Florida police recently arrested a man for an alleged sex crime that occurred in 2007. Although it was a cold case, local authorities claim they resubmitted DNA evidence from the scene and were able to obtain a match with the man. Based on that new evidence, they were able to establish probable cause for the suspect and obtain an arrest warrant.
According to one non-profit research institute, every state now requires a DNA sample for sex offenders. Once collected, authorities use such DNA samples to search various databases, such as the FBI's Combined DNA Index System (CODIS). After entry into the CODIS system, DNA sample evidence remains active until there is a match found, even in cases that are decades old.
DNA evidence is perceived by many to make-or-break a criminal case. Yet a number of recent news stories have revealed that even this type of evidence is susceptible to error or tainting. Human error is an obvious culprit, and there have been instances where a lab technician failed to properly safeguard samples, resulting in their contamination and possibly leading to false identifications.
Yet even in the absence of lab contamination, there can be problems with the evidentiary samples that were taken from a crime scene. Collected samples may be of limited quantity, contain contaminants, or have degraded, all of which might produce incomplete or partial DNA profiles. Collected samples might also contain several different sources of DNA -- a mixture -- from which many different profiles could be identified as suspects.
At the same time, however, newly discovered DNA evidence has been useful in clearing suspicions for innocent suspects. Since 1989, the year of the first DNA exoneration, more than 2,000 people have been freed from prison after being wrongly convicted of serious crimes, according to the National Registry of Exonerations.
Criminal defense attorneys are needed by anyone accused of a sex crime, even when new DNA evidence appears to be strong, because the consequences of a rape conviction are very serious. Not all persons accused of sex offenses are guilty, and an experienced criminal defense attorney will locate all potential sources of evidence that could clear suspicion away from their client. An attorney will also examine the chain of custody of any DNA evidence, to ensure that it has not been tainted and that its results are reliable.
Source: NBC 6 Miami, "Man Arrested for 2007 Sexual Assault Based on DNA Evidence: Davie Police," Justin Finch, Aug. 31, 2012