CHICAGO (AP) — A civil trial focused on the wrongful conviction of a former street-gang member who spent 18 years in prison for a double murder before being cleared is starting in Chicago.

Former death row inmate Nathson Fields was convicted in 1986 of killing two rival gang members. The one-time El Rukn member was released in 2003 and acquitted in a 2009 retrial.

The federal civil trial that begins Monday stems from a lawsuit brought by Fields alleging investigators fabricated or concealed evidence. It’s also a court-ordered do-over of a 2014 civil trial that concluded with an award to Fields of just $80,000.

Among the developments that seemed to taint legal procedures was the discovery of a case file in a police-station basement that plaintiff attorneys say could have cleared Fields earlier.