When people think of DNA and crimes, they usually think about the ways in which it can be used to convict criminals. However, in recent years, it has been used to actually do the opposite: to prove the innocence of previously charged people. Proving the innocence of people that have been charged for crimes is known as exoneration.
Why would people be charged for a crime they did not commit?
Occasionally there are crimes that are committed where there is very limited evidence surrounding the motive or the act. A person might have been charged for a crime based on a combination of factors including his or her proximity to the scene, his or her previous convictions and based on eye-witness accounts that were not reliable.
Where does DNA come in?
Since the 1990's when DNA became more reliable and effective in crime scenes, there have been projects working toward the exoneration of imprisoned people who have always claimed their innocence. DNA of the person who has been charged can be compared with the crime scene DNA, and there can be a scientific answer to whether the convicted person was present at the crime scene or not.
DNA and capital punishment
A high danger of capital punishment is the very real risk of punishing the wrong convict. It is widely believed that those on death row should be able to use any evidence that is available to them to prove their innocence. There are also many campaigners that are willing to fight for justice and use DNA evidence to reveal the truth behind crimes.
Source: Findlaw, "DNA as an exoneration tool," accessed Nov. 09, 2017