Since the early 1990s, DNA testing has exonerated 220 people in the United States who were convicted of crimes they didn't commit, according to the criminal justice reform group the Innocence Project. As the science of DNA testing improves, labs can go further and further back in time to test even damaged and partially decomposed DNA evidence. Partial tests, which can identify just a few genetic markers, aren't effective for establishing guilt, but they are useful in establishing innocence.
In jurisdictions where lawmakers and public officials are cooperating with innocence advocates and not blocking DNA testing, they're finding disturbingly high numbers of wrongful convictions. Dallas County, Texas, for example, has traditionally maintained strict evidence preservation guidelines, and voters there recently elected a district attorney who supports post-conviction DNA testing. The county leads the country with 17 exonerations since 2001.
Yet half the states still don't have laws requiring the preservation of DNA evidence in rape and murder cases, according to an August report in USA Today. Criminal defense lawyers continue to find old cases where there may be real questions about guilt, and where DNA testing could establish innocence, but where testing is impossible because prosecutors either destroyed or failed to properly preserve biological evidence.
While lawmakers profess concern about wrongful convictions and willingness to fund further DNA testing, such proposals often get attached to broader criminal justice bills with more objectionable provisions. In South Carolina, for example, Gov. Mark Sanford was set to sign a DNA preservation bill until the state legislature attached an amendment establishing a state DNA database that would include anyone arrested for (but not necessarily convicted of ) a crime.
Nor is legislation always implemented appropriately. In 2004 Congress passed the Justice for All Act, which appropriated $14 million to the Justice Department for distribution to the states to pay for DNA testing in possible cases of wrongful convictions. As of January, the Justice Department hadn't distributed a dime. In a press statement issued earlier this year, the law's sponsor, Sen. Patrick Leahy (D-Vt.), said federal officials had deliberately construed the bill's evidence preservation requirements as restrictively as possible, which allowed them to deny every grant request, even to states with good preservation standards.