Frank Zampino, who was the No. 2 man in Montreal politics for several years, is due before the inquiry on Wednesday.
On Tuesday, close friend and former municipal fundraiser Bernard Trepanier completed his testimony, partly under publication ban.
Trepanier, who has been nicknamed ''Mr. Three Per Cent'' amid reports he took kickbacks, defended Zampino, saying the onetime right-hand man to former mayor Gerald Tremblay was never involved in the awarding of contracts.
Both Trepanier and Zampino are facing fraud charges in connection with a land deal in Montreal.
Zampino, the former head of the city's powerful executive committee, has been described by an engineering boss as being the man behind collusion at the city.
During a feisty cross-examination, Trepanier dismissed the notion that Zampino had been his real boss, adding that Tremblay was the man in charge of the Union Montreal party. Zampino left city hall in 2008.
Trepanier's defence of Zampino was so strong that he asked the lawyer representing the province's roadbuilders if he had a grudge against the former city official.
Trepanier continued to paint himself as a scapegoat for engineering bosses trying to pin the blame on him for collusion.
Witnesses at the inquiry have described how companies inflated the cost of public projects and divided up the extra cash among the Mafia, corrupt bureaucrats and Union Montreal, the party Trepanier raised money for.
Several engineering bosses have testified in recent weeks they were part of a corrupt system whereby they donated to the party in return for lucrative city contracts.
Trepanier was alleged to be a key figure in that scheme — the man who collected money on behalf of the party from the firms.
He was Union Montreal's chief fundraiser between 2004 and 2006, but continued to raise funds a few years after that.
The 74-year-old retiree maintains all he did for the party was sell tickets to fundraising events.
He has said he never collected any "cut" but the inquiry has shown he had a very close relationship with certain construction and engineering executives.
On Tuesday, the inquiry introduced a half-dozen pictures snapped at Trepanier's 70th birthday party.
Among those in the photographs were Michel Bissonnet, a former Quebec Liberal who took over as mayor of suburban St-Leonard from Zampino. Others included Zampino, other city officials and two engineering bosses Trepanier said were responsible for deciding which company got which contracts.
Trepanier has admitted he played a role in passing information to engineering firms and playing a role in dispersing contracts until the executives of two firms — Rosaire Sauriol of Dessau and Michel Lalonde of Genius — pushed him out because he knew nothing about engineering.
He insisted that at no time was Zampino involved. "I never talked about it with Mr. Zampino, never," said Trepanier.
Trepanier could not explain why so many witnesses have pointed the finger at him, but claimed again that all were stretching the truth about him and clandestine party funding.
In his testimony last month, Sauriol described Zampino as "the most powerful man in Montreal" and that he ran the city even though Tremblay was the mayor. Zampino left city hall in 2008.
Zampino made a brief appearance at the inquiry offices on Tuesday but did not appear because Trepanier was still testifying under a publication ban.
Trepanier has completed his time on the stand. Zampino will be up Wednesday.