DNA is a key tool in Innocence Project's mission

For more than two decades, the Innocence Project has used DNA evidence to free the wrongfully convicted.

DNA is the "gold standard" for going back into old cases to prove where things went wrong, said Paul Cates, spokesman for the New York-based Innocence Project. "DNA exposes the cracks in the system in a way it hadn't been exposed before."

Since 1989, 330 people have been released from prison after DNA evidence showed they weren't connected to the crime. The Innocence Project has worked on 176 of those cases.

"To the best of our knowledge, those people are innocent," Cates said.

At a glance:

• The first DNA exoneration took place in 1989.

• Of 330 people who've been exonerated through DNA, 20 served time on death row. Another 16 were charged with capital crimes but not sentenced to death.

• Leading causes of wrongful convictions: eyewitness misidentification, invalidated or improper forensic science, false confessions and incriminating statements and informants who lie.

• More than 3,000 people write to the Innocence Project every year in search of help.

• The Innocence Project works on 250 to 300 cases at any given time.

• In about half the cases, DNA confirms the person's guilt.

• The length of time it's taken to win an exoneration has ranged from one year to 14 years.