CHICAGO -- The Cook County state’s attorney is investigating whether a former Chicago police sergeant tainted far more convictions than those he has been held accountable for.

State’s attorney spokeswoman Tandra Simonton said the office’s Conviction Integrity Unit is reviewing any cases of incarcerated individuals where former Sgt. Ronald Watts was substantively involved.

Watts was convicted in 2013 and sentenced to 22 months in prison for extorting protection payoffs from drug dealers. An officer on his team, Kallatt Mohammed, was also convicted and given prison time. Four drug convictions involving three defendants have been tossed be because of the officer’s wrongdoing, reports the Chicago Tribune.

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Joshua Tepfer of the University of Chicago’s Exoneration Project says prosecutors are working with Exoneration Project lawyers and will be appointing a special master to review the cases. Prosecutors agreed to examine potentially hundreds of convictions involving Watts and officers he supervised, according to the paper.

Tepfer says the Exoneration Project on Monday withdrew their petition for a court review of convictions in cases handled by Watts and his team.