The identification of suspects in criminal cases has undergone two revolutionary developments since the late 19th Century. The first was the development of fingerprinting methods for police work in the 1880s, and more recently the introduction of DNA profiling, also known as DNA fingerprinting. If you watch crime dramas or documentary programs on television, you will commonly see either or both of fingerprinting and DNA profiling methods being used by police and prosecutors; it can seem that DNA evidence is a veritable “magic bullet” when it comes to solving cases that might otherwise never be resolved.

How do law enforcement agencies use DNA sampling?

DNA profiling serves two main purposes for police investigators. The most common use is to use a DNA sample of a “person of interest” to eliminate that individual as a criminal suspect; the other purpose is to add scientific forensic evidence to support the prosecution’s claim that the accused is in fact perpetrator of the crime. Key to either of these uses of DNA evidence is the collection of DNA samples in a central database, the most well-known of which is the Federal Bureau of Investigation’s Combined DNA Index System, or “CODIS” for short. This database works by comparing two sets of DNA samples, one consisting of samples taken from convicted criminals and the other samples collected from crime scenes or victims of crimes and submitted for comparison. If a match exists between the two sets, this can provide investigators with a strong lead to a suspect.

Is DNA profiling always reliable?

Like any other technology used in law enforcement, DNA testing has evolved from its infancy into a much more sophisticated and reliable methodology in use today. This does not, however, mean that DNA evidence is beyond question or that it cannot lead to mistaken outcomes in criminal trials. Some of the potential problems that exist in connection with the use of DNA samples include:

  • Incomplete DNA profiles. Not every DNA sample is perfect; sometimes a sample can become so degraded that it can lead to what is called a “coincidental” match with someone other than the person from whom the sample was taken.
  • Mixed DNA samples. Sometimes a DNA sample can include genetic material from two or more individuals. This can make it difficult to determine from whom the sample was actually taken, particularly when the database against which the sample is compared is extraordinarily large, such as CODIS; that in turn can lead to an incorrect coincidental match.
  • Sample cross-contamination. This can result from an inadvertent transfer from one sample to another in the laboratory, or from something as simple as sample mislabeling.
  • Laboratory errors. These can result from “clerical” mistakes such as assigning an incorrect profile to a DNA sample, such as through a typing error.

New Oklahoma bill may make it easier to get your DNA

Despite its potential problems, the use of DNA evidence in criminal cases has become increasingly common and the faith that prosecutors put in it shows no signs of abating. Indeed, proposed legislation has recently passed the Oklahoma House of Representatives that would make it easier for police to collect DNA samples from individuals even before they are convicted of a crime. If it becomes law the bill would allow police in felony cases to take DNA samples and hold them outside of the state’s DNA database until such time as the prosecution decides to take the case to trial.

Although the proposed legislation still has yet to clear the state Senate, its supporters note that this particular attempt at expanding DNA sample collection has made it further through the legislature than any of its predecessors. It remains to be seen how the battle between advocates of privacy rights and proponents of the bill – who claim that it would assist in securing more convictions while protecting the innocent – will turn out in the Senate.

Regardless of whether the proposed legislation becomes law or not, an experienced criminal defense attorney must be aware of how to challenge the use of DNA evidence not only on technical grounds like those identified above but also for its potential to confuse and even mislead jurors into making erroneous convictions.

If you or a loved one has been charged with a crime, contact the Hunsucker Legal Group at 405-231-5600 for a free consultation.