DNA Testing in Criminal Prosecutions

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DNA Testing in Criminal Prosecutions

O.J. Simpson was acquitted of murder despite DNA evidence that identified him at the scene of the crime. Because of this, the public found questionable the jury’s verdict. However, just because a suspect’s DNA was found at the crime scene does not mean that the suspect committed the crime. 

Often, there are alternative explanations as to why one’s DNA was at a crime scene. In some instances, DNA can be illegally collected by law enforcement agents.

What Is DNA?

DNA, or Deoxyribonucleic Acid, is a molecule that serves as a blueprint that encodes the genetic framework of all living organisms. Since the 1980’s, FBI scientists have been at the forefront of DNA forensics for its use in criminal prosecutions. 

How Is DNA Used in Criminal Prosecutions?

DNA is used in criminal prosecutions to help identify the individual guilty of a crime. Every individual has a unique set of DNA, like a fingerprint, which can often be left behind a crime scene by a criminal through his or her blood, hair, semen, saliva, fingernails, or skin cells.

Thus, if DNA is left behind at a crime scene, scientists can compare the DNA with other individuals’ DNA to help determine someone’s potential involvement with a crime.

How Can Police Get Samples of a Suspect’s DNA?

Police can get samples of a suspect’s DNA if the suspect consents to providing a sample or if the police have other legal grounds to require that the suspect provide a sample.

Additionally, the FBI also maintains a national database of the DNA of convicted criminals through the Combined DNA Index System (CODIS) and the National DNA Index (NDIS). This system contains over 6,031,000 profiles of criminal offenders and other select individuals, but does not contain all DNA of the general public

Is DNA Testing Accurate?

After its introduction in the latter part of the 1980s, DNA test results slowly gained acceptance for use in criminal prosecutions. Expert witnesses have repeatedly confirmed the accuracy of DNA test results. Thus, they now are widely used and accepted in criminal courts alongside traditional forensic science such as the matching of blood type, hair, fingerprints, semen, and bite-marks.   

Can a DNA Match Be Wrong?

When scientists compare two sets of DNA, they compare a number of different points on each DNA sample to see if they match. If the scientists have two good DNA samples, they should be able to tell with near certainty whether or not the two samples match.

However, DNA samples may be incomplete or may degrade in which case the results of a DNA match may be less conclusive. In these instances, scientists may only be able to tell whether or not the DNA samples are a potential match or the results could be inconclusive all together.

Is Matching DNA Evidence Enough to Convict Someone of a Crime?

DNA evidence can be highly indicative of an individual’s involvement with a crime – especially if the DNA is found on an important piece of evidence like a murder weapon. However, in criminal cases, evidence must always overcome the "beyond a reasonable doubt" standard, which requires that a jury believe with a high degree of certainty that one is guilty of a crime given all of the evidence presented.

Seeking an Attorney’s Help

If you have criminal charges against you, it is important to contact an attorney right away to make sure you have professional representation in your criminal case. Hiring an accomplished criminal defense attorney can help identify any flaws with a DNA test that might discredit the results.

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Last Modified: 11-05-2013 03:15 PM PST

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