City of Chicago attorneys claimed in a 2001 memo that prosecutors' decision to release one man from death row and charge another with murder was "political."
The Chicago Sun-Times reports that the memo was written after Anthony Porter sued the city for wrongful conviction.
Porter was released in 1998 after another man, Alstory Simon, made a videotaped confession claiming responsibility for a 1982 double murder.
Porter had served 16 years for the slayings. Cook County prosecutors charged Simon, who was convicted.
Prosecutors currently are re-examining Simon's conviction.
The memo doesn't say how attorneys concluded the decisions were political. But it says prosecutors decided the case "should be put to rest" partly because of negative publicity over the death penalty.
It also says there still was compelling evidence against Porter.