Criminal defendants in California and around the country are often found guilty because of deoxyribonucleic acid analysis, but DNA can also be used to exonerate the wrongfully convicted. The accuracy of DNA testing became widely understood in the 1980s and 1990s when individuals who had spent decades behind bars began to be released. They were freed after tissue samples collected at crime scenes proved that other people committed the crimes they were incarcerated for. Newer techniques like cell-free fetal testing are even more reliable.
Incarcerated individuals who maintain their innocence can seek post-conviction DNA analysis if the technique was not available at the time of their trial or new and more accurate testing methods have been developed since. However, the U.S. Supreme Court ruled in 2009 that prisoners do not have a right to a post-conviction DNA test. Chief Justice John Roberts wrote in his opinion that granting such a right would undermine state laws.
That ruling may have actually prompted lawmakers to take action as the federal government and almost every state now has a law on the books that deal specifically with post-conviction DNA analysis. Such a law was signed in California by Governor Jerry Brown in September 2000. The California law requires the state to preserve DNA samples for at least as long as the defendant's prison term, ensures that petitions for post-conviction testing are considered even if the defendant pleaded guilty, and provides indigent defendants with legal assistance.
Experienced criminal defense attorneys might continue to work hard for the release of clients they believe were wrongly convicted. In addition to seeking post-conviction DNA testing, attorneys may look for what are known as Brady violations by scrutinizing trial transcripts and the information handed over during the discovery process. Prosecutors commit Brady violations when they fail to disclose exculpatory evidence or conceal information that could raise questions about the reliability of their witnesses.
Source: Findlaw, California Code, Penal Code - PEN § 1405