Former Chicago Alderman Daniel Solis has played a role in multiple federal prosecutions.
Solis' testimony is one of the most anticipated in the corruption case against Madigan.
The former alderman turned government mole eight years ago while still in City Council, recording many of his conversations with the then-speaker. In exchange for his help, Solis cut a deferred prosecution deal to avoid prison time for his own political misdeeds.
Solis took the stand Thursday for the first time as a government witness.
Evidence he collected led to Alderman Ed Burke's own corruption trial and conviction last year, but prosecutors at the time never called him to testify. Though, the defense did.
Solis' cooperation with the government began in mid-2016, when he was the chair of the powerful Zoning Committee in City Council. During his time as a government mole, Solis recorded his conversations with a variety of public officials, including Madigan.
Mike Madigan trial live updates: Former Ald. Michele Smith takes stand in ex-Illinois speaker trial
FBI Special Agent Ryan McDonald said on the stand Thursday afternoon investigators focused in on the speaker in 2017, after Solis recorded a meeting during which Madigan was heard asking Solis to introduce him to the developers of a high-rise apartment building in the West Loop called Union West.
Madigan said he would like to get their property tax business directed to his law firm, Madigan and Getzendanner.
Over the time of his cooperation, the FBI directed Solis to engage Madigan on various topics, including the possible re-development of a Chinatown parking lot and the redevelopment of the Old Post Office Building.
In each one, Solis was meant to lure Madigan in with the promise of getting business steered toward his law firm.
The indictment accuses Madigan of using his position as speaker to unlawfully steer business to his law firm, with his co-defendant, Mike McClain, carrying out illegal activity at Madigan's direction.
In turning government mole, Solis became only the second-ever sitting alderman to do so.
His testimony is expected to go well into next week, and could extend even further because of the upcoming holiday.
Former Cook County Commissioner Ed Moody testified Wednesday, saying under oath he held a no-work job for ComEd.
Court resumes Monday.
Madigan and Mike McClain face bribery and racketeering charges.
Related Coverage: How we got to here
Opening statements begin in former IL House Speaker Mike Madigan corruption trial
Jury selection begins this week in corruption trial of former Illinois House Speaker Mike Madigan
ComEd to pay $200M in federal bribery investigation; Illinois House Speaker Mike Madigan implicated in charge
House Speaker Michael Madigan polling Democratic caucus on whether he should step down
Special House committee to probe Michael Madigan bribery allegations stemming from ComEd investigation
IL House Speaker Michael Madigan continues to lose support amid ComEd investigation implications
Mike Madigan resigns as Democratic Party of Illinois chairman
Former IL House Speaker Mike Madigan indicted on charges including bribery, racketeering
Former IL House speaker Michael Madigan indicted on racketeering, bribery, more
Mike Madigan charged with crimes usually associated with Chicago mob
Michael Madigan indictment: Former House speaker pleads not guilty in federal corruption case
Former Illinois House Speaker Michael Madigan enters not guilty plea on all counts in federal case
All defendants found guilty on all counts in 'ComEd 4' trial surrounding ex-Speaker Mike Madigan
Jury finds Mike Madigan confidant Tim Mapes guilty in perjury case
Former Speaker Mike Madigan lawyers ask judge to dismiss 14 counts, citing recent SCOTUS ruling