A man was freed Tuesday afternoon with the help of Northwestern Law School’s Center on Wrongful Convictions after serving 21 years of an 80-year prison sentence for a murder he did not commit.

Cook County prosecutors dropped charges against Jacques Rivera, 46, due to a witness recantation. The case’s only eyewitness was 12 years old when he identified Rivera as the shooter of a teenage boy, and said he later told police he had made a mistake, the Chicago Tribune reported. The judge ordered a retrial in September.

David Protess, co-founder of the Center and president of the Chicago Innocence Project, was not involved in the Rivera case and said he could not comment on specifics. However, Protess said the trial reflects the importance of witness recantations, noting three quarters of people freed based on DNA evidence in the United States were wrongfully convicted because of false witness testimony.

“This is a national phenomenon,” Protess said. “The reasons range from police pressure to falsely implicate someone to simply misidentifying the perpetrator.”

As a juvenile, Rivera case’s witness was probably more susceptible to this police pressure, he said. Protess said Rivera’s is the county’s 17th wrongful conviction overturned in the past 20 years after witnesses retracted their statements.

“No guilty people have been freed because witnesses change their story, which is why I think the policy of the state attorney’s office to threaten perjury charges against recanting witnesses is unwise,” Protess said. “Of course, I applaud my colleagues at the Center for a well-deserved victory.”

– Michele Corriston