Collection of DNA evidence may raise constitutional concerns

California readers of this criminal defense blog likely understand some of the importance attached to DNA evidence. The uniqueness of each person’s DNA is generally believed to make DNA evidence more reliable than fingerprints or other identification methods.

Yet not even DNA evidence is infallible. If improperly collected at a crime scene, DNA evidence can become contaminated, possibly leading to the wrongful conviction of an innocently accused individual. DNA evidence might also be subjected to degradation by environmental factors, such as heat, wetness, humidity, or other contaminants to which the sample may have been exposed along its chain of custody. In that regard, there have been several recent media stories of negligent DNA lab personnel who failed to keep DNA evidence free of contaminants.

Despite these potential concerns -- often raised by experienced criminal defense attorneys on behalf of their clients -- DNA continues to play an increasing role in criminal prosecutions and trials, for several reasons. The ease at which it can be collected -- from saliva, blood, skin tissue, bodily fluids or even hair -- also makes it a preferred evidentiary type among many law enforcement officials. Furthermore, only a very small sample amount is needed to collect and perform DNA analysis.

In felony cases resulting in a conviction, law enforcement may also collect DNA samples to add to an electronic database. With a simple mouse click, that database permits officials to crosscheck unidentified DNA samples collected at crime scenes against the DNA database of previous offenders. In fact, every American state currently collects DNA samples from felony convicts.

That database may soon be growing. The U.S. Supreme Court recently upheld a state’s practice of taking DNA swabs of individuals suspected of violent felonies or crimes at the time of their arrest, instead of waiting for the conviction. The practice is performed without a warrant.

Source:, “DNA Law in California May Not Be Protected By Recent SCOTUS Ruling,” Shawn M. Griffiths, June 4, 2013


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