Richard Roskuszka was the deputy chief. He says he was fired for complaining about misconduct by a tactical officer.
The city, mayor, former acting city manager and former police chief are all named in the lawsuit.
Roskuszka explained Wednesday why the thinks the alleged wrongdoing was allowed to go on.
"I personally believe he was afraid of being sued," he said. "And I brought that up during one of my meetings with the chief. He said his plate was full and he didn't want to deal with another lawsuit."
ABC7 has been unable to reach anyone from the city of Des Plaines for a response.