crime and may even have been the perpetrator. This can be powerful evidence since a complete DNA sample can give nearly exact matches with relative certainty;
- Defense Attorneys: DNA testing can also be used by the defense to show that the suspect was not at the scene of a crime. The defense can use DNA analysis to prove the actual innocence of an alleged perpetrator. However, keep in mind that the fact that there is no DNA at a particular crime scene does not mean that an alleged perpetrator was not there. Other evidence may show this.
- Additionally, during trial, defendants may argue that test results are not accurate because of the corruption of the DNA sample, so only a few identifying segments of the DNA were obtained. Also, the competence of DNA testing can be disputed;
- The defense can argue that each segment represents a binary value, such that the odds of a match are much lower than the purported 1 in 100 billion. There are other ways to attack the credibility of DNA results as well;
- Innocence Projects. Organizations, such as the Innocence Project that are working to exonerate people who have been wrongfully convicted rely largely, although not exclusively, on DNA testing. This type of testing is crucial for their work, and they have succeeded in a number of the cases they pursue. DNA testing has exonerated 245 people, including around 18 who were on death row.
Where Is DNA Testing Available?
Currently, all states allow inmates claiming innocence access to DNA testing, although many of these statutes limit how far these tests can go.
Has DNA Evidence Helped to Exonerate a Person in a Criminal Case?
The first exoneration of a convicted felon took place in 1989. Again, according to the Innocence Project, there have been 375 more exonerations by DNA since that time. In addition, since 1989, tens of thousands of prime suspects have been subject to criminal profiling and pursued by law enforcement until testing of DNA samples showed that they were not the perpetrators of any crimes.
In 1995, the National Institute of Justice (NIJ) conducted a study of cases in the phase of investigation. It revealed that in more than 25% of the cases, suspects were excluded conclusively by DNA testing.
In one of the first cases of exoneration, on August 14, 1981, a man was accused of a rape in Norfolk, Virginia. The victim identified the man as the perpetrator. Her description matched that given by the victim of another perpetrator in another rape that had taken place on the same night.
The man identified as the perpetrator was convicted of 2 rapes and sentenced to spend 63 years in state prison. After serving 22 years in prison, the man was released when the prosecutor in Norfolk recognized that he had not committed either offense, as shown by analysis of DNA evidence.
In 1981, another Virginian was charged with raping, sodomizing, and robbing a woman in her home. The victim identified the man as her attacker, in spite of the fact that her own description did not match the man’s physical appearance. Nonetheless, the man was sentenced to life in prison in 1982.
Twenty years later, in June of 2002, Virginia courts passed a law that gave convicted felons the right to petition the courts for DNA testing. In 2003, the man was released when DNA testing showed that he could not have perpetrated the crime. The governor of Virginia at the time pardoned the man, and he was paid $1.5 million in compensation.
Another man was mistakenly convicted of rape, kidnapping, and felony assault in Cuyahoga County, Ohio in 1981. It was not until 2010 after he had spent more than 29 years in prison, that the criminal charges against him were vacated.
In 2004, a judge ordered DNA testing in the case, but because of a number of missteps by the prosecuting authority, it was not until 2010 that results from DNA testing proved the man’s complete innocence. The technology that allowed the samples to be tested individually had not been provided by the testing in 2008.
In 2002, prosecutors in St. Paul, Minnesota initiated a review of convictions in order to find out whether people had been wrongly convicted in their city. DNA analysis led to the discovery that a man had been wrongfully convicted of rape. It so happens that he was serving a life sentence for a double murder as well.
The attorney for Ramsey County had initiated a review of 116 convictions that had been obtained before 1995. The office wanted to see if new technology might change the outcome. Unfortunately, in 2 cases, the evidence needed for analysis had been destroyed. This has led to calls for law enforcement agencies to retain evidence as long as defendants are in prison or crimes remain unsolved.
In addition, again, it is important to note that there are thousands of cases in which DNA evidence led law enforcement to eliminate a suspect as a suspect and look further for the perpetrator. DNA evidence has led law enforcement to quickly focus on the right suspect and start to build a case against them.
Do I Need the Help of an Attorney for My DNA Issue?
If you have been charged with a crime or have been wrongfully convicted and you know there is untested DNA evidence available in your case, you want to consult a criminal defense lawyer immediately to ensure your rights are protected. LegalMatch.com can connect you to an accomplished criminal defense attorney who may help you identify flaws in a DNA test that may discredit untrustworthy results.
Other evidence may be faulty, e.g., eyewitness identifications and DNA analysis may be able to prove it. If you have been convicted, speaking with an attorney may help you gain access to post-conviction DNA testing.