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DNA evidence is used in less than one percent of criminal cases. But it’s used in the most serious cases and can be the deciding factor.
The experienced Columbia criminal defense lawyers at Shealey Law Firm explain DNA in criminal investigations and what you need to know.
What Is DNA Evidence and How Is It Collected?
DNA evidence is biological genetic testing offered in court to prove or disprove facts relevant to a legal proceeding. The cells of living organisms, including humans, contain genetic information. This information tells the cell how to grow and function. Except for identical twins, each person has unique DNA.
Types
Common bodily substances where DNA is found at a crime scene include:
- Blood
- Saliva
- Semen
- Skin
- Hair
- Bone
- Sweat
DNA evidence is not discernible by sight. It must be scientifically tested, and a qualified person must present the results as evidence.
How DNA Testing Is Used in Criminal Cases
In criminal cases, DNA identifies or excludes suspects. Because each person’s DNA is unique, markers can be distinguished among individuals.
While DNA can be used to identify or exclude suspects, a positive DNA match does not automatically mean a person committed a crime or necessarily makes someone guilty of a crime.
Real-Life Examples of DNA Clearing the Wrongfully Accused
The Innocence Project reports that DNA evidence has exonerated prime suspects in more than 10,000 cases. Many of these suspects were cleared before their cases were charged or before trial.
Perry Mitchell
Perry Mitchell was the first DNA exoneree in South Carolina in 1998. He spent 15 years in prison, convicted of rape. The victim identified Mitchell in a photo lineup. Years later, when a court ordered DNA testing, it wasn’t a match.
Leonard Mack
Leonard Mack spent 47 years in prison, wrongfully convicted of rape and weapons charges. The conviction was largely the result of unreliable witness testimony.
Gary Dotson
In 1989, Gary Dotson was the first person in the United States exonerated through DNA testing. Although convicted of rape, no rape had occurred. The victim fabricated the allegations, including identifying Dotson from a photograph and a lineup. There was also incorrect forensic testimony against Dotson. Convicted at 22 years old, Dotson spent 10 years in prison trying to clear his name.
Limitations and Controversies Surrounding DNA Evidence
Despite the seeming reliability of DNA evidence, it has limitations. Some of the problems with DNA evidence include the following:
- Samples must be preserved correctly.
- The crime scene must be free of contamination.
- An accurate record of those with crime scene access must be kept.
- Chain of custody must be kept.
- Testing must be done correctly.
- Results must be interpreted accurately.
- Not all crime scenes have DNA evidence.
- There may be an innocent explanation for the presence of DNA.
- Other information, such as prior consensual partners in a sexual assault case, may be needed.
- A DNA profile may be incomplete.
DNA profiles for people convicted and even accused of certain offenses are routinely taken in the United States. But they’re not always uploaded into CODIS (the Combined DNA Index System), which allows law enforcement agencies to share profiles. Missing information can prevent identification of suspects.
DNA Evidence in Criminal Defense
Discovery
A criminal defendant may demand discovery of DNA evidence. Rule 5 of South Carolina criminal procedure allows inspection and copying of scientific test results, if known by the prosecution and intended to be used against the accused. The defense also has a duty to disclose scientific testing they intend to use.
Exculpatory evidence
In addition, the prosecution must disclose exculpatory evidence (Brady v. Maryland). If DNA testing may disprove the guilt of the accused, the prosecution must tell the defense.
Testing
A strong criminal defense involving DNA evidence should investigate testing procedures and results. The defense may request to watch DNA testing, either in person or virtually.
The court may not always allow it for practical reasons. In addition, you may ask for the DNA to be sent to an independent lab for additional testing. Court motions should be made early in the criminal defense process.
Testifying
To testify about DNA testing, a person must be qualified as an expert. The defense shouldn’t just accept the state’s agent as an expert, nor that the results were done properly. Challenging state witness qualifications and testing procedures can be a viable defense path.
Appeal
South Carolina allows a convicted person to apply for DNA testing. A person who pleads not guilty, who is subsequently convicted, and who proclaims innocence may petition the court. If results are exculpatory, it may be grounds for a new trial (§ 17-28-30).
The Future of DNA in South Carolina Criminal Investigations
- From 1989-2020, 375 people in the United States were exonerated of criminal convictions because of DNA. Twenty-one of them were on death row.
- Forty-four falsely pleaded guilty to charges.
- Twenty-nine percent made false confessions.
- Sixty-six percent of exonerations involved convictions based on eyewitness misidentification.
- One hundred thirty had been wrongfully convicted of murder.
DNA can be used both to identify and exclude suspects. However, DNA is not always available, reliable, or conclusive.
Contact a Columbia Criminal Defense Lawyer
If you are suspected of or charged with a crime, contact an experienced attorney at Shealey Law Firm today.