CHICAGO (CBS) – For five days, one of the star witnesses in former Illinois House Speaker Michael Madigan's federal corruption trial has been on the stand testifying about his relationship to Madigan and his close associate and lobbyist Michael McClain.

Before the sun rose on a cold Wednesday morning in January 2019, Fidel Marquez agreed to a life-altering assignment as a cooperating witness in a criminal case the government was building against his colleagues at electric utility Commonwealth Edison and powerful Illinois House Speaker Michael Madigan.

Seizing on a tactic strengthened by a recent U.S. Supreme Court decision, defense attorneys in the Michael Madigan corruption trial began their cross-examination of a key witness Tuesday by trying to distinguish between exchanging jobs for official actions and simply currying favor with the formidable ex-House speaker.

Patrick Cotter, defense attorney for a longtime Madigan ally, spent more than three hours cross-examining former ComEd executive Fidel Marquez, trying to methodically rehabilitate his client.

A former ComEd executive -- turned government informant -- is back on the stand Wednesday for his fifth day in the corruption trial of former Illinois House Speaker Mike Madigan.

The former chief lobbyist for electric utility Commonwealth Edison has spent the last week telling a federal jury how he bent over backward to accommodate hiring requests from former Illinois House Speaker Michael Madigan.