Fifteen African American men who say they were framed by a corrupt Chicago police officer and his team, have had all the charges against them dropped.

Prosecutors said they were vacating all charges against the men, who were arrested by officers led by former police sergeant Ronald Watts. They said it was the first mass exoneration in the history of Cook County, which covers Chicago and the surrounding area.

The Exoneration Project, a free legal clinic at the University of Chicago Law School which represented the men, said all 15 were convicted of drug crimes from 2003-2008, and have all served their respective sentences.

In September, the men filed a lawsuit seeking to have their convictions overturned, claiming they had been framed by Watts, who was convicted in 2013 of stealing money from a drug courier who had been working as an FBI informant.

Among those whose conviction thrown out was Taurus Smith, who was 17 when he was first arrested and thrown in jail for a year. Speaking to The Independent from Chicago, Mr Smith said “it felt great” that his innocence had been recognised. He said he was trying to get his life back on track and find a job.

“I was in jail for a year. It was really scary. I was just a kid and you hear all these stories about what it’ll be like,” he said. Asked how he got through his time in custody, he said: “Family and friends and praying.”

The Chicago Police Department has long the target of accusations of abuse and mistreatment of suspects of colour. Earlier this year, the Department of Justice issued a scathing 164-page report that concluded the city’s officers were poorly trained and quick to turn to deadly and excessive force.

Lawyer Joshua Tepfer of the Exoneration Project, said it was the first time there had been a mass exoneration of suspects in the city. “It’s historic. It’s never happened before,” he said.

The clearing of the 15 men on Thursday marked the third day in succession that prosecutors at the Leighton Criminal Court Building in Chicago, dropped dropped charges because of alleged police misconduct.

On Wednesday Jose Maysonet, 49, walked free after 27 years behind bars for a conviction for a double murder prosecutors believed they could not longer rely on.

The Chicago Tribune said on Tuesday, 66-year-old Arthur Brown, was set free after serving 29 years for murder. Once again, prosecutors said they had “deep concerns” about the fairness of his conviction.

Wattts was jailed in 2013 after he and other officer, Kallatt Mohammed, were strongly criticised by the judge who heard their case.

US District Judge Sharon Johnson Coleman said the behaviour of Watts, who is himself African-American, was a betrayal of both his community and other officers. She said his actions were particularly shocking because he took advantage of a part of the community already struggling with poverty and crime.

Watts has since been released from jail.