Chicago – The drug convictions of 15 men have been thrown out after they claimed they were set up by a police sergeant, who went to prison for a related crime and his team of officers.

The convictions, in total 18, is believed to the first-ever mass exoneration in Cook County, the nation’s second most populous county.

“In these cases, we concluded, unfortunately, the police were not being truthful, and we couldn’t have confidence in the integrity of their reports and their testimony, and so, in good conscience, we could not see these convictions stand,” Mark Rotert of the Cook County Conviction Integrity Unit said in a news conference.

Seven other officers have been placed on desk duty pending an internal review of more incidents, the Chicago Police Department told CNN. Those officers all worked under Watts, CBS Chicago reported.

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Rotert, of the state’s attorney’s office, said his team is now reviewing additional cases connected to drug convictions spanning several years.

The men alleged that the police sergent Watts and his team of officers planted drugs on them during arrests between 2003 and 2008, falysiing reports, leading to their convictions, reports the Exoneration Project, a free legal clinic at the University of Chicago Law School that presented the cases to county prosecutors.

CNN reports, a Cook County judge on Thursday approved prosecutors’ decision to drop the charges. All the men had served their sentences for the crimes in question, according to the Exoneration Project: 14 are free, and one remains incarcerated on unrelated charges.

Read more at CNN