While the inquiry will continue to conduct investigations and prepare for the fall session, the public testimony is done until after Labour Day.
A former Laval municipal official Friday was the last witness of a spring session that put a dent in Quebec's political and business class.
The inquiry has tackled everything from illegal political party financing, to engineering firms colluding on contracts, to organized crime's tentacles in the industry.
It has heard from 80 witnesses — engineering executives, city councillors, mayors, construction bosses, city officials and others.
Some witnesses described in detail so-called "turnkey" municipal election campaigns that made a mockery of Quebec's strict electoral laws. Engineering companies provided the money, manpower, and logistical support for a local campaign — and expected to cash in when their municipal candidate won.
Others described how municipal employees were routinely bought off to ensure that contract selection committees made favourable decisions.
At the provincial level, engineering firms pumped cash into political parties through middlemen, despite laws banning corporate donations. One former engineering exec explained that he did it to get the ear of politicians who controlled infrastructure grants.
Another suggested the practice also went on at the federal level, although the inquiry is not examining federal politics.
Meanwhile, the cost of projects skyrocketed through collusion and false-billing. While taxpayers got soaked, illicit profits were shared by companies, crooked bureaucrats, political parties, and elements of organized crime who threatened anyone hindering the collusive system.
Chief counsel Sonia LeBel said there was more to come.
"We have not completed our work," LeBel said. "On March 19th, knowing that our mandate was gigantic, the government gave us an extension to complete our work."
The inquiry requested and received an 18-month extension from the provincial government and must now submit its final report by spring 2015.
The probe heard from witnesses with memorable nicknames — such as "Mr. Three-Per-Cent," Union Montreal party fundraiser Bernard Trepanier, as well as retired construction boss Nicolo Milioto, who denied having claimed the nickname "Mr. Sidewalk."
Two of the most powerful politicians in the past decade in Montreal — three-term mayor Gerald Tremblay and his longtime former right-hand man Frank Zampino — also testified.
While many came to defend their reputation, others delivered explosive and self-damaging testimony.
Yves Cadotte, a former vice-president at SNC-Lavalin, admitted there was a cartel of engineering firms that divided work amongst themselves.
Cadotte testified the firms were routinely hit up for political donations and obliged, by reimbursing employees who made donations.
Rosaire Sauriol, a former vice-president at Dessau, a company his family founded, admitted to using false billing to funnel nearly $2 million to political parties.
Both men quit their posts after testifying. Sauriol, meanwhile, faces criminal charges — as do several other people who've testified.
The probe has destroyed careers, including that of ex-Montreal mayor Gerald Tremblay.
He recently testified, and vehemently denied the claims of a previous witness who said Tremblay turned a blind eye to illegal fundraising.
In fact, he said he even tried once to report an extortion attempt from "Mr. Three-Per-Cent" to the ex-local police chief, and the chief didn't interfere. The former chief denies Tremblay's account.
Tremblay's interim successor, Michael Applebaum, who has not been called to testify, was slapped this week with fraud charges and quit.
"We are aware of the importance of our work and the confidence that people have in us," LeBel said.
"We are also aware of the impact that our work has on the lives of many, but it is in the public interest — in the interest of all — that we can accomplish the mandate given to us without detours and in an efficient manner."
LeBel said the coming weeks will be used to prepare for September.
Chair France Charbonneau must deliver her report by April 2015. The inquiry will be required to submit a progress report by Jan. 31, 2014.
Charbonneau thanked everyone involved, before adjourning for the summer.
"We wish you a warm summer with lots of sun and we'll see you on Sept. 3rd," Charbonneau said.