Prisoners have no constitutional right to DNA testing to challenge their convictions, the Supreme Court ruled today in a 5 to 4 vote.

The majority seemed concerned that requests for testing would overwhelm—and possibly undermine—the courts. "The availability of new DNA testing, however, cannot mean that every criminal conviction, or even every conviction involving biological evidence, is suddenly in doubt," wrote Chief Justice John G. Roberts, Jr. in the majority opinion.

The power of DNA testing to overturn convictions is clear. DNA testing of biological traces—blood, hair, semen—has exonerated 238 people in the past 17 years, The New York Times reports.

The case before the court involved William Osborne, a convicted rapist in Alaska, who had sought post-conviction testing after deciding against a test in the original trial. Alaska law doesn’t make such testing available to at least some inmates, unlike the vast majority of states.

"There is no question that a small group of innocent people—and it is a small group—will languish in prison because they can't get access to the evidence," Peter Neufeld, a co-founder of the Innocence Project, told the Associated Press.

Although romanticized in popular crime shows, forensics has been criticized for flubbing procedures and overstating conclusions of murky analysis—from fingerprinting to fiber matching. A report released earlier this year by the National Academy of Sciences pinpointed nuclear DNA analysis the most objective, reliable tool for matching criminals to crime scenes.

Read more about how DNA testing is done.

Image courtesy of blmurch via Flickr