DNA and the Innocence Revolution
Since the first DNA exoneration in 1989, biological evidence testing has freed more than 375 people in the United States who were wrongfully convicted — including more than 20 who had been sentenced to death. DNA testing didn't create wrongful convictions; it created the ability to prove they had always existed.
But DNA testing is not automatic, not always available, and not always sufficient. Understanding how it works in the post-conviction context — and what to do when it's possible — is essential for families trying to help a loved one who may have been wrongfully convicted.
When DNA Evidence Can Help
DNA evidence is most powerful in cases involving biological material from the crime scene that can be directly attributed to the perpetrator: blood, semen, saliva, hair with root attached, or skin cells. If that biological material exists, has been preserved, and was never tested — or was tested with older, less sensitive technology — post-conviction DNA testing may be possible.
DNA evidence is most commonly decisive in:
- Sexual assault cases where the perpetrator's DNA was deposited
- Murder cases where the perpetrator left blood, skin, or other biological material
- Cases where items from the crime scene (weapons, clothing, touch DNA surfaces) were collected but never tested
DNA is not helpful in cases with no biological evidence — where the conviction rested entirely on eyewitness testimony, confession, or non-biological forensic evidence.
How to Request Post-Conviction DNA Testing
Step 1: Find Out If Evidence Still Exists
Evidence preservation varies by jurisdiction. Some states have strong evidence preservation laws; others don't. The first step is determining whether the biological evidence from the original case still exists and where it's stored.
Request the evidence inventory from the case file. Contact the court clerk, the original defense attorney, or the prosecuting agency. Evidence is typically stored by the police department, the crime lab, or the court clerk's office.
Step 2: Know Your State's Post-Conviction Testing Law
Every state now has some form of post-conviction DNA testing statute, though they vary significantly in scope. Most require:
- That the evidence still exists and is in a condition allowing testing
- That the evidence was not previously tested, or that newer testing technology would produce more probative results
- That the results, if favorable, would raise a reasonable probability of a different outcome
Some states have narrow statutes that only apply to certain offense types. A post-conviction attorney or innocence organization can evaluate whether the state's statute applies to your loved one's case.
Step 3: File a Motion for Testing
A formal motion is filed in the trial court requesting access to the evidence for DNA testing. The prosecution typically has the opportunity to oppose the motion. Courts grant these motions when the statutory requirements are met — and increasingly, courts recognize that DNA testing is relatively cheap and that the interest in accurate verdicts weighs heavily in favor of testing when evidence exists.
Step 4: If Testing Excludes Your Loved One
A DNA result excluding the defendant from the biological evidence at the crime scene is powerful but not automatically dispositive. Courts still require that the result be connected to the actual perpetrator and that it undermines the basis of the conviction.
An exclusion result typically supports a motion for new trial or a habeas petition based on actual innocence. In many states, a DNA exclusion can also trigger review by a conviction integrity unit within the prosecutor's office.
What If DNA Testing Isn't Available?
Many wrongful conviction cases have no biological evidence. The wrongful conviction was based on eyewitness misidentification, a false confession, unreliable informant testimony, or flawed forensic evidence that isn't DNA-based. In these cases, other post-conviction avenues apply:
- Newly discovered evidence of other kinds (witness recantations, newly surfaced alibi evidence)
- Challenges to the non-DNA forensic evidence (which may have since been discredited)
- Ineffective assistance of counsel claims
- Brady violations (withheld evidence)
Organizations That Can Help With DNA Cases
- The Innocence Project (innocenceproject.org) — focuses specifically on DNA exoneration cases
- Innocence Network (innocencenetwork.org) — directory of regional innocence organizations that handle both DNA and non-DNA cases
- National Innocence Network member organizations — many have forensic science experts who can evaluate whether testing is viable