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DNA - A Great Tool With Limitations

Identification of an accused is often a crucial issue in criminal trials. The use of DNA evidence has proven very useful in confirming the identity of perpetrators of crimes and in exonerating the innocent.

DNA, however, does have its limitations. One major weakness may arise if the findings are inaccurate due to poor training or technique of the laboratory performing the DNA analysis. A second weakness may be the ability of the technician conducting the tests and a failure of the laboratory's quality control procedures. Finally, DNA results can be unreliable if law enforcement and crime lab personnel fail to properly collect samples and prevent contamination.

In order to ensure that DNA test results are accurate, the defense in a criminal case should have the benefit of consulting an independent and well-qualified DNA expert. Even when DNA test results are accurate and match the defendant, the result may fail to establish that the defendant committed the crime.

A recent problem was seen in the case of Miranda v. State, 38 Fla. L. Weekly D460a (Fla. February 27, 2013). The Second District Court of Appeals reversed a second-degree murder conviction because the state failed to prove the identity of the person committing the crime.

The state introduced detailed evidence of DNA from The Florida Department of Law Enforcement. There was a positive DNA match of blood obtained from the scene with the defendant. This evidence did not establish that the defendant committed the crime because there was no evidence as to when or how the defendant's blood was transferred to the items at the crime scene. The state also was not able to determine the age of the blood on the items at the crime scene.

This case highlights the importance of defense counsel confronting DNA testimony with the help of an expert.